ALBERT

Description: Aims Accumulation of p-hydroxybenzonic acid (PHBA) in soil will cause plant stress. Our aims were to characterize PHBA-degrading Pseudomonas putida CSY-P1 and to assess its role on alleviating PHBA stress in plants. Methods Strain CSY-P1 was isolated from rhizosphere soil, and its properties were investigated. The effects of CSY-P1 on soil enzymes and oxidative damage in plants were analyzed. Under PHBA-contaminated environments, antioxidant enzyme activities in CSY-P1 were assessed. Results Optimal conditions for degradation of PHBA by CSY-P1 were 28 °C, pH 9, and an initial PHBA concentration of 0.6 g l −1 . Protocatechoic acid was a metabolite. CSY-P1 decomposed PHBA effectively in unplanted autoclaved soil. After the strain was applied to PHBA-contaminated cucumber-planted soil, activities of some soil enzymes were increased and the PHBA concentration in soil decreased. Some antioxidant enzyme activities in leaves were elevated, thus reducing malondialdehyde levels in seedlings and mitigating PHBA stress in cucumber. Catalase activity in PHBA-exposed CSY-P1 increased. Conclusions Pseudomonas putida CSY-P1 degrades PHBA in autoclaved soil and alleviates PHBA stress to plants by inducing some soil enzymes and antioxidant enzymes in leaves. Catalase in strain CSY-P1 contributes to its PHBA tolerance, making it a promising strain for remediation of PHBA-contaminated soil.

Description: Background and Aims Given that plant growth is often water limited in drylands, it has been proposed that water seems to influence productivity by altering physiological/metabolic responses and nutrient availability in short term. It is unclear, however, whether water mediates a positive plant-soil feedback and whether the feedback drives variations in plant productivity. Methods A 4-year field experiment was performed to examine the effects of water and nitrogen (N) addition on nutrient concentrations in soil and plant, nutrient resorption and potential return, in a temperate grassland in northern China. Results Water addition enhanced plant N and phosphorus (P) concentrations but reduced plant N and P resorption efficiency, leading to the increased potential N and P return to soil via litterfall. Enhanced nutrient potential return likely contributed to an increase of plant productivity in the following year. These “fertilization effects” caused by water addition were similar to those by N addition. Conclusions Our study suggests that the positive plant-soil feedback induced by increased precipitation may have a role in water-induced increases in productivity, and highlights the “fertilization effect” of water addition in a semiarid grassland in short term.

Description: Aims In deserts, moss-dominated crusts may play an important role in terrestrial-aquatic and aboveground-belowground connections. Despite its importance, very little is known about moss’s role in biogeochemical cycles and how nutrient pulses (e.g., from N deposition in air pollution) will affect their functional significance as an integrator of nutrient cycling in deserts. Methods Moss and soil were sampled from 15 sites in the Sonoran Desert in and around Phoenix, covering the city core subject to N deposition and rural areas to the east and west. Samples were analyzed for C, N, P and micronutrient content to compare moss stoichiometry over a gradient of soil resource availability. Results Moss %N and %P were positively correlated with soil N and P. Thus, sites in the city core subject to N deposition tended to have higher soil N and therefore higher moss N than the sites outside the city core. Micronutrient content varied with sampling region but was not related to soil content. Conclusions Results suggest that moss can take up excess N,, but overall coverage of moss is lower in the city, limiting its ability to act as a N sink.

Description: Background and Aims Fire has profound effects on ecosystem properties, but few studies have addressed the effect of repeated burns on soil nutrients, and none have been conducted in cold desert ecosystems where invasion by exotic annual grasses is resulting in greater fire frequency. Methods In a 5 year study, we examined effects of repeated burning, litter removal, and post-fire seeding on carbon (C) and nitrogen (N) contents in soils, litter, and vegetation in a cheatgrass-dominated Wyoming big sagebrush ecological type. We developed a multivariate model to identify potential mechanisms influencing treatment effects and examine the influence of environmental factors such as precipitation and temperature. Results We found that repeated burning had strong negative effects on litter C and N contents, but did not reduce soil nutrients or vegetation C and N contents, likely due to cool fire temperatures. There were few effects of litter removal or post-fire seeding. Instead, precipitation and temperature interacted with burning and had the strongest influences on soil N and vegetation C and N contents over time. Conclusions Management strategies aimed at decreasing litter and seed banks and increasing competitive interactions may be more effective at reducing cheatgrass success than approaches for reducing soil nutrients.

Description: Background In this issue, Schenkeveld and coworkers described the potential of phytosiderophores (a class of root exudates) to mobilize metals in the rhizosphere by an equilibrium modelling approach. Scope The rhizosphere is a complex and dynamic environment where several different organic and inorganic compounds coexist. Due to the different concentration and chemical characteristics there might be competitive and synergistic interactions. However the rhizosphere is strongly influenced by root activity: water and nutrient uptake, root respiration that might modify the pH and redox status of the rhizosphere. Thus, how does the complexity of the system and the dynamics influence the thermodynamics of the single process? Can chemical equilibria be really reached in the rhizosphere? Issues related to kinetics vs thermodynamics are discussed. The study of the single processes is important but more complex researches, being thus more realistic (i.e. field-like conditions), are necessary. Hence, what are the available tools/methods in rhizosphere research? What are the drawbacks? How can the results of these methods be related to thermodynamic and kinetic models? Conclusions Besides stimulating further awareness around the rhizosphere complexity, tentative answers are given highlighting the future challenges in rhizosphere research, essential knowledge for the development of agronomic practices ensuring a better exploitation of soil endogenous resources of nutrients by crops.

Description: Background Nitrogen (N) and phosphorus (P) availabilities affect plant growth and the balance of elements, yet how these plant traits respond to N and P supply remains unclear. Methods We explored the effects of N and P supply on the growth rate, leaf N and P concentration, and nutrient resorption of Arabidopsis thaliana in a greenhouse fertilization experiment. Results Relative growth rate increased with mature green-leaf N:P ratio (N:P gr ) when N-limited, but decreased with N:P gr when P-limited, suggesting that the growth rate hypothesis might be related to the type of nutrient limitation. In N-limited A. thaliana, addition of P did not significantly affect the leaf N concentration. However, in P-limited A. thaliana , addition of N decreased the leaf P concentration. Addition of N increased P resorption efficiency, and addition of P stimulated N resorption efficiency. Consistent with the predictions of the relative resorption hypothesis, the difference in the proportionate resorption of N vs. P declined with increasing N:P gr . Conclusions Our results suggest that N and P jointly regulate growth rate, leaf stoichiometry, and nutrient resorption of A. thaliana , and highlight that the interacting effects of nutrients should be considered when predicting future responses of plant functional traits to global change.

Description: Background and aims In a previous study, a compost water extract (CWE) applied to pea seedlings resulted in 〉95 % protection against root infection. The protection was correlated with retention of a sheath of root border cells surrounding each root tip. A transient exposure to CWE was correlated with 80 % reduction in infection, and with retention of border cell sheaths. Early effects of CWE on border cell dispersal therefore were examined. Materials and methods Temporal and spatial dynamics of pea, maize, cotton, and cucumber border cell dispersal into water or CWE were measured. Results Border cells formed a mass surrounding root tips within seconds after exposure to water, and most cells dispersed into suspension spontaneously. In CWE, 〉90 % of the border cell population instead remained appressed to the root surface, even after vigorous agitation. In cotton, for example, 〉25,000 border cells dispersed within seconds of immersion in water, but 〈100 border cells dispersed after 〉24 h in CWE. Conclusions Border cells can contribute 〉90 % of carbon released from young roots, and a single border cell can trap hundreds of bacteria within minutes. The impact of altered border cell dispersal on soil properties, plant nutrition, and root disease development warrants further study.

Description: Background and aims The objectives of this study were to elucidate the mechanisms of interaction between root exudates of tall fescue and functional bacteria associated with petroleum degradation and whether components of the exudates can enhance petroleum removal from soil. Methods Root exudates of tall fescue were collected through a continuous root exudate trapping system and identified by GC-MS. Chemotaxis, swarming, and in vitro assay were conducted to assess the effects of the organic acids of root exudates on Klebsiella sp. D5A (plant growth promoting rhizobacterium), Pseudomonas sp. SB (biosurfactant producing bacterium), and Streptomyces sp. KT (petroleum-degrading bacterium). A pot experiment with organic acid amendment was conducted to study the effects of these components of root exudates on petroleum remediation. Microbial physiological metabolisms affected by organic acids were tested using Biolog Eco plates. Results Palmitic acid was found to be most effective in promoting D5A colonization on tall fescue. ρ-Hydroxybenzoic and palmitic acids significantly stimulated the growth of strains D5A, SB, and KT. Furthermore, palmitic acid amendment significantly enhanced petroleum removal in pot experiment. Conclusions Palmitic acid was the critical organic acid to facilitate petroleum removal during phytoremediation. These findings provide insight into the mechanisms by which tall fescue enhances the degradation of petroleum.

Description: Aims Leaf and root phenology play important roles controlling plant productivity and ecosystem function, yet, few studies link patterns of leaf and root phenology across woody species. Trees with diffuse-porous wood anatomy tend to leaf-out before ring-porous species and we expected that increases in transpiration with spring leaf-out would be coupled with initiation of root production to support uptake of soil resources. Therefore, we hypothesized that the timing of root production would follow patterns of leaf production and wood anatomy. Methods Root production was observed using minirhizotrons and related to leaf phenology across six temperate tree species with different wood anatomy in a common garden. Results As expected, leaves of diffuse-porous species emerged before ring-porous, followed by tracheid species. Root production peaked before bud break in five of the six species and before maximum leaf area index in all species, but did not follow expected patterns with leaf production. Conclusions Our observations did not indicate tight linkages between root and leaf phenology but do highlight the potential for very early season root production and greater variation in the phenology of roots than leaves. Future work should identify the environmental factors and species traits that best explain variation in root phenology.

Description: Background and aims As plants approach maturity and start to senesce, the primary sink for phosphorus (P) is the seed but it is unclear how plant P status affects the resulting P concentration and speciation in the seed and remaining plant parts of the residues. This study was established to measure how P speciation in different parts of wheat and canola is affected by plant P status. Methods Wheat and canola grown in the glasshouse were supplied three different P rates (5, 30 and 60 kg P ha −1 equivalent). At physiological maturity, plants were harvested and P speciation was determined for all plant parts (root, stem, leaf, chaff/pod and seed) and rates of P application, using solution 31 P nuclear magnetic resonance (NMR) spectroscopy. Results Phytate was the dominant form of P in seed whereas orthophosphate was the dominant form of P in other plant parts. The distribution of P species varied with P status for canola but not for wheat. The phytate content of wheat chaff increased from 10 to 45 % of total P as the P rate increased. Canola pods did not show a similar trend, with most P present as orthophosphate. Conclusions Although minor differences were observed in P speciation across the three P application rates and plant parts, the effect of this on P cycling from residues into soil is likely to be relatively minor in comparison to the overall contribution of these residues to soil P pools. This glasshouse experiment shows the dominant P form in crop residues that is returned to soil after harvest is orthophosphate, regardless of plant P status.

Description: Background and aims Variations in microclimate and soil characteristics on mountain slopes influence forest structure and function. Precipitation, incoming solar radiation and relative humidity change along a mountain slope. Equally, soil depth and the amount of stored soil moisture vary. The objective of this study was to examine the impacts of these factors on forest water use in mountainous terrains. Methods Transpiration of four temperate deciduous forest stands located at different elevations in South Korea was monitored with a sap flow technique throughout the growing season in 2010. The study sites were located on the north slope at 450 m (450 N), 650 m (650 N), and 950 m (950 N). To examine the effect of aspect, an additional site with a southern aspect was studied at 650 m (650S). All the sites were dominated by Quercus species, with leaf area index ( L ) ranging between 5 − 6 m 2  m −2 . Results Rainfall increased, while air temperature ( T A ) and daytime vapor pressure deficit ( D ) decreased with increasing elevation. We did not observe any gradients in solar radiation ( R S ), soil moisture and sap flux density of the individual trees ( J st ) with an elevational gradient. Sapwood area ( A S ), i.e., hydro-active xylem area, and daily maximum tree water use (max TWU) increased non-linearly with increasing diameter at breast height (DBH). Neither A S nor max TWU varied among tree species or along the elevation. The total annual canopy transpiration ( E C ) was 175, 115, 110, and 90 mm for 450 N, 650 N, 650S, and 950 N, respectively. E C declined with increasing elevation as a result of decreasing length of the growing season, D , and T A along the elevation. Significantly ( P 〈 0.001) higher stomatal sensitivity to changes in D was found at the 950 N, leading to lower annual E C and lower water use efficiency (WUE) at this elevation. Conclusions We conclude that differences in E C exist along the mountain slope studied, corresponding to changing T A , D , length of the growing season, and stomatal sensitivity to D , which should be considered when establishing forest catchment water balances.

Description: Background and aims Wetlands are important carbon sinks across the planet. However, soil carbon sequestration in tropical freshwater wetlands has been studied less than its counterpart in temperate wetlands. We compared carbon stocks and carbon sequestration in freshwater wetlands with various geomorphic features (estuarine, perilacustrine and depressional) and various plant communities (marshes and swamps) on the tropical coastal plain of the Gulf of Mexico in the state of Veracruz, Mexico. These swamps are dominated by Ficus insipida, Pachira aquatic and Annona glabra and the marshes by Typha domingensis, Thalia geniculata, Cyperus giganteus, and Pontederia sagittata . Methods The soil carbon concentration and bulk density were measured every 2 cm along 80 cm soil profiles in five swamps and five marshes. Short-term sediment accretion rates were measured during a year using horizontal makers in three of the five swamps and marshes, the carbon sequestration was calculated using the accretion rates, and the bulk density and the percentage of organic carbon in the surficial layer was measured. Results The average carbon concentration ranged from 50 to 150 gC kg −1 in the marshes and 50 to 225 gC kg −1 in the swamps. When the wetlands were grouped according to their geomorphic features, no significant differences in the carbon stock ( P =  0.095) were found (estuarine (25.50 ± 2.26 kgC m −2 ), perilacustrine (28.33 ± 2.74 kgC m −2 ) and depressional wetlands (34.93 ± 4.56 kgC m −2 )). However, the carbon stock was significantly higher ( P  = 0.030) in the swamps (34.96 ± 1.3 kgC m −2 ) than in the marshes (25.85 ± 1.19 kgC m −2 ). The average sediment accretion rates were 1.55 ± 0.09 cm yr −1 in the swamps and 0.84 ± 0.02 cm yr −1 in the marshes with significant differences ( P  = 0.040). The rate of carbon sequestration was higher ( P  = 0.001) in swamp soils (0.92 ± 0.12 kgC m −2  yr −1 ) than marsh soils (0.31 ± 0.08 kgC m −2  yr −1 ). Differences in the rates of carbon sequestration associated with geomorphic features were found between the swamp ecosystems ( P  〈 0.05); i.e., higher values were found in the swamps than in the marshes in perilacustrine and estuarine wetlands ( P  〈 0.05). However, no significant differences ( P  = 0.324) in carbon sequestration rates were found between the marsh and swamp areas of the depressional site. Conclusions Swamp soils are more important contributors to the carbon stock and sequestration than are marsh soils, resulting in a reduction in global warming, which suggests that the plant community is an important factor that needs to be considered in global carbon budgets and projects of restoration and conservation of wetlands.

Description: Background and aims Our objective was to relate chemical composition of roots of a wide range of annual crops to root decomposition, so as to assess roots potential contribution to soil carbon (C). Methods Roots from 20 different crops and 4 botanical families, collected under field conditions were incubated in soil for 120 days at 25 °C. The initial chemical composition of roots was determined. The C mineralization was assessed by the continuous measurement of CO 2 release and using single exponential model. PCA analysis was used to explore qualitative pattern in root quality and decomposition. Results PCA analysis showed that chemical characteristics (traits) differentiated plant families. The mineralization of root C varied greatly in terms of kinetics and in the total amount of C mineralized (36 % to 59 % of added C). Mineralization constant ( k value) was negatively correlated with hemicelluloses and positively with N content. Poaceae roots that combined high hemicelluloses, low cellulose and low total N, showed low degradation rate and cumulative C mineralization. Conclusions The chemical composition of roots, as for the above-ground parts of plants, can correctly predict their rate of decomposition in soils. The taxonomic affiliation enhances the understanding of the chemical determinants of quality of roots.

