ALBERT

Description: Aims Afforestation causes important alterations in SOM content and composition that affect the soil functions and C balance. The aim of this study was to identify the mechanisms that determine the changes in SOM composition following afforestation of grasslands. Methods The study included 4 chronosequences and 5 paired plots comprising pastures and land afforested with Pinus radiata . The SOM was characterized by 13 C CP-MAS NMR spectroscopy and differential scanning calorimetry. Results During the first 10–20 year after afforestation, the changes in SOM content varied from slight gains to large losses (〉40 %). The analyses revealed that even SOM compounds considered resistant to decomposition were degraded during this time. The SOM gains, observed 20 year after stand establishment, were favoured by the higher recalcitrance of pine litter and possibly by soil acidification. The concentrations of most SOM compounds, particularly the stable compounds, were higher at the end of the rotation. The low degree of protection, along with the favourable climatic conditions, may also explain the rapid decomposition of SOM, including resistant compounds, in these soils. DSC analysis complemented the information about SOM composition provided by other techniques. Conclusions The accumulation of stable SOM compounds at the end of the rotation suggests a longer soil C turnover in these afforested soils, which may alleviate the gradual loss of SOC in intensively managed forest soils.

Description: Background and aims Plant nutrient uptake from coarse soil (2–4 mm diameter) has been demonstrated for only a limited number of nutrients, and the nutritional contribution of coarse soil when present with fine soil (material 〈2 mm diameter) in realistic ratios is unknown. We conducted a seedling pot trial to investigate the functional relevance of this soil fraction to plant nutrition. Methods Fine soil was mixed with either coarse soil, or the equivalent volume of inert glass chips, in ratios identical to those occurring naturally in soil sampled from two depths at each of two sites. Seedlings of Nothofagus solandri var. cliffortioides and Weinmannia racemosa were planted in the soil mixtures and harvested after 9 months. Results The content of nitrogen, phosphorous, potassium, magnesium and other elements in the above ground seedling tissue was significantly increased by the presence of coarse soil. The coarse soil fraction also contributed proportionally much more to plant nutrient uptake than fine soil on a mass per mass basis. Conclusions Coarse soil is excluded from conventional soil analysis, so is possible that soil nutrient capital is systematically underestimated. This has implications for land management and studies of plant dynamics in relation to nutrient supply.

Description: Background and aims Lateral tree-scale variability in plantations should be taken into account when scaling up from point samples, but appropriate methods for sampling and calculation have not been defined. Our aim was to define and evaluate such methods. Methods We evaluated several existing and new methods, using data for throughfall, root biomass and soil respiration in mature oil palm plantations with equilateral triangular spacing. Results Three ways of accounting for spatial variation within the repeating tree unit (a hexagon) were deduced. For visible patch patterns, patches can be delineated and sampled separately. For radial patterns, measurements can be made in radial transects or a triangular portion of the tree unit. For any type of pattern, including unknown patterns, a triangular sampling grid is appropriate. In the case studies examined, throughfall was 79 % of rainfall, with 95 % confidence limits being 62 and 96 % of rainfall. Root biomass and soil respiration, measured on a 35-point grid, varied by an order of magnitude. In zones with steep gradients in parameters, sampling density has a large influence on calculated mean values. Conclusions The methods defined here provide a basis for representative sampling and calculation procedures in studies requiring scaling up from point sampling, but more efficient methods are needed.

Description: In Central Cameroon cocoa is mainly produced by household farming systems based on complex associations between cocoa and companion trees. Setup either on native/remnant forest or savannah, these agroforestry systems (AFS) are managed according their geographical position and local pedoclimatic conditions. In this paper, we investigated the effects of local management strategies on carbon (C) storage of live trees in three different cocoa production zones of Central Cameroon. In the 58 fields studied, 8,996 cocoa trees and 1,258 companions were surveyed. Tree sampling was non-destructive and to estimate C storage we used allometric models for above- and belowground biomasses. We measured abundance, height, diameter at breast height and determined species of companion trees. We distinguished between four cocoa plantation age categories (immature, young, mature and senescent) and three preceding systems (forest, forest gallery and savannah). We surveyed farmers’ use of each associated tree, allocated it to a functional category and asked if it had been introduced or conserved. Total C content of live trees was on average close to 70 t ha −1 . We found that it mostly relied on associated trees—cocoa trees contribution being ac. 2–12 % of live trees total C. The level of contribution to C storage of companions from different use categories differed between sites—trees producing food had contributed most in Bokito and Obala while trees used for shading or fertility contributed most in Ngomedzap. Dynamics of C storage in live trees was found to be independent from cocoa trees growth and age. When aging, AFS continuously lost companion trees and especially conserved ones putatively because of farmers’ selective logging. Yet, AFS apparently maintained equivalent C storage abilities with time. Hence, even if cocoa do not contribute significantly to C storage in our study, the systems into which they are included are able to significantly store C and may also contribute to other ecological services such as conservation.

Description: An efficient technology capable of cloning superior Jatropha curcas germplasm through grafting on large scale was standardized. This technique overcomes the bottlenecks associated with conventional seed and cutting raised plants. This is a novel technique being capable of establishing well-rooted pure strands of superior genotype utilising stock–scion concept and also explores possibilities for the improvement of existing inferior strands into high yielding and superior varieties. Among the various grafting methods tried, top cleft grafting was found to be most successful. The ideal stock–scion diameter and grafting height was found to be 3–4 cm and 40–60 cm, respectively. Top cleft grafting was more successful, stable and strong in comparison to other grafting methods, exhibiting 92.0 and 94.09 % success during spring and monsoon seasons, respectively. Side cleft grafting proved to be the second best method resulting in 80.0 and 82.23 % success during spring and monsoon seasons, respectively.

Description: Nutrient losses during slash-and-burn clearing in tropical forests, coupled with demand by food crops, can deplete nutrients and result in crop abandonment after 1–2 years. Slash-and-mulch technology prevents nutrient losses from burning, while mulch decomposition may serve as a nutrient source. This research investigates the release of nutrients from the mulch and potential uptake of released N by plant biomass after a multi-species agroforestry system was planted in June 2005, following the clearing of a 1 ha of 7-year-old forest with a mulching tractor in Igarapé Açu, Brazil. The study evaluated soil conditions, mulch decomposition, and nutrient concentrations of Manihot esculenta and native vegetation under treatments of P+K fertilization in combination with four native tree species and N-fixing Inga edulis , or with three native tree species without I. edulis . Mulch layer N, Ca and Mg content decreased in response to fertilization, while mulch layer P and K content increased. Nutrient content increased in M. esculenta stems and tubers with fertilization and in the presence of I. edulis , and in competing vegetation with fertilization. Estimated tree N content increased 311 % with fertilization, but by 154 % in the presence of I. edulis . Fertilization with P+K, as well as the presence of I. edulis , increased N stocks in total biomass.