Description: Aims Despite many studies on the impact of arable land conversion to Short Rotation Coppice (SRC), few studies have been carried out on soil biota. This study aims at assessing biological and physico-chemical soil properties that are affected by SRC compared to forestry, grassland and an agrosystem. Methods All samples were collected in the Aisne valley (France), from the same type of soil, with four land uses, i.e. willow SRC, agrosystem, grassland and alluvial forest, 3 years after SRC was planted. We studied fertility, the biological community (earthworm diversity, density and biomass, bacterial and fungal density and community structures) and biochemical parameters (enzyme activities, basal respiration and nitrification). Results After 3 years’ growth, soil biological parameters (fungal abundance, laccase activity, anecic earthworm proportion and earthworm diversity) and CEC were higher in the SRC than in the agrosystem soil. In parallel, fungal abundance was higher in SRC than in forest and grassland soils. Conclusion Compared to annual arable crops, SRC promoted biological properties. However, in the short term, the parameters we measured were lower than in the forest and grassland soils. The use of certain parameters as indicators of soil functioning/quality assessment to discriminate the four land uses is discussed.

Description: Aims Root and shoot biomasses and their ratio (R:S) were determined for three stages of forest regeneration (18, 40 and 〉 60 years.), and for open and dense vegetation, in four soil classes in the semi-arid region of Northeast Brazil. Methods Shoot biomasses were estimated by allometry and roots were collected in 0.7 × 0.7 × 1 m trenches. Results Root and shoot biomasses and the R:S ratio were over double in the 〉60 year-old vegetation (R:S = 0.67) when compared to more recent regenerated areas (0.32). In dense vegetation the biomass of roots and shoots were also more than the double of those in open vegetation but the R:S ratios were not significantly different (0.51 and 0.49). Litholic Neosols had lower ratio (0.22) than the other soil classes (0.53 to 0.63) and dense and open vegetation did not differ. In all areas except in deep sandy Quartzarenic Neosols most of the roots (〉 90 %) were in the upper 40-cm layer of the soil profile, and consisted of coarse roots. Conclusion Root biomass accumulates more slowly than aboveground biomass and it takes several decades to stabilize in shallower soils. The R:S ratios are higher when compared to other dry land forests, probably due to low water availability.

Description: Objectives To identify parameters that can be used for the analysis of natural variation in leaf senescence of wheat; and to understand the association between the onset and progression of leaf senescence with N uptake and root traits. Methods Chlorophyll content and the proportion of yellow leaves were used as senescence indicators and their relation with other morphological and physiological traits were measured in contrasting early senescing (ES) and late senescing (LS) wheat lines. Results There were significant genotype effects on the onset and progress of senescence. The ES lines in which leaf senescence commenced early had significantly lower root biomass and N uptake than LS lines. The strong negative association between the extent of leaf senescence with root biomass and N uptake indicated that the poor root growth induced N limitation caused the early senescence of ES lines. Conclusions The leaf senescence development in ES lines was precocious and constitutive as the trait expressed even under optimal growth conditions suggesting they could be useful in understanding the genetic regulation of senescence under different abiotic stress situations. Accelerated leaf senescence in wheat could be a mechanism to compensate for limitations in the root system that tend to restrict nutrient uptake.

Description: Background The promoted root growth under developmental plasticity triggered specifically by mild drought stress (MDS) is known to contribute to maintained water uptake and dry matter production (DMP). Aims To examine whether the expression of developmental plasticity of root systems and its contribution to DMP would be affected by the levels of nitrogen (N) application. Methods Two genotypes (CSSL50 derived from Nipponbare/Kasalath cross and Nipponbare) were grown under soil moisture gradients with a line source sprinkler system. Three N fertilizer treatments were used; 25 (low), 75 (standard) and 150 kg N ha −1 (high) in 2009 and 60 (low), 120 (standard) and 180 kg N ha −1 (high) in 2011. Results Across varying N level treatments, there were no significant differences in any of the traits examined between the two genotypes under well-watered and severe drought stress conditions. In contrast, under MDS conditions (15–25 % w/w of soil moisture content (SMC) in 2009 and 17–25 % w/w of SMC in 2011), CSSL50 showed greater DMP than Nipponbare. The difference, however, varied with N level treatments since CSSL50’s greater root system development under MDS, was more pronounced at standard and high N levels than at low N level than it was for Nipponbare. Conclusions N application enhanced the expression of plasticity in root system development at standard and high N levels as compared with low N level under MDS conditions, which contributed to the maintenance of DMP.

Description: Background and aims Mechanisms of Mn accumulation and toxicity in and around trichomes on the Ni hyperaccumulator Alyssum murale were investigated. Methods Plants were grown aeroponically with variable amounts of Mn and Ni. Total metals were determined and electron microprobe analysis (EMPA) and synchrotron-based micro x-ray fluorescence (μ-SXRF) spectroscopy were used to evaluate metal distribution. Synchrotron techniques (μ-XANES, μ-EXAFS) along with infrared spectroscopy (DRIFT) were used to determine Mn speciation. Results At lower Mn concentrations or when grown together with Ni, Mn is confined to the trichome basal compartment in the +2 oxidation state in a complex with phosphate. At tissue concentrations 〉1,150 μg g −1 Mn-rich lesions develop around some trichomes in which greater amounts of Mn 3+ is found. Conclusions Mn is preferentially stored in trichomes on the plant surface which at higher concentrations enters the cell wall or apoplastic space of neighboring cells resulting in the formation of brown reaction products and oxidized Mn species. We propose a mechanism by which lesion formation and oxidized Mn species around some trichomes is possibly due to induction of the peroxidase system by excess Mn, triggering the accumulation of toxic phenoxy radicals and Mn 3+ .

Description: Background Aluminum (Al) toxicity has limited the productivity and expansion of cereal crops on acid soils; however, a number of plant species or cultivars have developed different strategies for detoxifying aluminum both internally and externally. Scope This review focuses on recent progress on molecular mechanisms of Al tolerance in gramineous plants. Conclusions A common mechanism in all gramineous plants is the secretion of organic acid anions (citrate and malate) from the roots. Genes belonging to ALMT (for Al uminum-activated m alate t ransporter) and MATE ( M ultidrug a nd t oxic compound e xtrusion) family involved in the secretion have been identified in several plant species; however, different plant species show different gene expression patterns including Al-induction, spatial and temporal expression, and tissue localization. Furthermore, the mechanisms regulating the gene expression also differ with plant species, which are achieved by increased tandem repeated element, increase of copy number, insertion of transposon, or alteration of cis-acting element. In addition to these common Al exclusion mechanisms, rice as a highly Al-tolerant species has developed a number of other mechanisms for detoxification of Al. A transcription factor for Al tolerance ART1 identified in rice regulates at least 30 genes implicated in internal and external detoxification of Al. These multiple genes may contribute to the high Al tolerance of rice. In the future, regulation mechanisms of Al-tolerance genes need to be further investigated.

Description: Aims This study aimed to analyse the effect of phosphorus (P) nutritional status on wheat leaf surface properties, in relation to foliar P absorption and translocation. Methods Plants of Triticum aestivum cv. Axe were grown with three rates of root P supply (equivalent to 24, 8 and 0 kg P ha −1 ) under controlled conditions. Foliar P treatments were applied and the rate of drop retention, P absorption and translocation was measured. Adaxial and abaxial leaf surfaces were analysed by scanning and transmission electron microscopy. The contact angles, surface free energy and work-of-adhesion for water were determined. Results Wheat leaves are markedly non-wettable, the abaxial leaf side having some degree of water drop adhesion versus the strong repulsion of water drops by the adaxial side. The total leaf area, stomatal and trichome densities, cuticle thickness and contact angles decreased with P deficiency, while the work-of-adhesion for water increased. Phosphorous deficient plants failed to absorb the foliar-applied P. Conclusions Phosphorous deficiency altered the surface structure and functioning of wheat leaves, which became more wettable and had a higher degree of water drop adhesion, but turned less permeable to foliar-applied P. The results obtained are discussed within an agronomic and eco-physiological context.

Description: Background and aims Legumes of the South African genus Lessertia , along with their microsymbionts, were introduced into the Western Australia wheatbelt. They achieved poor establishment followed by weak summer survival. This was caused in part by low levels of nodulation with the inoculant strains, and by ineffective nodulation with naturalized strains –an example of non-selective nodulation. The aims of this work were to assess Lessertia spp. symbiotic promiscuity, to study the effect of increased doses of an effective inoculant strain (WSM3565) with L. herbacea, and to study the competitive ability and symbiotic performance of different Mesorhizobium strains nodulating L. diffusa. Methods A glasshouse experiment was set up to evaluate the ability of L. diffusa , L. capitata , L. herbacea and L. excisa to nodulate with inoculants under current use in Western Australia. To assess competitive ability two field experiments were set up at Karridale, Western Australia. L. herbacea was inoculated with the strain WSM3565 at different doses and L. diffusa was inoculated with ten different Mesorhizobium strains. Rhizobia were re-isolated from nodules and their identity confirmed through PCR fingerprinting and sequencing of their partial dnaK . Results There were differences in promiscuity between different Lessertia spp., where L. herbacea proved to be highly promiscuous under controlled conditions. Increasing the inoculation dose of L. herbacea with WSM3565 did not improve establishment and survival of the legume in the field. Although WSM3565 nodule occupancy improved from 28 to 54 % with higher doses of inoculation, none of the treatments increased L. herbacea yield over the inoculated control. The inoculation of L. diffusa with the strains WSM3598, 3636, 3626 and 3565 resulted in greater biomass production than the uninoculated control. These strains were able to outcompete resident rhizobia and to occupy a high (〉60 %) proportion of lateral root nodules. The naturalised strains that achieved nodulation were identified as R. leguminosarum. Conclusion The high numbers of resident rhizobia and their ability to rapidly nodulate Lessertia spp . are likely to be the main reasons for the low nodule occupancy achieved by some effective inoculant strains with L. diffusa and L. herbacea . Strains WSM 3636 and 3598 were very competitive on nodule occupancy and together with WSM 3565, WSM 3612 and WSM3626, effective on nodule formation and plant growth of L. diffusa despite the high numbers of resident soil rhizobia. These strains and L. diffusa have potential to be introduced as exotic legumes species and rhizobia strains to Western Australia.

Description: Aims This study analyzed the extent to which root exudates diffuse from the root surface towards the soil depending on topsoil and subsoil properties and the effect of arbuscular mycorrhizal fungal hyphae on root-derived C distribution in the rhizosphere. Methods Alfalfa was grown in three-compartment pots. Nylon gauze prevented either roots alone or roots and arbuscular mycorrhizal fungal hyphae from penetrating into the rhizosphere compartments. 14 CO 2 pulse labeling enabled the measurement of 14 C-labeled exudates in dissolved (DOC) and total organic carbon (TOC) in the rhizosphere, distributed either by diffusion alone or by diffusion, root hair and hyphal transport. Results Root exudation and microbial decomposition of exudates was higher in the rhizosphere with topsoil compared to subsoil properties. Exudates extended over 28 mm (DOC) and 20 mm (TOC). Different soil properties and mycorrhization, likely caused by the low arbuscular mycorrhizal colonization of roots (13 ± 4 % (topsoil properties) and 18 ± 5 % (subsoil properties)), had no effect. Conclusions Higher microbial decomposition compensated for higher root exudation into the rhizosphere with topsoil properties, which resulted in equal exudate extent when compared to the rhizosphere with subsoil properties. Higher 14 C activity used for labeling compared with previous studies enabled the detection of low exudate concentrations at longer distances from the root surface.

Description: Background and aims The ionome (elemental composition) of grassland species has rarely been studied at the level of individual organs and little is known about effects of soil chemical properties on the ionome. Using the model oxalate plant Rumex obtusifolius, we asked how its biomass production and the distribution of elements between its organs is affected by soil chemical properties. Methods We established a pot experiment with R. obtusifolius planted in acidic non-contaminated control and in slightly acidic and alkaline soils anthropogenically contaminated by the risk elements As, Cd, Pb, and Zn. Both contaminated soils were untreated and treated by lime and superphosphate. We determined biomass production and the concentrations of elements in its organs. Results Biomass production was negatively related to the mobility of micro- and risk elements. Restricted transport of micro- and risk elements from belowground organs into leaves was recorded in untreated contaminated soils. In both lime-treated soils and in superphosphate-treated alkaline soil, elevated transport of micro- and risk elements from belowground organs into leaves was recorded in comparison to untreated contaminated soils. The lowest concentrations of micro- and risk elements were recorded in stems and seeds, followed by belowground organs and leaves. Conclusions R. obtusifolius is an As-, Cd-, Pb-, and Zn-excluder and is sensitive to high availability of micro- and risk elements in the soil. Soil chemical properties affect the distribution of essential elements within the plant greatly.

Description: Background and aims Nitrogen fixation associated with cryptogams is potentially very important in arctic and subarctic terrestrial ecosystems, as it is a source of new nitrogen (N) into these highly N limited systems. Moss-, lichen- and legume-associated N 2 fixation was studied with high frequency (every second week) during spring, summer, autumn and early winter to uncover the seasonal variation in input of atmospheric N 2 to a subarctic heath with an altered climate. Methods We estimated N 2 fixation from ethylene production by acetylene reduction assay in situ in a field experiment with the treatments: long- vs. short-term summer warming using plastic tents and litter addition (simulating expansion of the birch forest). Results N 2 fixation activity was measured from late April to mid November and 33 % of all N 2 was fixed outside the vascular plant growing season (Jun–Aug). This substantial amount underlines the importance of N 2 fixation in the cold period. Warming increased N 2 fixation two- to fivefold during late spring. However, long-term summer warming tended to decrease N 2 fixation outside the treatment (tents present) period. Litter alone did not alter N 2 fixation but in combination with warming N 2 fixation increased, probably because N 2 fixation became phosphorus limited under higher temperatures, which was alleviated by the P supply from the litter. Conclusion In subarctic heath, the current N 2 fixation period extends far beyond the vascular plant growing season. Climate warming and indirect effects such as vegetation changes affect the process of N 2 fixation in different directions and thereby complicate predictions of future N cycling.

Description: Background and aims The introduction of Acacia mangium in Eucalyptus urophylla x grandis stands improves wood production on poor sandy soils of coastal plains of the Congo. We assessed the impact of A. mangium plantations in pure stands and in mixture with eucalypt trees on the physico-chemical properties of the soil after one rotation. Methods Bulk densities, N, C, available P and pH were determined on soil sampled in the pure acacia (100A), pure eucalypt (100E) and mixed-species (50A:50E) stands. N and P were determined in aboveground litters and in leaves, bark and wood of trees. Results N and C concentrations were higher in 50A:50E than in 100A and 100E in the top soil layer. The pH was lower in 100A and higher in 100E than in 50A:50E. The available P was lower in 50A:50E than in 100A and 100E. Leaf N was lower in 50A:50E than in 100A for acacia, and higher than in 100E for eucalypt. Leaf P was similar for acacia but higher for eucalypt in 50A:50E than in 100E. In contrast to P, the amount of N in aboveground litterfall increased with the proportion of acacia in the stand. Conclusions The introduction of acacia trees in eucalypt plantations increased C and N contents of the soil but decreased the available P content in the mixed-species stand. This may be related to a higher uptake of P needed to maintain the N:P stoichiometry in eucalypt leaves.