Description: Background Plants must acquire at least 14 mineral nutrients from the soil to complete their life cycles. Insufficient availability or extreme high levels of the nutrients significantly affect plant growth and development. Plants have evolved a series of mechanisms to adapt to unsuitable growth conditions where nutrient levels are too low or too high. microRNAs (miRNAs), a class of small RNAs, are known to mediate post-transcriptional regulation by transcript cleavage or translational inhibition. Besides regulating plant growth and development, miRNAs are well documented to regulate plant adaptation to adverse environmental conditions including nutrient stresses. Scope In this review, we focus on recent progress in our understanding of how miRNAs are involved in plant response to stresses resulting from deficiency in nutrients, such as nitrogen, phosphorus, sulfur, copper and iron, as well as toxicities from heavy metal ions. Conclusions Accumulated evidence indicates that miRNAs play critical roles in sensing the abundance of nutrients, controlling nutrient uptake and phloem-mediated long-distance transport, and nutrient homeostasis. miRNAs act as systemic signals to coordinate these physiological activities helping plants respond to and survive nutrient stresses and toxicities. Knowledge about how miRNAs are involved in plant responses to nutrient stresses promise to provide novel strategies to develop crops with improved nutrient use efficiency which could be grown in soils with either excessive or insufficient availability of nutrients.

Description: Background and aims (i) compare the concentrations of total polyphenols (TP) and condensed tannins (CT), and CT profiles in different organs of mature trees and seedlings of eight true mangrove species in Hong Kong; (ii) examine the antioxidant activities of CT and (iii) relate the non-enzymatic antioxidative defence system with the vertical zonation pattern of mangrove species. Methods Mature trees and seedlings of eight species were collected from a Hong Kong mangrove swamp to determine TP and CT concentrations and the antioxidant activities of CT. Results According to TP concentrations, the true mangrove species could be broadly classified into three groups, (i) Lumnitzera racemosa and Aegiceras corniculatum 〉 (ii) Heritiera littoralis , Excoecaria agallocha , Bruguiera gymnorrhiza and Kandelia obovata 〉 (iii) Acanthus ilicifolius and Avicennia marina . The last two are pioneer species in the most foreshore location. They also had significantly lower antioxidant activities, CT concentrations and different CT profiles than the other six species in mid- and low-tides. Conclusions Classification of the eight true mangrove species into three groups based on polyphenols was similar to their vertical zonation from land to sea. The relationships between these antioxidants and zonation should be further verified by transplantation studies.

Description: Background and aims Soil phosphorus (P) indices that have been originally developed and applied to agricultural soils for predicting P uptake by plants were examined in a pot experiment to determine the most suitable index for P availability in bauxite-processing residue sand (BRS). Methods Pot trials with ryegrass were established using BRS that had been amended with various organic (greenwaste compost, biochar and biosolids) and inorganic (zeolite) materials and different levels of di-ammonium phosphate fertiliser. Soil P availability indices tested included anion-exchange membrane (AEM-P), 0.01 M calcium chloride (CaCl 2 -P), Colwell-P, and Mehlich 3-P. Results AEM-P was found to most closely reflect the available P status in BRS across all treatments, and had the strongest associations with plant P uptake compared to Colwell-P, Mehlich 3-P and CaCl 2 -P. AEM-P was more closely correlated with P uptake by ryegrass than other P indices, while Colwell-P was closely related to leaf dry matter. Interestingly, a strong inverse relationship between plant indices and pH in BRS growth media was observed, and an adequate level of plant P uptake was found only in 15 year-old rehabilitated BRS with pH 〈 8.0. Conclusions AEM-P was found to be the most suitable index for evaluating P availability in highly alkaline BRS and pH was an important parameter affecting uptake of P by ryegrass. Importantly, time is required (〉 5 years) before improved uptake of P by plants can be observed in rehabilitated residue sand embankments.

Description: Background & aims Herbivore-driven changes to soil properties can influence the decomposition rate of organic material and therefore soil carbon cycling within grassland ecosystems. We investigated how aboveground foraging mammalian and invertebrate herbivores affect mineral soil decomposition rates and associated soil properties in two subalpine vegetation types (short-grass and tall-grass) with different grazing histories. Methods Using exclosures with differing mesh sizes, we progressively excluded large, medium and small mammals and invertebrates from the two vegetation types in the Swiss National Park (SNP). Mineral soil decomposition rates were assessed using the cotton cloth (standard substrate) method between May and September 2010. Results Decomposition displayed strong spatio-temporal variability, best explained by soil temperature. Exclusion of large mammals increased decomposition rates, but further exclusion reduced decomposition rates again in the lightly grazed (tall-grass) vegetation. No difference among treatments was found in the heavily grazed (short-grass) vegetation. Heavily grazed areas had higher decomposition rates than the lightly grazed areas because of higher soil temperatures. Microbial biomass carbon and soil C:N ratio were also linked to spatio-temporal decomposition patterns, but not to grazing history. Conclusions Despite altering some of the environmental controls of decomposition, cellulose decomposition rates in the SNP’s subalpine grasslands appear to be mostly resistant to short-term herbivore exclusion.

Description: Background Our recent publication (Warren et al., Plant Soil 366:683–693, 2013 ) described how pulses of deuterium oxide (D 2 O) or H 2 O combined with neutron radiography can be used to indicate root water uptake and hydraulic redistribution in maize. This technique depends on the large inherent differences in neutron cross-section between D and H atoms resulting in strong image contrast. Scope and Conclusions However, as illustrated by Carminati and Zarebanadkouki ( 2013 ) there can be a change in total water content without a change in contrast simply by a change in the relative proportions of D 2 O and H 2 O. We agree with their premise and detailed calculations (Zarebanadkouki at al. 2012 , 2013 ), and present further evidence that mixing of D 2 O and H 2 O did not confound evidence of hydraulic redistribution in our study.