Description: Background and purpose To date, very few studies have investigated the effects of litter decomposition on gross nitrogen (N) transformations and N retention in subtropical forest soils. In this study, six forest soils were taken from two contrasting forest types (broad-leaved vs. coniferous) in the humid subtropical zones of China to investigate the effects of litter decomposition on gross N transformations. Methods A 15  N tracing experiment was conducted to investigate the effects of litter decomposition (at a rate of 0.5 % w/w) on soil gross N transformations rates in broad-leaved and coniferous forests. Results Litter decomposition enhanced gross N mineralization and NH 4 + immobilization rates by 45.9–79.0 % and 553–563 %, respectively. There was a shift from net N mineralization to net N immobilization in each of the forest soils, which was due to litter decomposition. In contrast, gross nitrification rates were unaffected by litter decomposition for each of the forest soils, while gross NO 3 − immobilization rates were stimulated significantly by litter decomposition in broad-leaved forest soils but not in coniferous forest soils. On average, 39.4 % of the total NO 3 − produced was immobilized into organic-N in broad-leaved forest soils due to litter decomposition. Therefore, the decrease in net nitrification rates caused by litter decomposition was attributed to increasing gross NO 3 − immobilization rates rather than decreasing gross nitrification rates. During 15 days of incubation, the decomposition of litter increased cumulative N 2 O emissions by 55–76 % and 100–640 % in broad-leaved forest and coniferous forest soils, respectively, but there was no effect on the cumulative NO emissions for both forest soil types. Conclusions The combined results suggest that the decomposition of litter stimulates N 2 O emissions but reduces NH 4 + and NO 3 − accumulation in forest soils, and thus a delay in N availability for plant N uptake or leaching.

Description: Aims Potatoes are a globally important source of food whose production requires large inputs of fertiliser and water. Recent research has highlighted the importance of the root system in acquiring resources. Here measurements, previously generated by field phenotyping, tested the effect of root size on maintenance of yield under drought (drought tolerance). Methods Twelve potato genotypes, including genotypes with extremes of root size, were grown to maturity in the field under a rain shelter and either irrigated or subjected to drought. Soil moisture, canopy growth, carbon isotope discrimination and final yields were measured. Destructively harvested field phenotype data were used as explanatory variables in a general linear model (GLM) to investigate yield under conditions of drought or irrigation. Results Drought severely affected the small rooted genotype Pentland Dell but not the large rooted genotype Cara. More plantlets, longer and more numerous stolons and stolon roots were associated with drought tolerance. Previously measured carbon isotope discrimination did not correlate with the effect of drought. Conclusions These data suggest that in-field phenotyping can be used to identify useful characteristics when known genotypes are subjected to an environmental stress. Stolon root traits were associated with drought tolerance in potato and could be used to select genotypes with resilience to drought.

Description: Background and Aims Soil treatment by anaerobic soil disinfestation (ASD) combined with soil solarization can effectively control soilborne plant pathogens and plant-parasitic nematodes in specialty crop production systems. At the same time, research is limited on the impact of soil treatment by ASD + solarization on soil fertility, crop performance and plant nutrition. Our objectives were to evaluate the response of 1) soil nutrients and 2) vegetable crop performance to ASD + solarization with differing levels of irrigation, molasses amendment, and partially-composted poultry litter amendment (CPL) compared to an untreated control and a methyl bromide (MeBr) + chloropicrin-fumigated control. Methods A 2-year field study was established in 2008 at the USDA-ARS U.S. Horticultural Research Lab in Fort Pierce, Florida, USA to determine the effectiveness of ASD as an alternative to MeBr fumigation for a bell pepper ( Capsicum annum L.)-eggplant ( Solanum melongena L.) double crop system. A complete factorial combination of treatments in a split-split plot was established to evaluate three levels of initial irrigation [10, 5, or 0 cm], two levels of CPL (amended or unamended), and two levels of molasses (amended or unamended) in combination with solarization. Untreated and MeBr controls were established for comparison to ASD treatments. Conclusions Results suggest that ASD treatment using molasses as the carbon source paired with solarization can be an effective strategy to maintain crop yields in the absence of soil fumigants. For both bell pepper and eggplant crops, ASD treatments with molasses as the carbon source had equivalent or greater marketable yields than the MeBr control. The application of organic amendments in ASD treatment (molasses or molasses + CPL) caused differences in soil nutrients and plant nutrition compared to the MeBr control that must be effectively managed in order to implement ASD on a commercial scale as a MeBr replacement.

Description: Background and aims The association of the legume Anthyllis vulneraria and the grass Festuca arvernensis, was found to be very efficient for the phytostabilisation of highly multi-metal contaminated mine tailings. Our objective was to quantify the contribution of Anthyllis inoculated with its symbiotic bacteria Mesorhizobium metallidurans to the soil N pool and to test whether a starter nitrogen fertilization may improve symbiotic nitrogen fixation and the growth of Festuca . Methods Plants of Festuca and of Anthyllis inoculated with M. metallidurans were grown separately during eight months in pots filled with mine contaminated soil. Estimation of the N fluxes was realized using 15  N isotopic methods. Results Starter N fertilization (28 kg N ha −1 ) improved symbiotic N 2 fixation and the growth of both species. Belowground N balance (N rhizodeposition – soil N uptake) of the non-fertilized Anthyllis at maturity was negative (−30.6 kg N ha −1 ). However, the amount of N derived from fixation, including above- and belowground parts, was 78.6 kg N ha −1 , demonstrating the ability of this symbiotic association to improve soil N content after senescence. Conclusions i) soil N enrichment by the N 2 -fixing symbiotic association occurs after plant senescence, when decaying leaves and shoots are incorporated into the soil; ii) application of a starter fertilization is an efficient solution to improve phytostabilisation of highly contaminated sites.

Description: Background and aims Aleppo pine ( Pinus halepensis Mill.) is a widely used species for restoring degraded semiarid areas, but its use for the revegetation of metal(loid) polluted soils has not been thoroughly investigated. The main goal of this research was to study the ecophysiological status and elemental composition of spontaneous populations of Pinus halepensis growing on mine tailings to assess their use in phytomanagement of mine spoils in semiarid climates. Methods Edaphic characteristics and the physiological (by stable isotopes) and nutritional status of pine trees were determined on mine tailings, in the metalloid-polluted surroundings and a non-polluted control area. Results Low soil phosphorus availability at the tailings was found to be a more important limiting factor for pine physiological performance than high soil metal(lloid)s concentrations. Foliar phosphorus concentrations showed a strong negative correlation with foliar sulphur concentrations along the studied transect. The carbon and oxygen isotopic composition (δ 13 C and δ 18 O) of pine needles indicated that trees at the tailings were less water stressed than those in surroundings or control areas. The low foliar δ 15 N of pines growing at the tailings was due to low soil fertility and/or a heavy reliance on symbiotic ectomycorrhizal fungi for nitrogen uptake. Conclusions The results of this study indicate that Pinus halepensis is a suitable tree species for the phytostablisation of neutral or slightly-alkaline mining wastes in semiarid environments, thanks to its drought hardiness and good adaptation to low soil fertility and salinity.

Description: Background and Aims Water solubility of zinc (Zn) fertilisers affects their plant availability. Further, simultaneous application of Zn and phosphorus (P) fertiliser can have antagonistic effects on plant Zn uptake. Arbuscular mycorrhizas (AM) can improve plant Zn and P uptake. We conducted a glasshouse experiment to test the effect of different Zn fertiliser materials, in conjunction with P fertiliser application, and colonisation by AM, on plant nutrition and biomass. Methods We grew a mycorrhiza-defective tomato genotype ( rmc ) and its mycorrhizal wild-type progenitor (76R) in soil with six different Zn fertilisers ranging in water solubility (Zn sulphate, Zn oxide, Zn oxide (nano), Zn phosphate, Zn carbonate, Zn phosphate carbonate), and supplemental P. We measured plant biomass, Zn and P contents, mycorrhizal colonisation and water use efficiency. Results Whereas water solubility of the Zn fertilisers was not correlated with plant biomass or Zn uptake, plant Zn and P contents differed among Zn fertiliser treatments. Plant Zn and P uptake was enhanced when supplied as Zn phosphate carbonate. Mycorrhizal plants took up more P than non-mycorrhizal plants; the reverse was true for Zn. Conclusions Zinc fertiliser composition and AM have a profound effect on plant Zn and P uptake.

Description: Aims and background The phosphorus (P) fertilizer value of organic materials (OM) such as plant residues or manure can be larger than that of mineral fertilizers in weathered soils. Recently, the diffusive gradients in thin films (DGT) technique was shown to better predict crop response to applied mineral P fertilizer among soils than established tests. The goal of this study is to evaluate the potential of the DGT technique to predict plant-available P in different soils amended with various qualities of OM. Methods In this study, maize was grown in a greenhouse on two Kenyan soils characterized by strong P sorption. Phosphorus was applied at various rates (deficient to adequate) as triple superphosphate (TSP) only, or at one intermediate P dose in a P-substitution trial with four different OM: farmyard manure (FYM) or residues of Tithonia diversifolia each at low or high P content. All soils were amended with adequate amounts of other nutrients. Next to the DGT technique, two established soil P tests (anion exchange membranes (AEM), and Olsen) were performed on incubated soils for all P treatments. Results Results show that the relative yield (% of maximum yield) to soil P test values correlated most strongly for DGT measured P concentrations, R 2  = 0.74, compared to Olsen (R 2  = 0.60) and AEM (R 2  = 0.62). Conclusions Results of this study demonstrate that DGT relates best with DM yields when soils are amended with a combination of TSP and OM compared to the established soil P tests Olsen and AEM.

Description: Aims Plantation forests are often assumed to have reduced biodiversity relative to unmanaged forests. However, existing knowledge is based on studies of rotation-aged tree crops. We investigated how Eucalyptus afforestation of agricultural land affected plant species composition and biodiversity across a range of plantation ages (1–10 years). We also studied whether the soil seed bank could contribute to regeneration of existing vegetation in such plantations. Methods We used a chronosequence approach to evaluate plant and seed species composition and diversity in forests and soil seed banks. We also quantified the similarity of seed banks and aboveground vegetation within plantation sites of a given age. Plantation sites were also compared to a nearby, mature pine forest. Results Total plant species number, density and diversity in Eucalyptus grandis plantations increased for the first 3 years plantation establishment, then stabilized or decreased for the next 1–2 years and then increase significantly over the following years. Species number and density in soil seed bank increased significantly with plantation age only after an initial 6-year decrease. Shannon–Wiener index of total species diversity did not significantly differ with plantation age. The understory vegetation and soil seed bank were dominated by pioneer species in the first 3 years, but intermediate-successional and shade-tolerant species gradually invaded as plantations developed further. After 7 years, E. grandis plantation understories were composed of mainly shade-tolerant species. Nevertheless, the diversity of the diversity of intermediate-successional in soil seed banks were higher than that of shade-tolerant species in soil seed banks at this age range (7–10 year). Among species successfully germinated from soil seed banks, 48 % were not found in the aboveground plant community. Similarities between the species in the soil seed bank and the aboveground vegetation were low for both plantation and control forests and did not significantly change with plantation ages. Conclusions E. grandis likely produces a changing microclimate during plantation development, which in turn drives composition and diversity dynamics in understory vegetation and soil seed banks after the afforestation of agricultural land. The first 4 years after plantation establishment is associated with lower plant and soil seed bank diversity, meriting a greater focus on biodiversity stabilization and possibly longer rotation periods.

Description: Aims Substantial amounts of VFG-compost are produced annually in Flanders. Our objective was to analyse the effects of VFG-compost applications in a common crop rotation. Methods Data from a long-term (1997 – present) field trial were analysed. Simulations with the RothC-model were performed to get a better insight into the dynamics of the underlying soil organic matter. Results VFG-compost applications (15 t.ha −1 3-yearly up to 45 t.ha −1 yearly) can replace a substantial part of the mineral nitrogen fertilisation. Nitrogen recovery rates ranged from 6 to 22 %. Plots fertilised according to the nitrogen advice had comparable yields, whether this advice had been provided (partially) through VFG-compost or not. Long-term VFG applications resulted in carbon accumulation in the top soil. The RothC-model gave a good prediction of the carbon change with low to moderate VFG applications, but tended to overestimate the carbon change with high applications. The simulation results indicated that the carbon accumulation was mainly due to an increase of the more resistant carbon fractions. In the long term, compost applications increased the nitrogen supplying capacity of the soil, as illustrated by the gradual increase of the mineral nitrogen stocks in spring over the years. Conclusions VFG-compost applications had a positive effect both on crop yields and soil organic matter. The RothC-model was used to simulate long-term effects, but its calibration should be improved for long-term compost applications.

Description: Background and aims Flooding stress is known to affect root growth and sugar metabolism in plants, but data are crucially missing for Cichorium intybus which stores inulin in its tap root. The aim of the present study was to quantify the impact of recurrent episodes of flooding stress on plant growth, water status, photosynthesis and sugar metabolism in relation to inulin synthesis and accumulation in roots of this species . Methods Plants were cultured for 25 weeks under controlled environmental conditions on a sand substrate in columns saturated with nutrient solution for periods of 2–3 weeks (starting on week 12) alternating with 7 days non-flooding periods. Plant growth, water status, photosynthesis-related parameters and sugar concentration and metabolism were monitored at regular intervals up to the end of the treatment. Key results Flooding increased the number of leaves but reduced net photosynthesis in relation to stomatal closure and decrease in PSII efficiency. The roots of flooded plants were shorter and larger than those of controls but fresh and dry weight were similar in the two situations. Reducing sugars and organic acids accumulated in the leaves while glucose, fructose, sucrose and 1-kestotriose accumulated in the roots. Sucrose synthase (EC 2.4.1.13) and invertase (EC 3.2.1.26) activities increased in both organs while sucrose-phosphate-synthase activity (EC 2.4.1.14) remained unaffected by flooding. Inulin synthesis was delayed in flooded roots and its mean degree of polymerization (DP) was reduced as a consequence of fructan:fructan 1-fructosyltransferase (1-FFT, EC 2.4.1.100) inhibition. Conclusions Cichorium intybus is able to cope with intermittent episodes of flooding and modify organ shape without any effect on final weight. Quantity of inulin produced per plant remained unaffected but the quality of inulin (mean DP) decreased as a consequence of flooding.

Description: Background and aims The duration of soil organic carbon (SOC) sequestration in agricultural soils varies according to soil management, land-use history and soil and climate conditions. Despite several experiments have reported SOC sequestration with the adoption of no-tillage (NT) in Mediterranean dryland agroecosystems scarce information exists about the duration and magnitude of the sequestration process. For this reason, 20 years ago we established in northeast Spain a NT chronosequence experiment to evaluate SOC sequestration duration under Mediterranean dryland conditions. Methods In July 2010 we sampled five chronosequence phases with different years under NT (i.e., 1, 4, 11, and 20 years) and a continuous conventional tillage (CT) field, in which management prevailed unchanged during decades. Soil samples were taken at four depths: 0–5, 5–10, 10–20 and 20–30 cm. The SOC stocks were calculated from the SOC concentration and soil bulk density. Furthermore, we applied the Century ecosystem model to the different stages of the chronosequence to better understand the factors controlling SOC sequestration with NT adoption. Results Differences in SOC stocks were only found in the upper 5 cm soil layer in which 4, 11 and 20 years under NT showed greater SOC stocks compared with 1 year under NT and the CT phase. Despite no significant differences were found in the total SOC stock (0–30 cm soil layer) there was a noteworthy difference of 5.7 Mg ha −1 between the phase with the longest NT duration and the phase under conventional tillage. The maximum annual SOC sequestration occurred after 5 years of NT adoption with almost 50% change in the annual rate of SOC sequestration. NT sequestered SOC over the 20 years following the change in management. However, more than 75% of the total SOC sequestered was gained during the first 11 years after NT adoption. The Century model predicted reasonably well SOC stocks over the NT chronosequence. Conclusions In Mediterranean agroecosystems, despite the continuous use of NT has limited capacity for SOC sequestration, other environmental and agronomic benefits associated to this technique may justify the maintenance of NT over the long-term.

Description: Aim Root biomass has long been under-represented in biodiversity–ecosystem functioning studies, despite its dominance in biomass in many arid and semi-arid ecosystems. We aimed to explore the multivariate control over root biomass by plant diversity, together with other biotic and abiotic factors and to evaluate the relative importance of these factors. Methods Above- and below-ground traits of 13 communities and soil properties were measured in semi-arid grasslands on the Loess Plateau, China. Structural equation modeling (SEM) was used to evaluate the relative importance of the community and soil characteristics, emphasizing the direct and indirect effects of plant diversity on root biomass. Results Significant indirect effects of plant species richness on root biomass were found, although no direct correlation was detected between them. In the indirect pathways, plant species richness showed a positive effect on soil total nitrogen, but a significant negative influence on soil total carbon. Soil total nitrogen and plant diversity had the largest and smallest total effect respectively on root biomass in the model. Conclusions Plant species richness was not the strongest determinant of root biomass but had a significant indirect effect, mediated through soil total carbon and nitrogen. This study suggests that greater plant species richness, through a positive influence on soil total nitrogen, may indirectly promote root carbon stock.

Description: Background and Aims Under limited moisture conditions, roots can play an outstanding role with respect to yield stability by effective absorption of water from soil. A targeted integration of root traits into plant breeding programs requires knowledge on the existing root diversity and access to easy and cost-effective methods. This study aimed to assess wheat root diversity, root properties in relation to water regime, and the efficiency of root capacitance for in situ screening. Methods Root morphological, anatomical properties and root capacitance of wheat species from different ploidy levels were studied under field conditions in 2 years contrasting in water regime. Soil water content was weekly measured. Results Significant genotypic differences were observed for most root traits. The investigated genotypes exploited different strategies to maximize soil water depletion, e.g. high topsoil root length density, low tissue mass density, high specific root length, deep rooting and looser xylem vessels. Multivariate statistics of root traits revealed an acceptable genotypic differentiation according to regional origin, genetics and capacity to extract soil water. Conclusions Under supply-driven environments, dehydration avoidance via water uptake maximization can be achieved through high topsoil rooting density. In this regard, root capacitance can be useful for in situ screening.

Description: Background and Aims For plants growing in living walls, the growth potential is correlated to the roots ability to utilize resources in all parts of the growing medium and thereby to the spatial root distribution. The aim of the study was to test how spatial root distribution was affected by growing medium, planting position and competition from other plants. Methods Five species ( Campanula poscharskyana cv. ‘Stella’, Fragaria vesca cv. ‘Småland’, Geranium sanguineum cv. ‘Max Frei’, Sesleria heufleriana and Veronica officinalis cv. ‘Allgrün’) were grown in three growing media (coir and two of rockwool) in transparent boxes under greenhouse conditions. Root frequency was registered and the activity of individual root systems was studied via 15 N uptake and plant dry weight was measured. Results Plants in coir had stronger root growth in all parts of the medium than plants in rockwool. Upwards root growth was limited for plants in the middle or lower parts of the medium and 15 N measurements confirmed that only plants in the bottom of the box had active roots in the bottom of the medium. The species differed in root architecture and spatial root distribution. Conclusions The choice of growing medium, plant species and planting position is important for a living wall as it affects the spatial root growth of the plants.

Description: Background and aims The Root is an important plant organ and has high heterogeneity; how it responds to global warming is yet to be answered. This study examined the growth and physiological responses of fine roots to warming around the non-growing season. Methods Plants from 4-year-old Picea asperata were grown under experimental warming conditions. A detailed investigation was conducted by measuring biomass, triphenyltetrazolium chloride (TTC) reducing capacity, carbon (C) and nitrogen (N) concentration, non-structural carbohydrate (NSC) of the primal five branch order roots in early (April) and late (September) growing seasons as well as in the non-growing season (December). Results Warming promoted fine root growth in April and fine root turnover was mostly in the first four orders. It decreased root C, N concentration in the early and late growing seasons but increased N concentration in the non-growing season. Moreover, it increased NSC concentration (especially soluble sugar) in April but decreased its concentration (soluble sugar and starch) in December. TTC reducing capacity in April was higher than in the other 2 months. Conclusions The effect of warming on tree roots varied with its branch order and month. The lower order (first three or four order, in general) roots were sensitive to warming, especially in April (early part of growing season) and December (non-growing season). Warming accelerated the carbon input from root to soil. It is indicated that any changes in winter temperatures could alter the sink strength of terrestrial ecosystems considerably. Moreover, TTC reducing capacity could reflect more information about root, but it was more sensitive than N concentration.

Description: Aims Plant roots play an important role in the stability of the slope. The efficiency of the vegetation in the slope stability relies on the planting layout on the slope. Vegetation located at the upper, middle, and lower slopes is investigated to determine the influence of the spatial layout of planting on the stability of slopes. Additionally, the role of plant roots in the mechanical mechanism of the vegetated slope is studied. Methods A simple root system architecture with one tap root and four lateral roots is selected, and 3D root structure is integrated with the soil. The 3D finite element analysis is used to model the stability of vegetated slopes. Results Soil arching takes place in the soil between root systems. As the spacing between root system increases, the effect of vegetation on the slope stability decreases. The effect of vegetation at the upslope and mid-slope on the safety factor of the slope is better than that at the downslope if the plant root system penetrates into the firm ground. Conclusions Assessment of the stability of vegetated slopes may be affected by the root structure pattern, the relationship between the root system and the firm ground, and the modeling method of the root system in the ground.

Description: Background and aims It is of practical relevance to know how much beech must be admixed to pure spruce stands in order to increase litter decomposition and associated nutrient cycling, since the formation of thick organic layers is commonly ascribed to the recalcitrance of spruce needles. We addressed the impact of tree species mixture within forest stands and within litter on mass loss and nutritional release from litter. Methods Litter decomposition was measured in three adjacent stands of pure spruce ( Picea abies ), mixed beech-spruce and pure beech ( Fagus sylvatica ) on a nutrient-rich site and a nutrient-poor site over a 2-year period using litterbags which were filled with five different mixtures of beech and spruce litter. Results Mass loss of beech litter was not higher than mass loss of spruce litter. Decay was primarily affected by tree species composition of the incubation stand and was faster in (mixed) beech forests stands than in spruce forests, while the influence of litter species and their mixtures on decay rates was small. Net transfers of nutrients between the two litter species (direct effects) in the mixed bags were minimal, since initial beech and spruce litter did not have different litter quality. However, in a few cases indirect effects (e.g., changing decomposer abundance and activity) caused non-additive patterns for the totals within the mixed bags, hastening decomposition within the first year. Conclusions Greater accumulation of litter in spruce compared to beech stands is not a consequence of the inherent recalcitrance of needles. Adverse environmental conditions in spruce stands retard decomposition. Indirect effects on decomposition caused by stand mixture are not mimicked by litter mixtures within mesh bags.

Description: Aims Soil salinity can cause salt plant stress by reducing plant transpiration and yield due to very low osmotic potentials in the soil. For predicting this reduction, we present a simulation study to (i) identify a suitable functional form of the transpiration reduction function and (ii) to explain the different shapes of empirically observed reduction functions. Methods We used high resolution simulations with a model that couples 3D water flow and salt transport in the soil towards individual roots with flow in the root system. Results The simulations demonstrated that the local total water potential at the soil-root interface, i.e. the sum of the matric and osmotic potentials, is for a given root system, uniquely and piecewise linearly related to the transpiration rate. Using bulk total water potentials, i.e. spatially and temporally averaged potentials in the soil around roots, sigmoid relations were obtained. Unlike for the local potentials, the sigmoid relations were non-unique functions of the total bulk potential but depended on the contribution of the bulk osmotic potential. Conclusions To a large extent, Transpiration reduction is controlled by water potentials at the soil-root interface. Since spatial gradients in water potentials around roots are different for osmotic and matric potentials, depending on the root density and on soil hydraulic properties, transpiration reduction functions in terms of bulk water potentials cannot be transferred to other conditions, i.e. soil type, salt content, root density, beyond the conditions for which they were derived. Such a transfer could be achieved by downscaling to the soil-root interface using simulations with a high resolution process model.

Description: Background and aims The high metal bioavailability and the poor conditions of mine soils yield a low plant biomass, limiting the application of phytoremediation techniques. A greenhouse experiment was performed to evaluate the effects of organic amendments on metal stabilization and the potential of Brassica juncea L. for phytostabilization in mine soils. Methods Plants were grown in pots filled with soils collected from two mine sites located in Central Spain mixed with 0, 30 and 60 t ha −1 of pine bark compost and horse- and sheep-manure compost. Plant biomass and metal concentrations in roots and shoots were measured. Metal bioavailability was assessed using a rhizosphere-based method ( rhizo ), which consists of a mixture of low-molecular-weight organic acids to simulate root exudates. Results Manure reduced metal concentrations in shoots (10–50 % reduction of Cu and 40–80 % of Zn in comparison with non-amended soils), bioconcentration factor (10–50 % of Cu and 40–80 % of Zn) and metal bioavailability in soil (40–50 % of Cu and 10–30 % of Zn) due to the high pH and the contribution of organic matter. Manure improved soil fertility and was also able to increase plant biomass (5–20 times in shoots and 3–30 times in roots), which resulted in a greater amount of metals removed from soil and accumulated in roots (increase of 2–7 times of Cu and Zn). Plants grown in pine bark treatments and in non-amended soils showed a limited biomass and high metal concentrations in shoots. Conclusions The addition of manure could be effective for the stabilization of metals and for enhancing the phytostabilization ability of B. juncea in mine soils. In this study, this species resulted to be a potential candidate for phytostabilization in combination with manure, differing from previous results, in which B. juncea had been recognized as a phytoextraction plant.

Description: Background and aims Volatile organic compounds (VOCs) released into the air from eucalyptus have putative roles in chemical communications. But the types and concentrations released in nature, as well as the ecological functions of VOCs in soil water, have not been adequately investigated to date. Methods We developed some effective methods for the extraction of VOCs released by root exudation, foliage and leaf litter leaching, and leaf litter decomposition, into water extracts in the laboratory or from field soil around Eucalyptus urophylla . The VOCs were determined by GC-MS. Lolium multiflorum Lam. (annual ryegrass) and Bidens pilosa (cobbler’s pegs) were selected to test the phytotoxic effects of VOCs in soil water released from E. urophylla grown under natural conditions. Results Fourteen VOCs in soil water, released by foliage and leaf litter leaching and leaf litter decomposition, were identified and quantified. But we did not identify any VOCs from root exudates. When the concentrations of VOCs were reconstituted to mimic the soil conditions, the laboratory bioassays showed that seed germination and seedling growth of the tested plants were significantly inhibited. Conclusions VOCs in soil water were phytotoxic when they had been released by foliage and leaf litter leaching and leaf litter decomposition from E. urophylla .

Description: Background and aims A soil fertility gradient, ranging from infertile to highly fertile soils, may define whether or not a plant will establish and spread at a site. We evaluated whether or not such a fertility gradient exists for Rosa multiflora Thunb., a nonnative invasive shrub, and Kalmia latifolia L., a native problem shrub, in closed-canopy forests of the eastern U.S. Methods We sampled soil and vegetation at the regional scale, along four randomly located 1-km transects in 70+ year-old undisturbed forests in each of three national forests in Ohio, Pennsylvania and West Virginia. We also sampled soil, vegetation and leaf tissue at the local scale, from ten individual shrubs of each species in each national forest. Results Regional analyses showed a significant fertility gradient with Ohio being the most fertile and West Virginia the least. Soil fertility was associated with pH (most acidic in West Virginia and least acidic in Ohio) and elevation (highest in West Virginia and lowest in Ohio). At the local level, R. multiflora was associated with soil Ca:Al ratios greater than 0.5, and K. latifolia was associated with Ca:Al ratios less than 0.3. Rosa multiflora foliage contained higher concentrations of Ca, Mg, and K than K. latifolia , while K. latifolia foliage contained higher concentrations of Mn and Zn. Conclusions Our research documents the importance of soil fertility as a predictor of the establishment of invasive and expansive shrubs. This study further shows that R. multiflora can establish and spread across a broader range of soil conditions than K. latifolia .

Description: Aims Phosphorus resources have to be managed sustainably and therefore the recycling of P from waste streams is essential. A thermo-chemical recycling process has been developed to produce a P fertilizer from sewage sludge ash (SSA) but its plant availability is unknown. Methods Two SSA products prepared with either CaCl 2 (SSACa) or MgCl 2 (SSAMg) as chemical reactant during the thermal treatment were mixed with three soils previously labeled with 33 P. Reference treatments with water-soluble P added at equal amounts of total P were included. The transfer of P from SSACa and SSAMg to Lolium multiflorum or P pools of sequentially extracted soil-fertilizer incubations were quantified. Results The shoot P uptake from SSAMg was higher than from SSACa. For SSAMg the relative effectiveness compared to a water-soluble P fertilizer was 88 % on an acidic and 71 % on a neutral soil but only 4 % on an alkaline soil. The proportion of P derived from the fertilizer in the plant and in the first two extraction pools of soil-fertilizer incubations were strongly correlated, suggesting that it is sufficient to conduct an incubation study to obtain robust information on plant P availability. Conclusions We conclude that under acidic to neutral conditions SSAMg presents an appropriate alternative to conventional P fertilizers and the dissolution of P from SSAMg seems to be governed by protons and cations in the soil solution.

Description: Aims Forests induce a mechanical reinforcement of soil, generally quantified in terms of additional root cohesion ( c r ), which decreases due to root decay after felling. The aim of this work is providing new field data on soil reinforcement by roots after trees cutting. Methods The present work investigated c r decay in a mixed Silver Fir-Norway Spruce ( Abies alba Mill. Picea abies (L.) Karst.) stand in the Italian Alps over a period of 3 years after felling by monitoring the two c r driving variables: root tensile resistance and root density. Results Results showed that a significant difference in root resistance occurred only 3 years after felling, whereas the decrease in the number of roots was significant in the second year. The degradation process was more rapid in shallower layers and for thinner roots, as a consequence of the pattern of biological activity rate. The reduction of c r after felling was, for a reference profile depth of 70 cm, 55 % in the first 2 years and another 16 % in the third year. Conclusions The findings of this study, providing new data on the decrease of c r after felling, can be introduced into geotechnical models allowing a better estimation of the stability of forest hillslopes.

Description: Background & aims Despite increasing knowledge of the interference of allelopathic rice with barnyardgrass mediated by allelochemicals, the interference mechanisms are still being elucidated. Here we test whether the interference of allelopathic rice with barnyardgrass may be interpreted from the perspective of plant-soil feedback. Methods We grew barnyardgrass in the soil previously grown with allelopathic rice at the seedling and mature stages in relation to monoculture and mixed-culture and examined the performance of barnyardgrass. We quantified soil allelochemicals and analyzed soil nutrients and microbial communities. Results Barnyardgrass biomass in soil trained by allelopathic rice PI312777 seedlings was reduced significantly when compared with non-allelopathic rice Liaojing-9 and barnyardgrass seedlings. The performance differences were strengthened by mixed-culture with allelopathic rice seedlings or when incubated with their root exudates and trained soils. In contrast, increased biomass of barnyardgrass in the allelopathic rice soil was observed at the mature stage. At the seedling stage, allelochemical concentrations were much higher in the allelopathic than in the non-allelopathic rice soils. At the mature stage, however, allelochemicals were not detected in the soils. Soil nutrients and phospholipid fatty acids profiles showed that negative feedback at the seedling stage was independent of allelochemicals and microbial communities while positive feedback at the mature stage was more related to nutrients than to allelochemicals and microbial communities. Conclusions Plant-soil feedback contributes to the interference of allelopathic rice with barnyardgrass, and allelochemical context alters plant-soil feedback at different growth stages.