Description: Background and aims The growth of green plants depends not only on photosynthesis, but also on the successful remobilization and translocation of seed phosphorus (P) reserves to the vegetative parts of the developing seedling during early growth. Remobilization and photosynthesis are therefore two parallel and co-coinciding processes involved in better seedling establishment and early growth. Methods A study was conducted to evaluate the priority of developing maize seedlings to translocate the remobilized seed P reserves and external P uptake to seedling root and shoot sinks during 4 weeks of early growth. Two fluxes of P in growing seedlings, one from seed remobilized P reserves and one from external P uptake, were distinguished by labelling external nutrient solution P with 32 P. Results The seedling phytomass was equally distributed between seedling roots and shoots for 530 cumulated degree days after sowing. Seedlings partitioned up to 71 % of P from seed reserves and up to 68 % of P acquired from the nutrient solution, to the shoots, depending on the seed P content and P concentration in the nutrient solution. It appears that accumulation of P slows down in seedling roots corresponds to the translocative functions of root P towards shoots for start of photosynthesis. Conclusions Our results suggest that the major part of seed P reserves and external P uptake were used in early development of the seedling and the preferred sink was seedling shoots.

Description: Background and aims Nickel (Ni) has become a major heavy metal contaminant. The form of nitrogen nutrition remarkably affects IRT1 expression in roots. IRT1 has an activity of transporting Ni 2+ into root cells. Therefore, nitrogen-form may affect Ni accumulation and toxicity in plants. The assumption was investigated in this study. Methods The Arabidopsis plants were treated in Ni-contained growth solutions with either nitrate (NO 3 − ) or ammonium (NH 4 + ) as the sole N source. After 7-day treatments, Ni concentration, IRT1 expression, Ni-induced toxic symptoms and oxidative stress in plants were analyzed. Results The NO 3 − -fed plants contained a higher Ni concentration, had a greater IRT1 expression in roots, and developed more severe toxic symptoms in the youngest fully expanded leaves, compared with the NH 4 + -fed plants. The Ni-induced growth inhibition was also more significant in NO 3 − -fed plants. Interestingly, Ni exposure resulted in greater hydrogen peroxide (H 2 O 2 ) and superoxide radical (O 2 . − ) accumulations, more severe lipid peroxidation and more cell death in NO 3 − -fed plants, whereas the opposite was true for NH 4 + -fed plants. Furthermore, the Ni-enhanced peroxidase (POD) and superoxide dismutase (SOD) activities were greater in NO 3 − -fed plants Conclusion NO 3 − nutrition promotes Ni uptake, and enhances Ni-induced growth inhibition and oxidative stress in plants compared with NH 4 + nutrition.

Description: Background and aims Brassica napus has high boron (B) demand, but significant genotype differences exist with respect to B deficiency. The aim of this research was to elucidate the relationship between the different sensitivities of Brassica napus cultivars to low B stress and the characteristics of B uptake and transport to characterise the regulation of B efficiency in Brassica napus . Methods B-efficient and B-inefficient Brassica napus cultivars were used to compare the uptake and transport of B using the stable isotope 10 B tracer and grafting experiments, as well as expression of B transporters by RT-PCR. Results B-efficient cultivars have significant advantages with regard to B limitation. The B-efficient cultivar HZ showed less severe B deficiency symptoms and higher dry biomass than the B-inefficient cultivars LW and LB. Both the amount of total B and the 10 B concentration and accumulation in the shoots and roots of B-efficient HZ were higher than those of B-inefficient cultivars. In B-inefficient LW, the amount of total B and the 10 B that was transported into shoots was less than in the other three cultivars and the content and accumulation of total B and 10 B in the roots of B-inefficient LB were the lowest among all of the cultivars. When the roots of B-efficient HZ were used as stocks, the grafted plants showed B-efficient characteristics, such as mild B deficiency symptoms, and higher dry biomass and B accumulation, regardless of whether they originated from B-efficient or B-inefficient cultivars. In contrast, the grafted plants with B-inefficient LW used as stocks were B-inefficient. The expressions of BnBOR1;1c , BnBOR1;2a and BnNIP5;1 were up-regulated in roots under low B stress compared with the normal B condition. However, there was no obvious difference in the expressions of the three genes or of four other BnBOR1s between B-efficient and B-inefficient cultivars in low or normal B environments. Conclusions These results indicate that the B efficiency of Brassica napus is controlled primarily by roots, which allow more uptake and accumulation of B in B-efficient cultivars than B-inefficient cultivars in a low B environment. However the molecular mechanism regulating B efficiency in Brassica napus remains to be determined.

Description: Aims Application of carbon (C) and nitrogen (N) isotopes is an essential tool to study C and N flows in plant-soil-microorganisms systems. When targeting single plants in a community the tracers need to be added via e.g., leaf-labeling or stem-feeding approaches. In this study we: (i) investigated if bicarbonate can be used to introduce 14 C (or 13 C) into white clover and ryegrass, and (ii) compared the patterns of 14 C and 15 N allocation in white clover and ryegrass to evaluate the homogeneity of tracer distribution after two alternative labeling approaches. Methods Perennial ryegrass and white clover were pulse labeled with 15 N urea via leaf-labeling and 14 C either via a 14 CO 2 atm or with 14 C bicarbonate through leaf-labeling. Plants were sampled 4 days after labeling and prepared for bulk isotope analysis and for 14 C imaging to identify plant parts with high and low 14 C activity. Subsequently, plant parts with high and low 14 C activity were separated and analyzed for 15 N enrichment. Results Bicarbonate applied by leaf-labeling efficiently introduced 14 C into both white clover and ryegrass, although the 14 C activity in particular for white clover was found predominantly in the labeled leaf. Using 14 C imaging for identification of areas with high (hotspots) and low 14 C activity showed that 14 C was incorporated very heterogeneously both when using bicarbonate and CO 2 as expected when using pulse labeling. Subsequent analysis of 15 N enrichment in plant parts with high and low 14 C activity showed that 15 N also had a heterogeneous distribution (up to two orders of magnitude). Conclusion Bicarbonate can efficiently be used to introduce 14 C or 13 C into plant via the leaf-labeling method. Both 14 C and 15 N showed heterogeneous distribution in the plant, although the distribution of 15 N was more even than that of 14 C.

Description: Background and aim In numerous areas, rice cultivated under flooded conditions is exposed simultaneously to iron excess and arsenic contamination. The impact of these combined stresses on yield-related parameters and As distribution and speciation in various plant parts remains poorly documented. Methods Rice (cv I Kong Pao) was exposed to iron excess (125 mg L −1 Fe 2 SO 4 ), arsenic (50 and 100 μM Na 2 HAsO 4 .7H 2 O) or a combination of those stressing agents in hydroponic culture until harvest. Plant growth, yield-related parameters, non protein thiols concentration and mineral nutrition were studied in roots and shoots. Arsenic speciation was determined by high-performance liquid chromatography-hydride generation-atomic fluorescence spectrometry. Key Results Iron excess increased As retention by the roots in relation to the development of the root iron plaque but decreased As accumulation in the shoot. Arsenic concentration was lower in the grains than in the shoots. Iron stress reduced As accumulation in the husk but not in the dehusked grains. Iron excess decreased the proportion of extractable As(III) and As(V) in the grain while it increased the proportion of extractable As(III) in the shoot. Combined stresses (Fe+As) affected plant nutrition and significantly reduced the plant yield by limiting the number of grains per plant and the grain filling. Conclusions Fe excess had an antagonist impact on shoot As concentration but an additive negative impact on several yield-related parameters. Iron stress influences both As distribution and As speciation in rice.

Description: Background and aims Intermittently frozen ground in winter is expected to disappear over large areas in the temperate zone due to ongoing climate warming. The lack of soil frost influences plant soil interactions and needs to be studied in more detail. Methods Winter soil frost was avoided by belowground heating wires in a field experiment over two subsequent winters in a temperate grassland. Soil respiration, soil nitrogen availability and plant performance (aboveground biomass, root length at two depth levels, greenness, nutrient content) were compared between “no-frost” and reference plots which underwent repeated freeze-thaw cycles in both winters. Results Soil respiration increased in the “no-frost” treatment during the warming phase (+291 %). N-availability in the upper 10 cm of the soil profile was not affected, possibly due to increased plant N accumulation during winter (+163 %), increased plant N concentration (+18 %) and increased biomass production (+31.5 %) in the growing season. Translocation of roots into deeper soil layers without changes in total root length in response to the “no-frost” treatment, however, may be a sign of nutrient leaching. Conclusions The cumulative effect on carbon cycling due to warmer soils therefore depends on the balance between increased winter carbon loss due to higher soil biotic activity and enhanced plant productivity with higher nutrient accumulation in the growing season.

Description: Aims The aims of this work were to investigate the aluminum (Al) and phosphate (P) interactions in the regulation of root system architecture of Arabidopsis thaliana seedlings and the contribution of auxin signaling in primary and lateral root growth in response to Al toxicity. Methods Detailed analyses of root system architecture and cell division were performed in Arabidopsis WT seedlings and in low phosphorus insensitive mutants lpi1 - 3 and lpr1 - 1 lpr2 - 1 in response to Al. Expression studies of P-deficiency regulated phosphate transporter AtPT2 were also conducted. The role of auxin as a mediator of root morphogenetic changes by Al was evaluated by using the auxin-signaling mutants tir1 , tir1 afb2 afb3 , and arf7 arf19 . Results Al inhibited primary root growth by affecting cell cycle progression and causing differentiation of cells in the root meristem. These effects were reduced in low phosphorus insensitive lpi1 - 3 and low phosphate resistant lpr1 - 1 lpr2 - 1 Arabidopsis mutants. Al also activated the expression of the low phosphate-induced P transporter AtPT2 in roots. Lateral root formation by Al decreased in tir1 afb2 afb3 while arf7 arf19 mutants were highly resistant to Al in both primary root inhibition and lateral root induction. Conclusions Our results suggest that lateral root formation in response to Al toxicity and P deficiency may involve common signaling mechanisms, while a pathway involving ARF7 and ARF19 is important for primary root growth inhibition by Al.

Description: Aims Litter decomposition and subsequent nutrient release play a major role in forest carbon and nutrient cycling. To elucidate how soluble or bulk nutrient ratios affect the decomposition process of beech ( Fagus sylvatica L.) litter, we conducted a microcosm experiment over an 8 week period. Specifically, we investigated leaf-litter from four Austrian forested sites, which varied in elemental composition (C:N:P ratio). Our aim was to gain a mechanistic understanding of early decomposition processes and to determine microbial community changes. Methods We measured initial litter chemistry, microbial activity in terms of respiration (CO 2 ), litter mass loss, microbial biomass C and N (C mic and N mic ), non purgeable organic carbon (NPOC), total dissolved nitrogen (TDN), NH 4 + , NO 3 - and microbial community composition (phospholipid fatty acids – PLFAs). Results At the beginning of the experiment microbial biomass increased and pools of inorganic nitrogen (N) decreased, followed by an increase in fungal PLFAs. Sites higher in NPOC:TDN (C:N of non purgeable organic C and total dissolved N), K and Mn showed higher respiration. Conclusions The C:N ratio of the dissolved pool, rather than the quantity of N, was the major driver of decomposition rates. We saw dynamic changes in the microbial community from the beginning through the termination of the experiment.

Description: Background and aims Grazing may influence nutrient cycling in several ways. In productive mountain grasslands of central Argentina cattle grazing maintain a mosaic of different vegetation patches: lawns, grazed intensively and dominated by high quality palatable plants, and open and closed tussock grasslands dominated by less palatable species. We investigated if differences in the resources deposited on soil (litter and faeces) were associated with litter decomposition rates and soil nitrogen (N) availability across these vegetation patches. Methods We compared the three vegetation patches in terms of litter and faeces quality and decomposability, annual litterfall and faeces deposition rate. We determined decomposition rates of litter and faces in situ and decomposability of the same substrates in a common garden using “litter bags”. We determined soil N availability (with resin bags) in the vegetation patches. Also, we performed a common plant substrates decomposition experiment to assess the effect of soil environment on decomposition process. This technique provides important insights about the soil environmental controls of decomposition (i.e. the sum of soil physicochemical and biological properties, and microclimate), excluding the substrate quality. Results The litter quality and faeces deposition rate were higher in grazing lawns, but the total amounts of carbon (C) and nitrogen (N) deposited on soil were higher in tussock grasslands, due to higher litterfall in these patches. The in situ decomposition rates of litter and faeces, and of the two common plant substrates were not clearly related to either grazing pressure, litterfall or litter quality (C, N, P, lignin, cellulose or hemicellulose content). In situ litter decomposition rate and soil ammonium availability were correlated with the decomposition rates of both common plant substrates. This may suggest that difference in local soil environment among patch types is a stronger driver of decomposition rate than quality or quantity of the resource that enter the soil. Conclusions Our results show that, although high grazing pressure improves litter quality and increases faeces input, the reduction in biomass caused by herbivores greatly reduces C and N input for the litter decomposition pathway. We did not find an accelerated decomposition rate in grazing lawns as proposed by general models. Our results point to soil environment as a potential important control that could mask the effect of litter quality on field decomposition rates at local scale.