Description: Background and aims Biocrusts are communities of cyanobacteria, algae, bryophytes, and lichens that influence plants and soils worldwide. In the Province Lands sand dunes of Cape Cod, algal biocrusts coexist with extensive bryophyte and lichen mats. The relationship between biocrusts, moss and lichen mats, and plants at this site has never been evaluated. Methods We evaluated the effects of algal biocrusts and moss and lichen mats on soil moisture, plant productivity, and plant tissue water and nutrients of two dune plants , Deschampsia flexuosa and Morella pensylvanica . Results Soil moisture was highest under lichen-moss mats and lowest under moss-only mats. Algae-only biocrusts and bryophyte and lichen mats significantly affected seedling survivorship, height, biomass, root growth, and tissue water and micronutrients. When compared to controls, algae-only biocrusts and moss-only mats increased seedling survivorship and vigor, while lichen-moss mats decreased these plant responses. However, all biocrusts and mats tended to decrease plant productivity compared to controls. Conclusions Biocrusts and mats play an important role in plant performance at this site, primarily via their effects on soil moisture, and possibly through their effects on plant tissue nutrients. Plants growing among biocrusts and mats at this site may experience a tradeoff between survivorship and productivity.

Description: Background and aims Inoculation of legumes at sowing with rhizobia has arguably been one of the most cost-effective practices in modern agriculture. Critical aspects of inoculant quality are rhizobial counts at manufacture/registration and shelf (product) life. Methods In order to re-evaluate the Australian standards for peat-based inoculants, we assessed numbers of rhizobia (rhizobial counts) and presence of contaminants in 1,234 individual packets of peat–based inoculants from 13 different inoculant groups that were either freshly manufactured or had been stored at 4 °C for up to 38 months to determine (a) rates of decline of rhizobial populations, and (b) effects of presence of contaminants on rhizobial populations. We also assessed effects of inoculant age on survival of the rhizobia during and immediately after inoculation of polyethylene beads. Results Rhizobial populations in the peat inoculants at manufacture and decline rates varied substantially amongst the 13 inoculant groups. The most stable were Sinorhizobium , Bradyrhizobium and Mesorhizobium with Rhizobium , particularly R. leguminosarum bv. trifolii the least stable. The presence of contaminants at the 10 −6 level of dilution, i.e. 〉log 6.7 g −1 peat, reduced rhizobial numbers in the stored inoculants by an average of 37 %. Survival on beads following inoculation improved 2–3 fold with increasing age of inoculant. Conclusions We concluded that the Australian standards for peat-based rhizobial inoculants should be reassessed to account for the large differences amongst the groups in counts at manufacture and survival rates during storage. Key recommendations are to increase expiry counts from log 8.0 to log 8.7 rhizobia g −1 peat and to have four levels of inoculant shelf life ranging from 12 months to 3 years.

Description: Aims The goal of this study was to investigate the structure and functional potential of microbial communities associated with healthy and diseased tomato rhizospheres. Methods Composition changes in the bacterial communities inhabiting the rhizospheric soil and roots of tomato plants were detected using 454 pyrosequencing. Microbial functional diversity was investigated with BIOLOG technology. Results There were significant shifts in the microbial composition of diseased samples compared with healthy samples, which had the highest bacterial diversity. The predominant phylum in both diseased and healthy samples was Proteobacteria , which accounted for 35.7–97.4 % of species. The class Gammaproteobacteria was more abundant in healthy than in diseased samples, while the Alphaproteobacteria and Betaproteobacteria were more abundant in diseased samples. The proportions of pathogenic Ralstonia solanacearum and Actinobacteria species were also elevated in diseased samples. The proportions of the various bacterial populations showed a similar trend both in rhizosphere soil and plant roots in diseased versus disease-free samples, indicating that pathogen infection altered the composition of bacterial communities in both plant and soil samples. In terms of microbial activity, functional diversity was suppressed in diseased soil samples. Soil enzyme activity, including urease, alkaline phosphatase and catalase activity, also declined. Conclusions This is the first report that provides evidence that R. solanacearum infection elicits shifts in the composition and functional potential of microbial communities in a continuous-cropping tomato operation.

Description: Aims The interactive effects of enhanced nitrogen (N) deposition and ultraviolet-B (UV-B) radiation on litter decomposition are still unknown. The aims are to test whether the interactive effects of the two environmental factors on litter decomposition and nutrient loss are stronger than that of each factor alone. Methods Experiment included five treatments: elevated UV-B radiation (UV-B, 10 % enhancement), low N addition (N1, 30 kg N ha −1  year −1 ), high N addition (N2, 60 kg N ha −1  year −1 ), the two combined treatments of the two factors (UV-B+N1 and UV-B+N2), and an unmanipulated control. Results The annual decomposition rates under combination of UV-B and N addition significantly decreased compared with that under UV-B and N additions for Pinus massoniana , and did also compared with that under UV-B but did not significantly differ with N additions for Cyclobalanopsis glauca . Negative effects of N additions alone on lignin degradation and P loss were partly offset but negative effect on N loss was further amplified when was combined with UV-B. Conclusions The combination of N deposition and UV-B radiation on litter decomposition and nutrient loss was significantly different from that of each factor alone without a general response pattern of decomposition, and was regulated by litter chemistry.

Description: Background and aims Many previous studies have evaluated aboveground–heterotrophic belowground interactions such as plant-soil feedbacks, plant-mycorrhizal fungi associations or plant-actinorhizal symbioses. However, few studies have used biocrusts, which are specialized soil communities of autotrophic cyanobacteria, mosses, lichens and non-photosynthetic fungi and bacteria that are prevalent in drylands worldwide. These communities largely influence ecosystem functioning, and can be used as a model system for studying above-belowground interactions. In this study, we evaluated how biocrusts affect the functional diversity and biomass of microbial diversities beneath biocrusts. Methods We performed two microcosm experiments using biocrust-forming lichens where we manipulated their biotic attributes to test independently the effects of species richness (from two to eight species), composition, evenness (maximal and low evenness) and spatial pattern (clumped and random distribution) on the microbial catabolic profile and microbial functional diversity. Results Microcosms with a random pattern had a higher microbial catabolic profile than those with a clumped pattern. Significant richness × evenness × pattern and richness × evenness interactions were found when analyzing microbial catabolic profile and biomass, respectively. Microcosms with a random pattern, intermediate number of species, and maximal evenness level had higher microbial catabolic profile. At the maximal evenness level, assemblages had higher microbial catabolic profile and microbial biomass when they contained four species. The richness × evenness × pattern interaction was the most informative predictor of variations in microbial catabolic profile. Conclusions Our results indicate that soil microorganisms are influenced by biocrusts, just as they are influenced by plants, and highlight the importance of higher order interactions among species richness, evenness, and spatial pattern as drivers of microbial communities. The results also emphasize the importance of studying several biotic attributes simultaneously when studying biocrust-soil microorganism interactions, as in nature, community properties do not exert their influence in isolation.

Description: Background and aims Heterotrophic growth relies on remobilisation of seed reserves and mineral absorption. We used a compartmental model to investigate the fluxes of N absorption and remobilisation of N reserves in a legume seed with high protein content. Methods Seedling growth was studied during the heterotrophic stage in two genotypes of Medicago truncatula as a function of N supply. N absorption and seed remobilisation fluxes were distinguished in a 15  N labelling experiment. Results Remobilisation of seed N reserves was high during germination, but N uptake started as soon as the radicle protruded. Both sources contributed to high elongation rates of the radicle and hypocotyl. When organ lengths stabilised, there was an efflux of N from the cotyledons and roots indicating that seedling growth was limited by carbohydrate production. No significant differences between genotypes were observed except for early N uptake, which was lower in the genotype with the highest initial seed N content. Conclusions N fluxes were similar to those of other non-legume dicotyledonous species but differed from monocotyledonous species. These results improve our understanding of the effects of mineral fertilisation on crop establishment. The compartmental model is a useful tool to analyse N fluxes patterns within and between diverse species, in relation to seed characteristics and soil N availability.

Description: Aims Grazing exclusion practices can be promising restoration techniques where ecosystem degradation follows from rapidly increasing grazing pressure, as widely observed in northern Chinese grasslands. However, the mechanisms of plant-soil interactions responsible for nutrient cycling restoration remain unclear. Methods We examined the functional response of the two most dominant grass species with contrasting nutrient economies to a grazing exclusion chronosequence varying greatly in soil moisture and extractable N and P. Results The relative biomass of the nutrient acquisitive species Leymus chinensis increased while that of the nutrient conservative Stipa grandis decreased across the chronosequence. Leymus chinensis displayed increasing leaf nutrient concentration and decreasing nutrient resorption with time since grazing exclusion for both N and P. In contrast, S. grandis showed decreasing leaf N and P concentrations and largely stable nutrient resorption. Conclusions These differences in plasticity, with respect to nutrient stoichiometry and resorption, suggest contrasting abilities of these two dominant species to compete for soil resources and/or differences in their affinity to the changing forms of soil available N and P likely occurring along the restoration gradient. Ecosystem trajectory of change after grazing exclusion appears therefore largely dependent on the nutrient use strategies of co-occurring dominant grassland species.

Description: Background and aims Policy-oriented successive land use conversion intensively occurred in seasonally frozen zones of China during the past five decades. However, responses of soil carbon (C) and nitrogen (N) to land use conversion under cold temperate climates are not fully understood. The objective was to characterize C and N variations following a succession of forest, dryland and paddy. Methods Soil cores were collected for 6 layers with a 10 cm increment from three adjacent chronosequences to determine concentrations of soil organic carbon (SOC), total nitrogen (TN), dissolved organic carbon (DOC) and alkaline hydrolysable nitrogen (HN). Analysis of variance with multivariate general linear model was operated on data sets. Results Significant losses of SOC and TN storages subject to land use conversion were merely confined within 0 – 10 cm layer, decreasing by 16 % and 38 % for forest to dryland and by 23 % and 43 % for forest to paddy, respectively. Cultivation also influenced SOC and TN stocks at 20 – 40 cm depth for dryland and 20 – 60 cm depth for paddy with increases by 38 Mg C ha −1 and 2.8 Mg N ha −1 for forest to dryland, and by 56 Mg C ha −1 and 4.1 Mg N ha −1 for forest to paddy, respectively. Conclusion Successive land use conversion from forest to cropland affected C and N levels in deeper layers, demonstrating the high potentials of subsoil in sequestrating C and N. The extents of cultivation-induced SOC and TN redistribution along soil profile varied among different agricultural systems. DOC and HN changes interpreted SOC and TN changes with land use, presenting high involvements of soluble compartments in SOC and TN variations. The net variation in SOC/TN ratio effectively indicated C and N changes when dryland was converted to paddy.

Description: Background and aims Salinization of soils causes severe problems to plant growth. With the important role of stoichiometry in many ecological processes, this study investigated the effect of an asexual Epichloë endophyte on the nutrient stoichiometry of wild barley ( Hordeum brevisubulatum ) under salt stress. Methods Plants with (E+) and without endophyte (E−) were subjected to different NaCl treatments (0, 150, 300, 450 and 600 mM). After 15 days, the dry weight as well as the carbon (C), nitrogen (N), phosphorus (P), sodium (Na + ) and potassium (K + ) contents in the plants were determined. Results Salt stress significantly reduced the growth and nutrient absorption of wild barley. The biomass as well as the N, P and K + contents were higher while the Na + content was lower in E+ plants than in E− plants. However, there was no significant effect on C content between E+ and E− plants. The findings also showed that E+ plants had lower ratios of C:N, C:P, Na + :K + and a higher ratio of N:P than E− plants. Conclusions The Epichloë endophyte played an important role in maintaining the growth of the host plants by promoting nutrient absorption and adjusting the ionic balance. The results have enhanced knowledge of the application of endophytes that will enable better crop production and ecological conservation.

Description: Aims The root-to-shoot transport of manganese (Mn) exhibited intra-specific characters in different grape genotypes. The majority of Mn was stored in the roots of the grape cultivar Jinshou, while it was mainly transferred to the shoots in the cultivar Combier. The aims of the present study was to reveal the complex interplay of gene expression endowing grape a high tolerance to excess Mn and to explore the relation of the expression of Mn transporters with the contrast root-to-shoot translocation pattern of excess Mn in different grape cultivars. Methods The root transcriptome changes in both cultivars were analyzed by high-throughput sequencing and validated by quantitative RT-PCR. Results and conclusion Compared to Jinshou, Combier exhibited a markedly high transcripts level in the Mn transporter unigenes in the roots independent of the Mn treatment, accompanied by a higher expression level of genes encoding nicotianamine synthase, heavy metal-transporting ATPase, ZIP family member and IRT1-like proteins, which could facilitate Mn transport from the roots to the shoots in Combier. However, the expression level of genes involved in the subcellular vesicular transport pathway was much higher in Jinshou than in Combier, with a higher transcripts level of V-ATPase, vacuolar protein and the proteins for the synthesis of organic acid, such as the citrate cycle and glycolysis pathway. All of these changes allowed Mn to be easily chelated and compartmented to root cortical and epidermic cell vacuoles in Jinshou, accompanied with higher transcription and activity levels of stress-related enzymes, endowing Jinshou a high degree of tolerance to excess Mn. The grape transcriptome responses to Mn stress were also discussed.

Description: Aims This study aimed at disentangling the respective influence of species, environment, root size and root type in tree root architecture. Method The root system of 106 adult trees from ten species was carefully extracted from French dikes. Root length and proximal diameter, length and diameter of root segments and branch insertion diameter were measured. Root branching and tapering rates, segment taper, classical (P) and new architectural parameters related to branching patterns were computed. Results Two contrasting root types called “running” (R) and “short” (S), were identified from growth and architectural parameters. Compared to S roots, R roots were longer for an equivalent proximal diameter and singled out with lower tapering rate, branching rate and segment taper and with smaller branches. Their main axis lost less in diameter at branching point for branches of the same size. Tree species had little influence on these architectural parameters. The effect of soil material (coarse vs fine) was significant mainly on root size, on branching rate in fine material, and only secondarily on some branching patterns for running roots and on segment taper. The new architectural parameters describe branching patterns more accurately than classical ones. Conclusion This study provides an original insight in tree root architectural analysis, proposing a new root typology and innovative parameters for the description and modeling of root architecture.

Description: Background and aims Numerous microorganisms have been isolated from trinitrotoluene (TNT)-contaminated soils, however TNT tends to persist, indicating that the microbial biomass or activity is insufficient for degradation. Deep-rooting trees at military sites have been found to take-up contaminants from groundwater, and the extensive root and endosphere provide ideal niches for microbial TNT-transformations. Methods We characterised the rhizosphere, root endosphere and endo-phyllosphere bacteria of Acer pseudoplatanus growing at a historically TNT-contaminated location, using 16S rRNA gene fingerprinting, bacteria isolation, oxidoreductase gene-cloning, in planta growth-promotion (PGP) tests, inoculation, plant physiology measurements and microscopy. Results Based on terminal-restriction-fragment-length-polymorphism analysis, bulk soil and rhizosphere samples were highly clustered. Proteo- and Actinobacteria dominated the rhizosphere and root endosphere, whereas Alphaproteobacteria were more abundant in shoots and Actinobacteria in leaves. We isolated multiple PGP-bacteria and cloned 5 flavin-oxidoreductases belonging to the Old Yellow Enzyme family involved in TNT-reduction from 3 Pseudomonas spp., the leaf symbiont Stenotrophomonas chelatiphaga and the root endophyte Variovorax ginsengisola . Conclusions The inoculation with a selection of these strains, consortium CAP9, which combines efficient TNT-transformation capabilities with beneficial PGP-properties, has the ability to detoxify TNT in the bent grass ( Agrostis capillaris ) rhizosphere, stimulate plant growth and improve plant health under TNT stress.

Description: Aims The objective of this study was to investigate phosphine-induced changes in enzyme activities (acid phosphatase (ACP), urease, invertase, dehydrogenase) and effects of phosphine on available phosphorus in rhizospheric and non-rhizospheric soils. Methods Rice seedlings, as model plant, were exposed to different ambient concentrations of phosphine (0, 1.4, 4.2 and 7.0 mg m −3 ) for a period of 30 days, and the enzyme activities and available phosphorus in both rhizospheric and non-rhizospheric soils were monitored for different phosphine concentrations and exposure times. Results In the first 2 weeks in the rhizospheric soil, the activities of urease, invertase and dehydrogenase increased slowly with phosphine exposure time in both rhizospheric and non-rhizospheric soils, although ACP activity displayed a slight drop in the rhizosphere; however, the activities of all these enzymes dramatically increased with phosphine concentration and exposure time after 15 days. Enzyme activities in rhizosphere soil are generally greater than those in non-rhizosphere soil, exhibiting effects of the rhizosphere. Increase in phosphine exposure concentrations also increased the available phosphorus in rhizosphere and non-rhizosphere soils. Conclusions Phosphine exposure increases soil enzyme activities and available phosphorus in both rhizosphere and non-rhizosphere which is beneficial for rice growth.