Description: Background and aims Cd uptake has been shown to increase during conditions of Fe deficiency. This study tested the hypothesis that Fe-deficiency-responsive genes, particularly OsNRAMP1, play a role in the increased Cd uptake that occurs when rice is grown in aerobic soil conditions. Methods Plants were grown in aerobic or flooded soil conditions. Uptake of Cd was compared to levels of expression of candidate metal transporters and to metal ion availability in soil. Results Plants grown with intermittent soil flooding experienced a predominantly aerobic root environment and had the highest plant Cd uptake. Stronger upregulation of OsNRAMP1 was detected in plants grown in unflooded soil than in flooded soil. However, these transcriptional responses were not linked to an increase in Cd uptake. Overexpression of OsNRAMP1 was not found to increase the uptake of Cd in rice in soil or solution culture. In contrast, there were large differences in availability of Cd, Fe and Mn between flooded and aerobic soils, which were linked to changes in Cd uptake. Conclusions Aerobic soil conditions favour Cd uptake through increased Cd availability and decreased competition between Cd and Fe rather than through the increased expression of the Fe transporters themselves.

Description: Background and aims Intensive land use has led to degradation and abandonment of Portuguese oak woodlands, and subsequent shrub encroachment may have altered the spatial heterogeneity of soil C and N pools. The aim of this study was to evaluate the effects of shrub invasion on soil C and N dynamics in an oak woodland in Southern Portugal. Methods Soil was sampled beneath and outside scattered Quercus suber L. canopies, considering non-encroached areas and areas encroached by shrubs ( Cistus ladanifer L. or Cistus salviifolius L.). Results The spatial heterogeneity of soil C and N contents was mainly associated with tree presence. Outside tree canopies, the labile C pools were larger (mainly beneath C . ladanifer ) and C cycling was faster in encroached areas than in non-encroached areas. Net and gross N mineralization and urease and protease activities were also higher in encroached than in non-encroached areas; however, the metabolic quotient and the Cmicrobial/Corganic ratio were not significantly affected. Beneath the tree canopy, significant effects of encroachment included a small increase in soil labile C and the enzymatic activity beneath C . ladanifer . Conclusions The results indicate the potential capacity of shrub encroachment to accumulate soil organic C in the long term. The rate of soil C and N turnover promoted by shrub encroachment may depend on the Cistus species present.

Description: Aims Decreased expression of TaNAM genes by RNAi results in delayed senescence and decreased grain protein, iron, and zinc concentrations. Here, we determined whether NAM expression level alters onset of senescence under stress conditions, whether delayed senescence in the TaNAM -RNAi line resulted in improved tolerance to post-anthesis abiotic stress, and determined the effects of post-anthesis abiotic stress on N and mineral remobilization and partitioning to grain. Methods Greenhouse-grown WT and TaNAM -RNAi wheat were characterized in two studies:three levels of N fertility or water limitation during grain fill. Studies were conducted under both optimal and heat stress temperatures. Senescence onset was determined by monitoring flag leaf chlorophyll. Results Under optimal tempertures, TaNAM -RNAi plants had a yield advantage at lower N. TaNAM -RNAi plants had delayed senescence relative to the WT and lower grain protein and mineral concentrations, N remobilization efficiency, and partitioning of N and most minerals to grain. Conclusions Nutritional quality of TaNAM -RNAi grain was consistently lower than WT. Delayed senescence of TaNAM -RNAi plants provided a yield advantage under optimal temperatures but not under water or heat stress. Discovery of specific NAM protein targets may allow separation of the delayed senescence and nutrient partitioning traits, which could be used for improvement of wheat.

Description: Aims Nitrification inhibitors (NI) formulated on granulated ammonium sulphate nitrate (ASN) are an option to minimize nitrate leaching into ground waters and emissions of the greenhouse gas N 2 O. This paper focuses (a) on the development of an analytic enabling to extract and quantify the NI 3,4-dimethylpyrazolephosphate (DMPP), marketed since 1999. The efficiency of DMPP has been studied in laboratory and field soils. Here the DMPP analytic and the behaviour of a nitrifying bacterial consortium enriched from a field soil and exposed to zero, field applied and a 10 fold higher DMPP concentration than the recommended one for field application are in the focus. Methods For extracting DMPP quantitatively from soils a method connected to a HPLC analytic has been developed by us and was standardized in laboratory experiment with a silt clay field soil (allochtone Vega). The method is detailed described here. Its reliability has been tested in a 3 years field trial under varying cropping systems and climatic conditions asides the influence of DMPP on CO 2 −, CH 4 − and N 2 O- emissions, measured by the closed chamber method. Parallel a nitrifying bacterial consortium of the silty clay field soil was enriched and subjected to 0, the recommended DMPP concentration for field applications and a 10 times higher one. In incubation experiments the conversion of ammonium to nitrite and nitrate in presence and absence of DMPP was spectrophotometer determined and pH-shifts with a scaled litmus paper. In sacrificed flasks at the end of incubation morphological changes of the bacteria involved were studied by transmission electron microscope (TEM). Results The ammonium, nitrite and nitrate determinations and the TEM pictures show that in presence of the field applied DMPP concentration the nitrifying activity returned around 30 days later than in the control and the cells were slightly enlarged. In presence of a 10 times higher DMPP concentration a recovery was prevented. DMPP prolongs, compared with dicyandiamide (DCD), the period of nitrifiers’ inhibition and reduced N 2 O− and CO 2 − the emissions (Weiske et al., Biol Fertil Soils 34:109–117, 2001a , Nutr Cycl Agroecosys 60:57–64, b ). Conclusions With the method developed by us the stability of DMPP in agricultural soils can be satisfyingly and reproducible studied down to a detection limit of 0.01 μg DMPP g −1 dry soil. The morphological changes in the nitrifying consortium due to DMPP concentrations are in agreement with the recovery rate found by nitrite and nitrate formation.