Description: Background and aims A fast and reliable phenotyping system forms a major bottleneck in root exudation research. Our goal was to develop such a system to quantify genetic and environmental effects on root exudation. Another aim was characterizing non-sterile phenotyping. Methods We developed a system in which plants can be grown with non-sterile shoot environments and sterile rhizospheres. These sterile systems were compared with non-sterile controls. Results In non-sterile rhizospheres exogenous carbon disappeared quickly with a half-life of 2 to 3 h and root exudate concentrations remained below detection limit. In sterile rhizospheres exogenous carbon levels were relatively stable or depleted slower than in non-sterile rhizospheres and organic acid build-up occurred. Tomato ( Solanum lycopersicum ) could be grown with sterile roots for several months. Conclusions The differences in carbon depletion in sterile and non-sterile rhizospheres was most likely due to the absence of microbial catabolism in sterile rhizospheres. These results prove that using a sterile phenotyping system is essential to study the quantity and composition of root exudates. The sterile system described in this paper eliminates the obscuring effect caused by microbes on exudation levels. It offers a stable, reliable and easy phenotyping method and can be used to investigate genetic and environmental effects on exudation.

Description: Backgrouand and aim Myxospermous seeds become bound by mucilage upon hydration and this trait is ecologically important. Major impacts could be enhancing seed-soil contact and improving water retention, which we quantify in this study. Methods Myxospermous or demucilaged seeds of Capsella bursa - pastoris L. Medik. (shepherd’s purse) were added to a test sandy clay loam at seed : soil densities of 5 and 10 % [w/w]. The soil water retention and hydraulic conductivity were assessed. Soil rheology was also assessed using extracted mucilage only amendment at 0.5 and 1 % [w/w]. Results Shepherd’s purse seeds increased soil water retention and reduced soil hydraulic conductivity for myxospermous and demucilaged seeds. Soil rheological properties (complex shear modulus, viscosity and yield stress) increased in response to seed mucilage addition, and became more pronounced as soil dried. The mucilage had greatest impact on the yield stress compared to the other rheology parameters. Conclusions The densities of myxospermous and non-myxospermous seeds, and mucilage tested here reflect that may be found naturally in soil seedbanks. The findings provide the first evidence that the soil seedbank provided from a wild arable species may regulate the soil water retention and enhance soil stability, and that this capacity is greater for myxospermous seeds.

Description: Aims This study aimed to determine the influence of tree species on soil microbial community structure. Methods We conducted a litter and root manipulation and a short-term nitrogen (N) addition experiment in 19-year-old broadleaf Mytilaria laosensis (Hamamelidaceae) and coniferous Chinese fir ( Cunninghamia lanceolata ) plantations in subtropical China. Phospholipid fatty acid (PLFA) analysis was used to examine treatment effects on soil microbial community structure. Redundancy analysis (RDA) was performed to determine the relationships between individual PLFAs and soil properties (soil pH, carbon (C) and N concentration and C:N ratio). Results Soil C:N ratio was significantly greater in M. laosensis (17.9) than in C. lanceolata (16.2). Soil C:N ratio was the key factor affecting the soil microbial community regardless of tree species and the litter, root and N treatments at our study site. The fungal biomarkers, 18:1ω9 and 18:2ω6,9 were significantly and positively related to soil C:N ratio and the abundance of bacterial lipid biomarkers was negatively related to soil C:N ratio. N addition for 8 months did not change the biomass and structure of the microbial community in M. laosensis and C. lanceolata soils. Soil nutrient availability before N addition was an important factor in determining the effect of N fertilization on soil microbial biomass and activity. PLFA analysis showed that root exclusion significantly decreased the abundance of the fungal biomarkers and increased the abundance of the Gram-positive bacteria. Rootless plots had a relatively lower Gram-positive to Gram-negative bacteria ratio and a higher fungi to bacteria ratio compared to the plots with roots under both M. laosensis and C. lanceolata . The response of arbuscular mycorrhizal fungi (16:1ω5) to root exclusion was species-specific. Conclusions These observations suggest that soil C:N ratio was an important factor in influencing soil microbial community structure. Further studies are required to confirm the long-term effect of tree species on soil microbial community structure.

Description: Soils host highly diverse organism communities organized in complex food webs that strongly contribute to biological soil functions. However, it is a problem to evaluate these contributions because there are only few methods available which directly address soil functioning and ecosystem services. In fact, there are just two functional methods, which are useful for assessing quantitavely the activity of soil organisms, especially invertebrates. Both are related to organic matter decomposition (and thus nutrient cycling): the litter-bag-test in which mass loss of organic material is measured, but takes a long time, and the bait-lamina test, which is used to measure soil invertebrates’ feeding activity and its vertical distribution in situ. Both methods are internationally standardized. Currently, the use of the bait-lamina test seems to increase, mainly because it has been recommended for regulatory applications. The experiences with the bait-lamina test as described in the literature including the paper of Musso et al. ( 2014 ) are a good basis for improvements to be recommended, such as performing a preliminary test for the identification of the most appropriate study duration, using a standard bait material (i.e. to facilitate the comparison of data sets from different studies), and optimizing the “classic” study design in order to increase the statistical power of the test.

Description: Aim Fusarium wilt (Panama disease) caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) is a soilborne disease that severely devastates the banana industry worldwide. We aimed to isolate beneficial endophytic bacterial strains against Panama disease. Methods From different plant species, including reeds ( Phragmites australis ), vetiver grass ( Chrysopogon zizanioides ), and banana plants (Cavendish cv. Pei-Chiao, Cavendish cv. Formosana, and Musa sapientum cv. Rose), endophytes were screened and characterized. The diversity and community of endophytes within banana plants were analyzed by PCR-denaturing gradient gel electrophoresis (DGGE). The banana tissue culture plantlets were inoculated with the candidate endophyte, Burkholderia cenocepacia 869T2, and effects of in planta biocontrol were observed. Results Endophytic B. cenocepacia 869T2 decreased the disease incidence of Fusarium wilt on treated banana plants to 3.4 %, comparing to 24.5 % of non-inoculated plants infected in the field test within a 7-month period. Furthermore, significant growth promoting of 869T2 inoculated banana plants was observed in field experiments. Conclusions In addition to 869T2 genomic sequence data, our results suggest that the pyrrolnitrin and pyrroloquinoline quinone potential producer, B. cenocepacia 869T2, is a good biological control agent (BCA) for use in the biocontrol of Fusarium wilt and plant promotion.

Description: Background and aims Chickpea rhizobia did not occur naturally in Australian cropping soils, necessitating inoculation at sowing. Now, after more than 30 years of chickpea cultivation using a single inoculant strain, CC1192, it is likely that chickpea rhizobia are established in 1.0–1.5 Mha cropping land. The aims of this study were to examine effects of the naturalised chickpea rhizobia on nodulation and productivity (total crop N, crop N fixed and grain yield) of commercial chickpea. Methods Soil was sampled from 26 fields to estimate chickpea rhizobial numbers, relate numbers to edaphic factors and years since previous chickpea crop, determine the proportions of CC1192 and novel strains using RAPD-PCR and subject a subset of novel strains from one site to 16S rRNA analysis. Nodules were harvested from 15 inoculated, commercial chickpea crops to determine occupancy by CC1192. The symbiotic effectiveness of a second subset of novel strains was assessed. Results The mean number of rhizobia in the soils varied from log 0.08 to log 5.16 rhizobia g soil −1 with population size positively correlated with soil moisture content and negatively correlated with salt concentration (EC e ). RAPD-PCR analysis of 570 strains of chickpea rhizobia isolated from the soils indicated only 14 % with molecular fingerprints similar to CC1192. Occupancy by CC1192 of nodules harvested from commercial crops ranged 0–100 %, with an average of 53 %. Occupancy by CC1192 declined by an average 17 % with each log unit increase in numbers of novel chickpea rhizobia. Conclusions We found no evidence that the novel mesorhizobia in the chickpea soils compromised N 2 fixation or productivity of commercial chickpea crops, even though individual strains had generally reduced symbiotic effectiveness relative to CC1192.

Description: Objectives Carbon (C) content in pools of very young soils that developed during 45 years from loess was analysed in relation to vegetation: deciduous and coniferous forests and cropland. We hypothesised that variations in the amount of particulate organic matter (POM) can explain the C accumulation and also affects the C bound to mineral surfaces in soil under various vegetation. Methods Soil samples were collected under three vegetation types of a 45-year-old experiment focused on initial soil development. Aggregate and density fractionations were combined to analyse C accumulation in large and small macro- and microaggregates as well as in free and occluded POM and mineral factions. Results Deciduous forest soil accumulated the highest C content in the 0–5 cm layer (43 g C kg −1 ), whereas values in coniferous forest and arable soils were lower (30 and 12 g C kg −1 , respectively). The highest portion of C in arable soil was accumulated in the mineral fraction (80 %), whereas 50–60 % of the C in forest soils were in POM. More C was associated with minerals in deciduous forest soil (16 g C kg −1 soil) than under coniferous forest and arable land (8–10 g C kg −1 soil). Conclusions Particulate organic matter explains most of the differences in organic C accumulation in soils developed during 45 years under the three vegetation types on identical parent material. The C content of the mineral soil fraction was controlled by plant cover and contributed the most to differences in C accumulation in soils developed under similar vegetation type (forest).

Description: Background Phospholipid fatty acid (PLFA) analysis is an effective non-culture-based technique for providing information on the living soil microbial community. The coupling of 13 C tracers with PLFA analysis can indicate the response of microbial populations to environmental change and has been widely used to trace C flux in soil-plant systems. Scope Based on studies applying 13 C PLFA analysis, the current technological status, current applications and future opportunities are discussed and evaluated. First we describe some aspects of the labelling and analytical methodology. The approaches to study the incorporation of 13 C substrate and rhizodeposition C into soil microbial communities are compared. We continue with the application of 13 C-labelling to study soil microbial communities, including the utilization of soil mineralisation products, the C flux from plants into the soil microbial pool, the biodegradation of pollutants and on the application to a specific microbial group, i.e. methanotrophs. Additionally, some perspectives on the limitations of the 13 C PLFA method and future research avenues are noted. Conclusions Although including some limitations and complications, the 13 C PLFA method provides an excellent tool for understanding the relationship between microbial populations and soil biogeochemical cycling, thus providing a key to open the soil microbial black box.

Description: Background and aims Arbuscular mycorrhizas (AM) enhance plant uptake of a range of mineral nutrients from the soil. Interactions between nutrients in the soil and plant, are complex, and can be affected by AM. Using a mycorrhiza-defective mutant tomato genotype ( rmc ) and its wild-type (76R), provides a novel method to study AM functioning. Methods We present a meta-analysis comparing tissue nutrient concentration (P, Zn, K, Ca, Cu, Mg, Mn, S, B, Na, Fe), biomass and mycorrhizal colonisation data between the 76R and rmc genotypes, across a number of studies that have used this pair of tomato genotypes. Particular attention is paid to interactions between soil P or soil Zn, with tissue nutrients. Results For most nutrients, the difference in concentration between genotypes was significantly affected either by soil P, soil Zn, or both. When soil P was deficient, AM were particularly beneficial in terms of uptake of not only P, but other nutrients as well. Conclusions Colonisation by AMF significantly affects the uptake of many soil macro- and micro-nutrients. Furthermore, the soil P and Zn status also influences the difference in nutrient concentrations between mycorrhizal and non-mycorrhizal plants. The interactions identified by this meta-analysis provide a basis for future research in this area.

Description: Aims To examine heavy metal-induced regulatory mechanisms at the transcriptional level, a cell wall-associated receptor kinase ( WAK ) gene, OsWAK11 and its upstream promoter region (−946/+28) were isolated from Oryza sativa. OsWAK11 expression in response to abiotic stress was examined using a β-glucuronidase (GUS) gene fusion. Methods Semi-quantitative RT-PCR was used to analyze expression of the OsWAK11 gene. Histochemical detection of GUS was conducted by X-gluc staining methods, and fluorometric measurements of GUS activity were made with 4-methyl umbelliferyl glucuronide (MUG) substrate. Results The WAK promoter (−946/+28) responded to aluminum chloride, sodium chloride, and copper (II) sulfate with 3.0-, 2.2-, or 6.4-fold induction of GUS activity, respectively. Sodium nitroprusside and wounding treatment stimulated GUS activity. A histochemical analysis revealed strong GUS staining in the hypocotyls, cotyledons, first leaf, and petiole of cotyledons in transgenic tobacco seedlings. Strong GUS staining was also observed in the stigma and ovary of mature flowers, but not in the stamens. Conclusion OsWAK11 expression is regulated by aluminum, sodium, and copper. The GUS expression observed in transgenic tobacco carrying WAK11 promoter demonstrated significant tissue-specificity. The OsWAK11 promoter was strongly upregulated in response to metals and wounding.

Description: Aims Biochar (BC) and humic acid product (HAP) soil amendments may improve plant performance under water-limited conditions. Our aim was to investigate if BC and HAP amendments, alone or in combination, will have positive and synergistic effects. Methods A three-factorial fully randomized study was carried out in the greenhouse for 66 days, including the factors ‘BC’, ‘HAP’ and ‘water regime’. Maize ( Zea mays var. ‘Amadeo’ DKC-3399) was grown in pots (6 kg sandy soil pot −1 ) amended with/without BC (0, 1.5 and 3 %; w/w ) and with/without HAP (0 or an equivalent of 8 kg ha −1 ). Two water regimes, limited and frequent (H 2 O limit , H 2 O frequ ), were applied after day 28 following seedling establishment at 60 % water holding capacity (WHC). In the H 2 O limit treatment, the soil water content was allowed to drop until wilting symptoms became visible (25–30 % WHC) while in H 2 O frequ the WHC was brought to 60 % of the maximum on a daily basis Results BC but not HAP, added alone or in combination with BC, significantly increased the biomass yield and the water and N use efficiency of plants at both water regimes. The BC-mediated relative increase in the yield was equal with both watering regimes, refuting initial hypotheses. BC had generally a stimulating effect on water relations and photosynthesis, it increased the relative water content and the leaf osmotic potential, decreased the stomatal resistance and stimulated the leaf gas exchange (transpiration). Both, BC and pure HAP addition, stimulated photosynthesis by increasing the electron transport rate (ETR) of photosystem II (PSII) and of the ratio between effective photochemical quantum yield to non-photochemical quenching (Y(II)/Y(NPQ), revealing reduced heat dissipation. Conclusions Biochar use in poor sandy soils can improve plant growth by improving soil-plant water relations and photosynthesis under both H 2 O frequ and H 2 O limit conditions. HAP loading, however, did not improve the effect of biochar or vice versa.

Description: Aims Herbaspirillum spp. has been described as bacteria that colonizes not only maize roots but also stems and leaves. This study aimed to access the growth-promoting effect of 21 strains of Herbaspirillum on maize plants. This study is composed by 12 strains of the H. seropedicae , 5 strains of the H. rubrisubalbicans and 4 strains of the H. frisingense. Methods Bacterial selection was performed in two phases, consisting on planting the BRS4157 maize variety and hybrid SHS5050 in the greenhouse, with sterile and non-sterile substrate and in the field. After 40 days, the greenhouse plants were harvested and the dry matter accumulation of the aerial part and roots were measured. The best-performing strain was tested in field trials treated with 40 and 80 kg ha −1 of N fertilizer, parallel to the same treatments without inoculation. In this trial, the grain yield was evaluated as well as the contribution of biological nitrogen fixation (BNF), using the technique of natural abundance of 15  N. Results The results showed that H. seropedicae ZAE94 was the best strain under controlled conditions and its application as a field inoculant increased maize yield up to 34 %, depending on the plant genotype. The BNF quantification revealed that 37 % BNF-derived plant nitrogen in the hybrid SHS5050 inoculated with the H. seropedicae strain ZAE94. Conclusions The difference in response to nitrogen as well as to inoculation depends on the selected plant genotype and the bacterial inoculant. H. seropedicae ZAE94 can promote plant growth and contribute biologically with fixed nitrogen in the maize hybrid SHS5050.

Description: Aims Induction of lignin biosynthesis is an adaptive response of plants subjected to many abiotic stresses. In this study, we examined the response of lignin biosynthesis to copper (Cu) stress, with a particular focus on the regulatory mechanism. Methods We performed a transcriptomic analysis of rice ( Oryza sativa L.) roots, and the microarray data on lignin biosynthesis pathway genes were corroborated by quantitative reverse transcription–polymerase chain reaction (qRT-PCR) analysis. Physiological analyses of rice seedlings treated with Cu(II) sulfate (CuSO 4 ) were used to confirm the relationship between excess Cu and lignin biosynthesis. In addition, we examined the role of hydrogen peroxide (H 2 O 2 ) in Cu-induced lignin biosynthesis through pretreatments with an NADPH oxidase inhibitor (diphenyleneiodonium, DPI) and a H 2 O 2 scavenger (dimethylthiourea, DMTU). Results Lignin biosynthesis pathway genes were upregulated under Cu stress. The lignin content of rice roots increased significantly with increasing concentrations and durations of Cu treatment; elevations in root lignin content were correlated with marked inhibitions in root growth. Pretreatments with DPI and DMTU inhibited the activities of Cu-induced lignin polymerization enzymes (peroxidase, POD and laccase, LAC) and lignin accumulation in rice roots. Conversely, exogenous H 2 O 2 increased the root lignin content. Conclusions Rice roots under Cu stress accumulate lignin through enhanced polymerization of lignin monolignol, a mechanism that requires Cu stress induced H 2 O 2 .

Description: Aims Our objective was to assess the impacts of water table position and plant functional type on peat structure, plant community composition and aboveground plant production. Methods We initiated a full factorial experiment with 2 water table (WT) treatments (high and low) and 3 plant functional groups (PFG: sedge, Ericaceae, sedge and Ericaceae- unmanipulated) in twenty-four 1 m 3 intact peatland mesocosms. We measured vegetation cover, aboveground plant production, and peat subsidence to analyze interactive PFG and WT effects. Results Sphagnum rubellum cover increased under high WT, while Polytrichum cover increased with low WT and in sedge only PFGs. Sphagnum production was greatest with high WT, while vascular plant production was greater in low WT treatments. There was an interactive WT x PFG effect on Ericaceae production. Lowered WT resulted in significant peat surface change and increased subsidence. There were significant PFG and WT effects on net peat accumulation, with the lowest rates of accumulation, high and low WT, in sedge only PFGs. Conclusions The shift in water balance leading to lowered water table position predicted with changing climate could impact plant community composition and production, and would likely result in the subsidence of peat.

Description: Background and aims Temperate rice paddy fields are generally flooded for less than 100 days a year during the rice cropping season and are kept under dried soil conditions during the fallow season of over 200 days. The impacts of rice paddy soil on the global warming potential (GWP) are generally analysed during rice cultivation, without consideration of the fallow season, using only methane (CH 4 ) and nitrous oxide (N 2 O) fluxes. To compare the impact of greenhouse gas (GHG) emissions during the flooded rice cultivation and the dried fallow seasons on the annual GWP in a mono-rice cultivation system, the emission fluxes of CH 4 , N 2 O and carbon dioxide (CO 2 ) were evaluated under two different fertilization systems (NPK and NPK + Cover crop) for two consecutive years. Methods In the NPK + Cover crop treatment, a mixture of barley and hairy vetch were cultivated as a winter cover crop without fertilization during the fallow season. The total above-ground biomass (36 Mg fresh weight ha −1 , moisture content 68.9 %, C/N ratio 20.6) was incorporated as a green manure one week before rice transplanting. The same levels of chemical fertilisers were applied for rice cultivation in the NPK and NPK + Cover crop treatments. The emission rates of CH 4 , CO 2 , and N 2 O gases were simultaneously monitored once a week using the closed-chamber method. However, because the CO 2 fluxes included only soil respiration and excluded soil C sequestration through cover cropping and its recycling of biomass, the net ecosystem C budget (NECB), which is defined as the difference between total organic C input and output, was estimated to ascertain pure CO 2 emission fluxes. Finally, the net global warming potential (GWP), which was calculated as CO 2 equivalents by multiplying the seasonal CH 4 , CO 2 , and N 2 O fluxes by 25, 1, and 298, respectively, was compared between the two treatments and the two seasons. Results In the NPK treatment, the annual net GWP value was 10.7–11.7 Mg CO 2 eq. ha −1 , in which approximately 56–62 % was affected by the seasonal net GWP value during the fallow season. Cover crop cultivation during the fallow season and its biomass addition as a green manure for rice cultivation significantly increased the total net GWP value to 28.2–31.5 Mg ha −1 , in which approximately 73–76 % was weighted by the seasonal net GWP value during rice cultivation. Carbon dioxide was the most influential GHG on increasing the growth scale of total net GWP during the dried fallow season, but CH 4 most strongly influenced the annual net GWP scale during the rice cropping season, irrespective of soil management conditions. The contribution of CH 4 to the annual net GWP value significantly increased as a result of cover crops biomass addition from 34–39 % in the NPK treatment to 88–91 % in the NPK + Cover crop treatment. Conclusion The dried fallow season contributed to approximately 30–60 % of the annual net GWP scale through GHG emissions. Therefore, proper soil management strategies should be developed to decrease GHG emissions during the fallow season in mono-rice paddy fields.

Description: Background and aims Degradation of physical, chemical and biological properties of soils in sub-Saharan Africa mainly results from little or no organic resource application coupled with sub-optimal fertilizer application. A study was conducted over three seasons, from March 2010 to August 2011, to evaluate potential of six organic materials (bagasse, cow manure, filtermud, maize stover, sugarcane straw and Tithonia diversifolia ) for compost production and their influence on maize yield and soil fauna diversity. Methods Treatments comprised of the six composts, commercial fertilizer and no-input control, laid out in randomized complete block design in four replicates. Soil macrofauna were collected using soil monolith method. Data obtained were subjected to analysis of variance (ANOVA) using GENSTAT whereas differences were evaluated using Fisher’s least significant difference (LSD). Correlation between macrofauna and soil chemical properties was done using CANOCO 3.1. Results The ANOVA showed significantly higher N and P on filtermud (10.0 g N kg −1 and 979 mg P kg −1 ) and T. diversifolia (9.6 g N kg −1 and 614 mg P kg −1 ) composts. Generally, amending soils with composts increased C, N and P of the soil by 90 %, 29 % and 20 %, respectively, while fertilizer treated plots recorded 42 %, 4 % and 110 % increase in C, N and P, respectively. Control plots recorded 25 % increase in C, but 15 % and 50 % decline in N and P, respectively. Maize yields were highest in fertilizer (4.4 Mg ha −1 ), followed by composts (2.8 Mg ha −1 ) and lowest in control plots (1.4 Mg ha −1 ). Soil macrofauna responded positively to addition of composts. Isopterans, Oligochaeta and Hymenopterans dominated the sites constituting 44 %, 26 % and 17 %, respectively of all the macrofauna. Relationships between macrofauna and soil chemical properties were positively significant. Conclusions Results of this study demonstrate the potential of composts in improving soil biodiversity and crop productivity.

Description: Background and aims The aim of this study was to explore the diversity of arbuscular mycorrhizal (AM) fungi in agroecosystems of the Canadian Prairies and determine whether soil type and land use impact the diversity and composition of these important communities. Methods We used two separate field surveys and methods to address these questions. The first survey involved collecting soil samples from five different soil types and spores were morphologically identified from trap cultures established using these soil samples. The second survey involved collecting soil samples from two different land use types across the four major Chernozem great groups to characterize the AM fungal communities using 454 GS FLX pyrosequencing of the small subunit rDNA region. Results The first survey found that Vertisolic soil had a significantly higher AM spore richness compared to the Chernozem soils. Both surveys revealed no effect of soil type on the diversity and composition of AM fungal communities among the Chernozem great groups. The two different methods used in this study revealed differences in the proportional representation of certain AM fungal taxa. Land use had a strong impact on the AM fungal communities in the Canadian Prairies as roadsides harboured a more diverse and compositionally different communities compared to annually cropped fields. Conclusions Overall, soil type appears to have little to no effect on AM fungal communities among the Chernozem great groups in the Canadian Prairies, and land use practices impact the diversity and composition of these communities.

Description: Aims Plants with precise root foraging patterns can proliferate roots preferentially in nutrient-rich soil patches. When nutrients are distributed heterogeneously, this trait is often competitively advantageous in pot experiments but not field experiments. We hypothesized that this difference is due to belowground herbivory under field conditions. Methods We performed pot experiments using seedlings of Lolium perenne (a more precise root foraging species) and Plantago lanceolata (a less precise root foraging species). The experiment had a two-way factorial randomized block design, with nutrient distribution pattern (homogeneous or heterogeneous) and belowground herbivore (present or absent) as the two factors. Each pot contained one seedling of each species. Results With no herbivore present, plant biomass was smaller in the heterogeneous nutrient treatment than in the homogeneous treatment in P. lanceolata , but not in L. perenne . Under homogeneous nutrient distribution, plant biomass was lower in both species with a herbivore present than with no herbivore. Under heterogeneous nutrient distribution, biomass reduction due to herbivory occurred only in L. perenne . Conclusions Roots of the precise root foraging species were grazed more under the heterogeneous nutrient distribution, suggesting that the herbivore more efficiently foraged for roots in nutrient-rich soil patches.

Description: Aims The mechanisms underlying magnesium (Mg) uptake by plant roots remain to be fully elucidated. In particular, there is little information about the effects of Mg deficiency on Mg uptake activity. A Mg uptake kinetic study is essential for better understanding the Mg uptake system. Methods We performed a Mg uptake tracer experiment in rice plants using 28  Mg. Results Mg uptake was mediated by high- and low-affinity transport systems. The K m value of the high-affinity transport system was approximately 70 μM under Mg-deficient conditions. The Mg uptake activity was promoted by Mg deficiency, which in turn fell to the basal level after 5- min of Mg resupply. The induced uptake rate was inhibited by ionophore treatment, suggesting that an energy-dependent uptake system is enhanced by Mg deficiency. Conclusions The Mg uptake changes rapidly with Mg conditions in rice, as revealed by a 28  Mg tracer experiment. This technique is expected to be applicable for Mg uptake analyses, particularly in mutants or other lines.

Description: Background and aim Nitrogen-fixing bacteria or diazotrophs have been isolated for many years using different formulations of N-free semi-solid media. However, the strategies used to isolate them, and the recipes of these media, are scattered through the published literature and in other sources that are more difficult to access and which are not always retrievable. Therefore, the aim of this work was to collate the various methods and recipes, and to provide a comprehensive methodological guide and their use by the scientific community working in the field of biological nitrogen fixation (BNF), particularly with non-leguminous plants. Methods Procedures used for bacterial counting and identification either from rhizosphere soil or on the surface of, or within, plant tissues (to access “endophytic” bacteria) are presented in detail, including colony and cell morphologies. More importantly, appropriate recipes available for each N-free semi-solid culture medium that are used to count and isolate various diazotrophs are presented. Results It is recognized by those working in the field of BNF with non-legumes that the development of the N-free semi-solid medium has allowed a tremendous accumulation of knowledge on the ecology and physiology of their associated diazotrophs. At least 20 nitrogen-fixing species have been isolated and identified based on the enrichment method originally developed by Döbereiner, Day and collaborators in the 70’s. In spite of all the advances in molecular techniques used to detect bacteria, in most cases the initial isolation and identification of these diazotrophs still requires semi-solid media. Conclusions The introduction of the N-free semi-solid medium opened new opportunities for those working in the area of BNF with non-legumes not only for elucidating the important role played by their associated microorganisms, but also because some of these bacteria that were isolated using semi-solid media are now being recommended as plant growth-promoting inoculants for sugarcane ( Saccharum sp.), maize ( Zea mays ) and wheat ( Triticum aestivum ) in Brazil and other countries. Further progress in the field could be made by using a combination of culture-independent molecular community analyses, in situ activity assessments with probe-directed enrichment, and isolation of target strains using modified or standard semi-solid media.

Description: Background and aims Whereas the expression patterns and kinetic properties of the rice ( Oryza sativa ) phosphate transporter gene OsPht1; 6 ( OsPT6 ) are well documented, little is known about the biological functions of this gene. The aim of this study was to investigate the roles of OsPT6 in inorganic phosphate (Pi) acquisition and mobilization, and examine its potential to enhance agricultural production. Methods Here, we generated OsPT6 overexpression transgenic plants using Wuyujing 7, a widely cultivated variety of japonica rice, and then treated transgenic lines and wild type with different Pi supply in hydroponic and soil experiments to explore the functions of OsPT6 in rice. Results The OsPT6- overexpressing rice lines grew better and accumulated more biomass than wild-type plants, and exhibited significant increases in P accumulation in various tissues, including reproductive tissues under both hydroponic and soil culture conditions. Phosphate-uptake experiment using radiolabeled Pi ( 33 P) showed that the rate of Pi uptake was 75 % and 73 % greater in transgenic plants grown under Pi-sufficient and -deficient conditions, respectively, than the wild-type controls, and that the shoot/root ratio of 33 P was 104 % and 42 % greater, respectively. In addition, the grain yield per transgenic plant was much higher than that of the wild-type plants under field conditions. Conclusions Taken together, our results demonstrate that OsPT6 plays a vital role in Pi acquisition and mobilization in rice and suggest that this gene may be used for genetic engineering rice plants that require less Pi fertilizer.

Description: Background and aims Knowledge related to extent of differing soil N forms and N transformation rates in subtropical southern China is severely limited. Accordingly, the purpose of this study was to investigate if and how tree species of different foliage types (coniferous, deciduous, and evergreen broadleaved) influence N forms and microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) content as well as gross N transformation rates in the organic and mineral soils of three distinct subtropical forests in China. Methods Chloroform fumigation extraction was used to determine MBC and MBN content while 15 N-isotope dilution techniques were used to measure gross N transformation rates. Canonical correspondence analysis (CCA) was used to quantify relationships between soil chemical characteristics and changes in soil N transformation rates. Results Soil N forms, MBC and MBN content, and N transformation rates were found to be significantly different between tree species. Deciduous forest soil exhibited the highest N transformation rates. Soil N transformation rates were closely associated with total soil C and N and MBC and MBN content. Conclusions Soil substrate quantity and soil microbial activity play a more important role in soil N transformation processes than does soil quality in China’s subtropical forests. Tree species type should therefore be taken into account when trying to determine ecosystem N cycling.

Description: Aims Responses to salt stress of two Gypsophila species that share territory, but with different ecological optima and distribution ranges, were analysed. G. struthium is a regionally dominant Iberian endemic gypsophyte, whereas G. tomentosa is a narrow endemic reported as halophyte. The working hypothesis is that salt tolerance shapes the presence of these species in their specific habitats. Methods Taking a multidisciplinary approach, we assessed the soil characteristics and vegetation structure at the sampling site, seed germination and seedling development, growth and flowering, synthesis of proline and cation accumulation under artificial conditions of increasing salt stress and effect of PEG on germination and seedling development. Results Soil salinity was low at the all sampling points where the two species grow, but moisture was higher in the area of G. tomentosa . Differences were found in the species’ salt and drought tolerance. The different parameters tested did not show a clear pattern indicating the main role of salt tolerance in plant distribution. Conclusions G. tomentosa cannot be considered a true halophyte as previously reported because it is unable to complete its life cycle under salinity. The presence of G. tomentosa in habitats bordering salt marshes is a strategy to avoid plant competition and extreme water stress.