Description: Background and aims Adequate zinc (Zn) in maize ( Zea mays L.) is required for obtaining Zn-enriched grain and optimum yield. This study investigated the impact of varying Zn fertilizer placements on Zn accumulation in maize plant. Methods Two pot experiments with same design were conducted to investigate the effect of soil Zn heterogeneity by mixing ZnSO 4 ·7H 2 O (10 mg Zn kg −1 soil on an average) in 10–15, 0–15, 25–30, 0–30, 30–60 and 0–60 cm soil layers on maize root growth and shoot Zn content at flowering stage in experiment-1, and assessing effects on grain Zn accumulation at mature stage in experiment-2. Results In experiment-1, Zn placements created a large variation in soil DTPA-Zn concentration (0.3–29.0 mg kg −1 ), which induced a systemic and positive response of root growth within soil layers of 0–30 cm; and shoot Zn content was increased by 102 %–305 % depending on Zn placements. Supply capacity of Zn in soil, defined as sum of product of soil DTPA-Zn concentration and root surface area at different soil layers, was most related to shoot Zn content ( r  = 0.82, P  〈 0.001) via direct and indirect effects according to path analysis. In experiment-2, Zn placements increased grain Zn concentration by up to 51 %, but significantly reduced the grain Zn harvest index from 50 % by control to about 30 % in average. Conclusion Matching the distribution of soil applied Zn with root by Zn placement was helpful to maximize shoot Zn content and grain Zn concentration in maize.

Description: Background and Aims Wetting-drying cycles are important environmental processes known to enhance aggregation. However, very little attention has been given to drying as a process that transports mucilage to inter-particle contacts where it is deposited and serves as binding glue. The objective of this study was to formulate and test conceptual and mathematical models that describe the role of drying in soil aggregation through transportation and deposition of binding agents. Methods We used an ESEM to visualize aggregate formation of pair of glass beads. To test our model, we subjected three different sizes of sand to multiple wetting-drying cycles of PGA solution as a mimic of root exudates to form artificial aggregates. Water stable aggregate was determined using wet sieving apparatus. Results A model to predict aggregate stability in presence of organic matter was developed, where aggregate stability depends on soil texture as well as the strength, density and mass fraction of organic matter, which was confirmed experimentally. The ESEM images emphasize the role of wetting-drying cycles on soil aggregate formation. Conclusions Our experimental results confirmed the mathematical model predictions as well as the ESEM images on the role of drying in soil aggregation as an agent for transport and deposition of binding agents.

Description: Background and aims Many plant growth-promoting endophytes (PGPE) possessing 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity can reduce the level of stress ethylene and assist their host plants cope with various biotic and abiotic stresses. However, information about the endophytic bacteria colonizing in the coastal halophytes is still very scarce. This study aims at isolating efficient ACC deaminase-producing plant growth-promoting (PGP) bacterial strains from the inner tissues of a traditional Chinese folk medicine Limonium sinense (Girard) Kuntze, a halophyte which has high economic and medicinal values grown in the coastal saline soils. Their PGP activity and effects on host seed germination and seedling growth under salinity stress were also evaluated. Methods A total of 126 isolates were obtained from the surface sterilized roots, stems and leaves of L. sinense (Girard) Kuntze. They were initially selected for their ability to produce ACC deaminase as well as other PGP properties such as production of indole-3-acetic acid (IAA), N 2 -fixation, and phosphate-solubilizing activities and subsequently identified by the 16S rRNA gene sequencing. For selected strains, seed germination, seedling growth, and flavonoids production in axenically growth L. sinense (Girard) Kuntze seedlings at different NaCl concentrations (0–500 mM) were quantified. Results Thirteen isolates possessing ACC deaminase activity were obtained. The 16S rRNA gene sequencing analysis showed them to belong to eight genera: Bacillus , Pseudomonas , Klebsiella , Serratia , Arthrobacter , Streptomyces , Isoptericola , and Microbacterium . Inoculation with four of the selected ACC deaminase-producing strains not only stimulated the growth of the host plant but also influenced the flavonoids accumulation. All four strains could colonize and can be re-isolated from the host plant interior tissues. Conclusions These results demonstrate that ACC deaminase-producing habitat-adapted symbiotic bacteria isolated from halophyte could enhance plant growth under saline stress conditions and the PGPE strains could be appropriate as bioinoculants to enhance soil fertility and protect the plants against salt stress.

Description: Aims The objective of this study was to investigate the effects of future warming and drought on (1) the biochemical composition of above-ground biomass of forage plants ( Festuca arundinacea and Dactylis glomerata ), (2) the potential mineralization of this material in soil, and (3) its priming effect on native soil organic matter. Methods We sampled above-ground plant material from spring regrowth and summer regrowth of a climate change experiment. While in spring, the plants were well watered, the summer regrowth was exposed to drought and elevated temperature (+3 °C) by infrared heating of the canopy during 3 weeks. We assessed the elemental and isotopic composition, lignin and non-cellulosic carbohydrate content and composition of plant material grown under all three conditions. Its mineralization potential in soil and priming effects were evaluated during laboratory incubation. Results Warming had no significant effect on elemental and stable isotope composition of both plant materials. In contrast, it resulted in reduction of lignin content for both plant species and decrease of the lignin-to-N ratio for F. arundinacea and increased non-cellulosic carbohydrate content for D. glomerata . Summer regrowth was characterised by increase of δ 13 C values, which is consistent with variations in stomatal conductance due to water shortage. Moreover, summer drought induced an increase in N content leading to decrease of the C/N ratio and increase of lignin-to-N ratio of summer regrowth compared to spring regrowth. Differences in decomposition were small, while priming effects were more strongly altered by the different exposure to enviromental. Conclusion Our results provide direct experimental evidence that extreme climatic events (high temperature and precipitation deficit) have an influence on soil carbon storage particularly through their effect on priming of native soil organic matter induced by altered plant litter. These effects seem to be governed by alterations of stoichiometry and to a smaller extent by alterations of plant chemical composition.

Description: A 26 years old agroforestry plantation consisting of four multipurpose tree species (MPTs) ( Michelia oblonga Wall, Parkia roxburghii G. Don, Alnus nepalensis D. Don, and Pinus kesiya Royle ex-Gordon) maintained at ICAR Research Complex, Umiam, Meghalaya, India were compared with a control plot (without tree plantation) for soil fertility status and CO 2 efflux. The presence of trees improved all the physico-chemical and microbial biomass parameters studied in this experiment. Relative to control, soils under MPTs showed significant increases of 17 % soil organic carbon, 26 % available nitrogen (AN), 28 % phosphorus (AP), 50 % potassium (AK), 65 % mean weight diameter (MWD) of aggregates, 21 % moisture and 34 % soil microbial biomass carbon (MBC) while reducing the mean bulk density (7 %). However, these parameters significantly differed among the tree species i.e., soils under A. nepalensis and M. oblonga had higher values of these attributes except bulk density, than under other species. Irrespective of treatments, the values of all these attributes were higher in surface soils while bulk density was highest in subsurface (60–75 cm). Cumulative CO 2 efflux under MPTs was significantly higher (15 %) and ranged from 1.71 g 100 g −1 ( M. oblonga ) to 2.01 g 100 g −1 ( A. nepalensis ) compared to control at 150 days of incubation. In all the treatments, increment in temperature increased the oxidation of soil organic matter, thereby increased the cumulative CO 2 efflux from soils. Of the tree species, with increment in temperature, A. nepalensis recorded more CO 2 efflux (2.50 g 100 g −1 ) than other MPTs but the per cent increase was more in control plot. P. kesiya and A. nepalensis recorded highest activation energy (59.1 and 39 kJ mol −1 , respectively). Net organic carbon sequestered in soil was highest under A. nepalensis (25.7 g kg −1 ) followed by M. oblonga (19.3 g kg −1 ), whereas control showed the lowest values. Amount of net carbon stored in the soil had significant and positive correlation with MBC ( r  = 0.706**), MWD ( r  = 0.636*), and AN ( r  = 0.825**).

Description: Background and aim Saccharothrix algeriensis NRRL B-24137, isolated from a Saharan soil, has been described as a potential biocontrol agent against Botrytis cinerea and other phytopathogens. However, the plant protection mechanisms involved still need to be described. The aim of this study was to determine this protection phenomenon as well as parts of the mechanisms involved, using Arabidopsis thaliana seedlings and B. cinerea . Methods The bacterial colonization process was evaluated on A. thaliana seedlings using fluorescence in situ hybridization. Protection of A. thaliana seedlings inoculated with NRRL B-24137 against B. cinerea was then evaluated. Parts of the mechanisms involved in the systemic protection against B. cinerea were evaluated using known mutants of genes involved in jasmonate (JA)/ethylene (ET)/salicylic acid (SA) signaling. Other Arabidopsis mutants, AtrhbohD-3 , AtrhbohF-3 , and ups1-1 were also screened to determine other parts of the mechanisms involved. Results The results showed that the strain NRRL B-24137 colonized, epi- and endophytically, the roots of Arabidopsis seedlings but the strain was not a systemic colonizer during the time of the experiment. The strain NRRL B-24137 also reduced B. cinerea symptoms and the protection was linked to known mechanisms of induced systemic resistance (ISR; JA/ET signaling), as well as to functionality of AtrbohF oxidase and of UPS1. Crosstalk between ET/JA and SA signaling could also be involved. Conclusions The isolate NRRL B-24137, after colonizing the root systems of A. thaliana , induces an ISR against B. cinerea , which is JA/ET dependent, but could also require SA crosstalk and protection could also require NAPDH oxidases and UPS1 functionalities.

Description: Agroforestry practices, such as Shaded Coffee and Homegardens, may provide habitat for forest butterflies and contribute to their conservation in fragmented agricultural landscapes. To determine the influence of agroforestry practices in an agricultural mosaic, the distribution of fruit-feeding butterflies was studied using a systematic approach that compared butterfly species richness in six land-use practices (Eucalyptus [ Eucalyptus spp.], Shaded Coffee, Homegardens, Secondary Growth, Pastures, and monocultures of Cassava [ Manihot esculenta ] and Sugarcane [ Saccharum officinarum ]), and in natural habitat (secondary Forest Edge and Interior) in two study areas (agricultural landscapes). In each study area, Van Someren-Rydon butterfly traps were placed as a grid every 150 m, creating quadrants of 2.2 and 2.4 km 2 that encompassed the different land-use practices. Land-use, plot area, number of traps and distance to the forest were set as covariates to compare species richness values. Butterfly species composition was compared using linear discriminant analysis (LDA). With the exception of Pastures, Cassava and Sugarcane, significant differences were not identified between the rest of the agricultural land-use practices and the forest habitats (edge and interior). The species composition in the agricultural practices was however, different to that found in forest habitats. Overall, Shaded Coffee practices that represent long-term mixed tree and crop stands have a better potential of conserving forest butterfly species compared to monoculture practices.

Description: Background and aims The effect of forest cover distribution and plant litter input on soil organic carbon were analyzed to better understand the dynamics of carbon cycling across ecosystems on the “Natural Oriented Reserve Bosco delle Pianelle”. Fluorescence spectroscopy represents a very useful tool to characterize soil organic matter properties, since it allows to directly monitor the molecular status of a fluorophore depending on its chemical environment, as well as on its structure, substituents of the aromatic moieties, and molecular weight. Here, fluorescence analysis was performed on humic acids isolated from four litters (HALs) and their underlying soils (HAs) at three depths. Methods All samples were collected from a protected forest area, Southern Italy, under different plant covering: Quercus ilex L. (Q), mixed Carpinus betulus L. and Carpinus orientalis Mill. (CC), Pinus halepensis L. (P), and mixed Quercus trojana Webb. and Quercus ilex L. (QQ). Results Data obtained showed a fast decomposition process for P and QQ litters, with HAs in the underlying soils characterized by the presence of simple, highly fluorescent structural components also in the deepest layers. On the contrary, a slow decomposition process was observed for Q and CC litters, whose underlying soil HAs were characterized by an increasing aromatic polycondensation and humification degree from the surface to the deepest layers, as supported by low values of fluorescence intensity and high wavelength maxima. Conclusions Results obtained indicate that P and QQ species promote C accumulation and stock in the underlying soils, thanks to a greater decomposition of their litter, and fluorescence spectroscopy is a very simple and suitable method to evaluate the influence of three species distribution on soil organic carbon pools.