Description: Background Water and nutritional restrictions are limiting factors for the growth of Eucalyptus trees in tropical climates. In the dry season, boron (B) uptake is severely affected. Aims The objectives of this study were to evaluate the phloem mobility of B and whether its deficiency can increase plant sensitivity to osmotic stress. It was also tested to what extent foliar application of B could mitigate the negative effects of drought under low B supply. Methods Seedlings of a drought tolerant Eucalyptus urophylla ( Blake , S. T .) clone were grown in nutrient solution, subjected to low availability of B for 25 days, and then submitted to a progressive osmotic stress. After imposition of osmotic stress, B was applied to young or mature leaves. Results B applications, mainly to mature leaf, stimulated root growth and delayed dehydration under osmotic stress and led to an increased B translocation and carbon isotopic composition. The expression of B transporters and pectin metabolism genes were also increased in water-stressed plants supplied with B by foliar application. Conclusions B deficiency led to increased plant dehydration and decreased root growth under osmotic stress. The application of B to mature leaf of water-stressed plants proved effective in mitigating the negative effects of water deficit in root growth.

Description: Background and Aims Tree species composition shifts can alter soil CO 2 and N 2 O effluxes. We quantified the soil CO 2 and N 2 O efflux rates and temperature sensitivity from Pyrenean oak, Scots pine and mixed stands in Central Spain to assess the effects of a potential expansion of oak forests. Methods Soil CO 2 and N 2 O effluxes were measured from topsoil samples by lab incubation from 5 to 25 °C. Soil microbial biomass and community composition were assessed. Results Pine stands showed highest soil CO 2 efflux, followed by mixed and oak forests (up to 277, 245 and 145 mg CO 2 -C m −2  h −1 , respectively). Despite contrasting soil microbial community composition (more fungi and less actinomycetes in pine plots), carbon decomposability and temperature sensitivity of the soil CO 2 efflux remain constant among tree species. Soil N 2 O efflux rates and its temperature sensitivity was markedly higher in oak stands than in pine stands (70 vs. 27 μg N 2 O-N m −2  h −1 , Q 10 , 4.5 vs. 2.5). Conclusions Conversion of pine to oak forests in the region will likely decrease soil CO 2 effluxes due to decreasing SOC contents on the long run and will likely enhance soil N 2 O effluxes. Our results present only a seasonal snapshot and need to be confirmed in the field.

Description: Background and aims Many rich fens are threatened by high nutrient inputs, but the literature is inconsistent with respect to the type of nutrient limitation and the influence of edaphic characteristics. Methods We performed experiments with N- and P-fertilization in three endangered rich fen types: floating fen with Scorpidium scorpioides , non-floating fen with Scorpidium cossonii , floodplain fen with Hamatocaulis vernicosus . In addition, K-fertilization was carried out in the floodplain fen. Results The floodplain fen showed no response to P-addition, but N- and K-addition led to grass encroachment and decline of moss cover and species richness. In contrast, in the P-limited floating fen with S. scorpioides , P-addition led to increased vascular plant production at the expense of moss cover. Scorpidium scorpioides , however, also declined after N-addition, presumably due to ammonium toxicity. The fen with S. cossonii took an intermediate position, with NP co-limitation. These striking contrasts corresponded with edaphic differences. The N-limited fen showed low Ca:Fe ratios and labile N-concentrations, and high concentrations of plant-available P and Fe-bound P. The P-limited fen showed an opposite pattern with high Ca:Fe ratios and labile N-concentrations, and low P-concentrations. Conclusions This implies that edaphic characteristics dictate the nature of nutrient limitation, and explain contrasting effects of N- and P-eutrophication in different fens.

Description: Aims Metal chemical forms and subcellular partitioning model (SPM) in organisms can provide valuable insights into metal toxicity. Methods Two cultivars of lettuce ( Lactuca sativa L.) were grown in Cd and Cu contaminated soils and chemical forms and subcellular distribution of Cd and Cu within the lettuce shoots were determined. Results Examination of the inhibition of superoxide dismutase (SOD) and catalase (CAT) activities, as well as the production of H 2 O 2 showed that Lactuca sativa L. var. longifolia is more sensitive to metal-stress than is Lactuca sativa L. var. crispa . In L. crispa , the majority of accumulated Cd was in the pectate- and protein-integrated forms (53.7–62.9 %), while in L. longifolia , a higher proportion of the Cd was in the water soluble forms (33.0–39.2 %) and in the organelles fraction – these forms being potentially associated with toxicity. The chemically-based chemical form approach agreed closely with independent biologically-based SPM, as demonstrated by their significant linear relationships. Conclusions This study provides a first step towards the integration of chemical form approach and SPM into a common mechanistic framework, which is important for predicting the likelihood of toxic effects of metals in the environment of interest.

Description: Background and Aims Increased plant density improves grain yield and nitrogen (N)–use efficiency in winter wheat ( Triticum aestivum L.) by increasing the root length density (RLD) in the soil and aboveground N–uptake (AGN) at maturity. However, how the root distribution and N–uptake at different soil depths is affected by plant density is largely unknown. Methods A 2–year field study using the winter wheat cultivar Tainong 18 was conducted by injecting 15  N–labeled urea into soil at depths of 0.2, 0.6, and 1.0 m under four plant densities of 135 m −2 , 270 m −2 ,405 m −2 , and 540 m −2 . Results We observed significant RLD and 15  N–uptake increases at each soil depth as the plant density increased from 135 to 405 m −2 . 15  N–uptake increased with plant density as the soil depth increased, although the corresponding RLD value fell with depth. The 15  N–uptake at each soil depth was positively related to the RLD at the same depth. The total AGN was positively related to RLD in deep soil, especially at 0.8–1.2 m. Conclusions Increasing the plant density from 135 m −2 to the optimum increases AGN primarily by increasing the RLD in deep soil and therefore increasing the plant density of winter wheat can be used to efficiently recover N leached to deep soil. Moreover, the total root numbers per unit area and RLD still increased at supraoptimal density while shoot number and N uptake stagnated.

Description: Background Meadows and shrublands are two major vegetation types on the Qinghai-Tibetan Plateau, but little is known about biochemical characteristics and its relation to decomposability of soil organic carbon (OC) under these two vegetation types. The present study was designed to evaluate effects of aspect-vegetation complex on biochemical characteristics and decomposability of soil OC. Methods Two hills were randomly selected; both with vegetation being naturally divided into southward meadows and northward shrublands by a ridge, and soils were sampled at depths of 0–15 and 15–30 cm, along contours traversing the meadow and shrubland sites. Particulate (particle size 2–0.05 mm) OC and nitrogen (N), microbial biomass C and N, non-cellulosic sugars, and CuO lignin were analyzed, and OC mineralization was measured for 49 days at 18 and 25 °C under laboratory incubation, respectively. Results More than half of soil OC was present as particulate fraction across all samples, indicating the coarse nature of soil organic matter in the region. Averaging over depths, shrublands contained 87.7 − 114.1 g OC and 7.7 − 9.3 g N per kg soil, which were 63 − 78 and 26 − 31 % higher than those in meadows, respectively. Meanwhile the C/N ratio of soil organic matter was 11.4 − 12.3 under shrublands, being 29 − 40 % higher than that under meadows. Soil OC under meadows was richer in noncellulosic carbohydrates and microbial biomass in the 0–15 and 15–30 cm depths but contained less lignin in the 15–30 cm depth. Ratios of microbially- to plant-derived monosaccharides and between acid and aldehyde of the vanillyl units were greater in soils under shrublands, showing more abundant microbially-derived sugars and microbially-transformed ligneous substances in OC as compared to meadow soils. By the end of 49 days’ incubation, total CO 2 –C evolution from soils under meadows was 15.0–16.2 mg g −1 OC averaging over incubation temperatures and soil depths, being 27–55 % greater than that under shrublands. Across all soil samples over two sites, total CO 2 − C evolved per g OC at either 18 or 25 °C was closely correlated to enrichments of noncellulosic carbohydrates and microbial biomass. This indicates that the greater soil OC decomposability under meadows was associated with its larger abundances of readily mineralizable fractions compared with shrublands. However, temperature increase effect on soil OC decomposability did not differ between the two types of vegetation. Conclusions Our findings suggest that the aspect-vegetation complex significantly affected pool size, biochemical characteristics, and decomposability of soil OC on the northeastern edge of Qinghai-Tibetan Plateau. However, the response of soil OC decomposability to temperature was similar between southward meadows and northward shrublands.

Description: Background and Aims Lespedeza cuneata (Dum. Cours.) G. Don is an invasive legume that displaces populations of native N. American congeners. Our aims are to determine the growth benefits of different rhizobacterial strains for L. cuneata and native Lespedeza virginica (L.) Britton, and to determine if these strains influence competition between these plants. Methods Plants were grown under nitrogen-limiting conditions in sterilized soil in pairs consisting of two L. cuneata , two L. virginica , or one of each species, and then plants were inoculated with one of seven rhizobial isolates, or with a no-strain control. After 3 months, plants were harvested for determination of biomass and nodulation rate. Results Five of the assayed stains improved L. cuneata biomass over uninoculated controls, but none of the strains benefited L. virginica. L. cuneata plants had more biomass and root nodules when grown in competition with L. virginica than with a conspecific. Conclusions Asymmetrical benefits from these symbionts accrued to invasive L. cuneata but not to native L. virginica , and this may provide the invader with a growth advantage in the field. Changes in the availability of effective symbionts in the soils of invaded sites can shape performance of native and invasive plants.

Description: Background and Aims Numerous studies noted that the seed banks of drained former wet-meadows did not have enough residual seed potential for the successful restoration of species-rich fen-meadows. However, it is unclear whether a decline in groundwater level exerts a negative effect on the seed survival of wet-meadow plant species in the soil. This paper assessed the dependence of soil seed survival on different groundwater levels. Methods We tested the influence of the groundwater level on the seed survival rate of 8 wet-meadow plant species in fen lysimeters with constant groundwater levels of 5, 30 and 70 cm. Seeds were buried in nylon mesh bags at 2 depths (5 and 25 cm), exhumed after 1, 3 and 5 years in the spring and tested in a climate chamber for germinable seeds under conditions of different day-night rhythms and fluctuating temperatures. Results At both burial depths, more viable seeds survived at lower groundwater levels compared with groundwater levels near the surface. Waterlogged conditions resulted in a significant reduction in the number of germinable seeds for most of the studied plant species. A cluster analysis divided the eight plant species into three groups which differed in soil seed bank persistence and tolerance towards soil wetness. Conclusions The decline of the groundwater level due to fen-meadow drainage does not negatively affect the seeds of wet-meadow plant species. Our results also suggest that for some species, the classification of soil seed bank type may vary according to the groundwater level dynamic of the location.

Description: Background and aims The framework of root system architecture is shaped by the three-dimensional (3D) trajectory of the axile roots. However, methods for characterising root trajectory in the field are lacking. Our aim was to develop a new method for quantifying the spatial distribution of axile roots of maturing plants. Methods The trajectory of axile roots of two maize cultivars was measured using a 3D digitiser in situ in the field, in parallel with diameter measurements along the same roots based on scanned images. The measured diameters were then mapped onto the digitised trajectory. Results We show that inter-plant distances did not influence root trajectory in either cultivar. The two cultivars had different initial angles from the vertical and presented slightly different patterns of root angle distribution. The reorientation of an axile root downwards was related to its angle and diameter, which can serve as a valuable resource for the parameterisation of root architecture models. Conclusions The method is suitable for accurate determination of the 3D architecture of axile roots of mature maize plants under field conditions. The value of acquiring a relative complete root trajectory is highlighted.

Description: Background Our previous studies documented how soil CO 2 efflux, one of the main carbon pathways in forest ecosystems, is affected by soil moisture and forest structure in an aseasonal tropical rainforest in Borneo, Malaysia. Aim In this study, we clarify the effect of short-term drought treatment on the spatial variation of soil CO 2 efflux in a forest, and to interpret the changes in soil CO 2 efflux caused by root activities. Methods Experimental plots (15 m radius) were established around six emergent trees and a drought treatment was conducted for three of the six plots. Soil CO 2 efflux was measured along with environmental factors and root biomass, respiration and production in each plot. Results Soil CO 2 efflux at 0.5 m of the emergent trees was nearly three times higher than at 5 and 10 m away from the trees. Root respiration and biomass had no correlation with the spatial variation. Soil water content decreased by nearly 30 % during the drought treatment, although soil CO 2 efflux was unchanged between drought and control plots. Conclusions Our result suggests a strong spatial variation exists in soil CO 2 efflux around emergent trees, but short-term severe drought has little effect on it.

Description: Background and aims The knowledge of soil water storage is vital for rational agricultural management, and in soil-plant-water relations. This study was conducted to evaluate the temporal processes of soil water status of a sugarcane field under residue management during the 2011/2012 and 2012/2013 growing seasons in southern Brazil. Methods Soil water storage (SWS) and matric potential (Ψ) were monitored in the 0–10 and 10–20 and 40–60 cm layers using time domain reflectometer sensors and tensiometers while precipitation (P) and potential crop evapotranspiration (ET) were obtained using rainguage and daily weather data. Results There was significant temporal variation of soil water status with soil depths. SWS was lower while matric potential was higher in no mulch treatment than in mulched treatment in both growing seasons. SWS cross-correlated with other variables, however, results were not the same for the different soil depths and treatments. Classical regression of SWS from combinations of log (Ψ), ET and P gave satisfactory results, however state-time analysis was better with higher R 2 values and incorporated errors. Conclusions State-time analysis, combined with state-space could be a useful tool for good predictions of soil water status. Residue mulching influenced soil water status, thus proved to be a sustainable soil management practice.

Description: Background and aims Grassland abandonment followed by forest succession is the dominant land-use change in the European Alps. We studied the impact of current forest expansion on mountain grassland on changes in physical soil organic carbon (SOC) fractions along a land-use and management gradient, focusing on changes in aggregate stability and particulate organic matter (POM). Methods Four successional stages were investigated: managed grassland, two transitional phases in which grassland abandonment led to colonization by Picea abies (L.) Karst., and old mixed forest dominated by Fagus sylvatica L. and P. abies . Soil samples collected from the mineral soil (0–5 cm, 5–10 cm, 10–20 cm) were fractionated following two procedures: 1) aggregate size fractionation, separating aggregates based on their dimension, and 2) size-density fractionation, separating stable aggregates from non-occluded POM. Results The dimension of aggregates assessed by aggregate size fractionation tended to increase, whereas SOC allocation to stable aggregates assessed by size-density fractionation decreased following conversion of grassland to forest (e.g. from 81 to 59 % in the 0–5 cm layer). The amount of SOC stored in POM increased by 3.8 Mg ha −1 in the integrated 0–20 cm layer from managed grassland to old forest. Conclusions The combination of two physical SOC fractionation procedures revealed that natural forest succession on abandoned grasslands led to a decline in physical SOC stability in the mineral soil, suggesting that SOC can become more susceptible to management and environmental change.

Description: Aims Two contrasting canopy manipulations were compared to unpruned controls on London plane trees, to determine the effects on canopy regrowth, soil and leaf water relations. Methods ‘Canopy reduction’, was achieved by removing the outer 30 % length of all major branches and ‘canopy thinning’, by removing 30 % of lateral branches arising from major branches. Results Total canopy leaf areas recovered within two and three years of pruning for the canopy-thinned and reduced trees respectively. Canopy reduction increased mean leaf size, nitrogen concentration, canopy leaf area density and conserved soil moisture for up to 3 years, whereas canopy thinning had no effects. Another experiment compared more severe canopy reduction to unpruned trees. This produced a similar growth response to the previous experiment, but soil moisture was conserved nearer to the trunk. Analysis of 13 C and 18 O signals along with leaf water relations and soil moisture data suggested that lower boundary layer conductance within the canopy-reduced trees restricted tree water use, whereas for the canopy-thinned trees the opposite occurred. Conclusions Only canopy reduction conserved soil moisture and this was due to a combination of reduced total canopy leaf area and structural changes in canopy architecture.