Description: The Piaroa is an indigenous community located in the Venezuelan and Columbian Orinoquia. This community has made shifting agriculture part of their agricultural production system. This activity has allowed them to maintain food sovereignty and has guaranteed their territorial sustainability. The globalization processes and demographic growth however, have caused indigenous communities in the Venezuelan Orinoquia, including the Piaroa, to experience significant changes over the last four decades. These changes are characterized by the application of external development models and the consequent productive dependency. These factors threaten the continuity of the existing system. Our current understanding and administration of Piaroan agroforestry is composed of information designed to provide technical tools for generating sustainable management strategies for the tropical forests. Several anthropological and ecological studies have described the Piaroa shifting agricultural system for the purpose of providing aid. These studies also propose possible microsites selected by Piaroa farmers; however, the selection has not yet been investigated concretely. This information gives important contributing guidelines for agroforestry management and the selection of species in the Amazon, while taking into consideration shifting agriculture understanding. For this reason the temporary variability of the soil characteristics and their relationship with the spatial distribution of the crops is important. In the Cuao River watershed, located in the Venezuelan Amazon, ten systems of Piaroa shifting agriculture were randomly selected from different developmental stages. Established within these systems were a total of ten circular areas, each with a four-meter radius. In each of these areas the following was performed: (i) soil sample from the horizontal Ap (15 cm depth), (ii) vegetation inventory and (iii) an estimated area of the soil covered by biodegrading woody biomass, leaf litter cover and total vegetation cover. The temporary variability was determined by applying statistical methods to the information taken from the sites, according to the soil characteristics and properties. In the same way, a linear regression model was applied to explain the distribution of the cultivated species based on the soil’s properties and characteristics. The results indicate significant changes in Ca 2+ and K + throughout the sequence. Variations in the CO, N and P totals were also observed, however these attributes did not show significant differences. During the first part of the sequence (0–4 years), the applied models explained the cultivated species distribution, Manihot esculenta , Zea mays , Ananas comosus and Pouteria caimito , with R 2 〉0.5 and in a later stage (4–6 years) the model explained the distribution of fruit trees such as Theobroma grandiflorum and Pourouma cecropiifolia . Finally, in the most recent studies the model fails to explain the distribution of the species with noted exceptions such as Euterpe oleracea .

Description: Tropical forests store a large part of the terrestrial carbon and play a key role in the global carbon (C) cycle. In parts of Southeast Asia, conversion of natural forest to cacao agroforestry systems is an important driver of deforestation, resulting in C losses from biomass and soil to the atmosphere. This case study from Sulawesi, Indonesia, compares natural forest with nearby shaded cacao agroforests for all major above and belowground biomass C pools ( n  = 6 plots) and net primary production ( n  = 3 plots). Total biomass (above- and belowground to 250 cm soil depth) in the forest (approx. 150 Mg C ha −1 ) was more than eight times higher than in the agroforest (19 Mg C ha −1 ). Total net primary production (NPP, above- and belowground) was larger in the forest than in the agroforest (approx. 29 vs. 20 Mg dry matter (DM) ha −1  year −1 ), while wood increment was twice as high in the forest (approx. 6 vs. 3 Mg DM ha −1  year −1 ). The SOC pools to 250 cm depth amounted to 134 and 78 Mg C ha −1 in the forest and agroforest stands, respectively. Replacement of tropical moist forest by cacao agroforest reduces the biomass C pool by approximately 130 Mg C ha −1 ; another 50 Mg C ha −1 may be released from the soil. Further, the replacement of forest by cacao agroforest also results in a 70–80 % decrease of the annual C sequestration potential due to a significantly smaller stem increment.

Description: Aims The objective of our study was to confirm if hydraulic lift (HL) promotes nutrient uptake in field-grown plants in the same way as demonstrated previously in pot-grown plants. Methods We conducted a field experiment in an agroforestry system, over an entire growing season that included a dry period and a wet period. We used a shallow-root crop plant, mung bean ( Vigna radiata L.), intercropped with walnut ( Juglans regia L.) and jujube ( Zizyphus jujube Mill.), as an indicator for the presence of HL and its effects on nutrient uptake. To monitor HL, we artificially applied deuterium isotope to the deep roots of trees. Results We demonstrated the presence of a natural nitrogen, phosphorus, and potassium gradient along the soil depth, and the occurrence of HL, evidenced by deuterium signature in the shallow soil layers and V. radiata stem, only during the dry season. J. regia and Z. jujube both had deep root systems, but the former species exhibited stronger HL to the shallow soil than the latter. Meanwhile, the upper soil layers of J. regia had significantly higher moisture content, and the intercropped V. radiata had higher nutrient content. Conclusion HL can facilitate water uptake by V. radiata from the upper soil layers in the field condition during the dry season, which relates to nutrient acquisition by the crop.

Description: Aims and background Despite increasing knowledge of the role of allelochemicals in the productivity decline of replanted Chinese fir plantations, relatively little is known about the levels and sources of allelochemicals in relation to autoinhibition. Methods Allelopathic potential of litter, root exudates, and soils in successive rotations of Chinese fir plantations were detected. An allelochemical cyclic dipeptide (6-hydroxy-1,3-dimethyl-8-nonadecyl-[1,4]-diazocane-2,5-dione) from litter, root exudates, and soils in successive rotations was quantified. Results Extracts of leaf litter, fine root, and root exudates significantly inhibited the growth of Chinese fir germinants, and inhibition increased with successive rotations. Similar results were observed in the rhizosphere soil, basal soil, and bulk soil. The largest observed inhibition occurred in the rhizosphere soil. Furthermore, cyclic dipeptide was found in litter, root exudates, and soils, and the concentrations increased with successive rotations. The rhizosphere soil had the highest cyclic dipeptide level, followed by basal soil, while bulk soil contained the lowest concentration. There was a significant positive relationship between the inhibition of radicle growth of Chinese fir germinants and the concentration of cyclic dipeptide. Annual release of cyclic dipeptide through root exudation was 2.08–9.78 mol ha −1 annum, but the annual release of cyclic dipeptide through leaf litter decomposition was lowered to 0.32–1.41 mol ha −1 annum. Conclusions Cyclic dipeptide which caused autoinhibition of Chinese fir may be released into the soil through litter decomposition and root exudation. Root exudates provided more contributions to soil cyclic dipeptide levels than litter in Chinese fir plantations.

Description: Background and aims In the Central Negev hills (Israel) many ancient terraced wadis exist, which captured run-off and caused gradual soil aggradation, which enabled agricultural practices. In these terraces, dark colored soil horizons were observed, containing charcoal, as can be found in Terra Preta soils, suggesting higher fertility compared to natural soils. The aim of our investigation was to investigate these anthropogenic soils and to study the effects of charcoal and ash addition on soil properties and crop growth. Methods We investigated 12 soil profiles, focusing on possible differences between light and dark colored soil horizons. We also investigated the effects of amendment of charcoal and ash on the growth of wheat ( Triticum Aestivum L. ) in a 40-day pot experiment involving two water regimes. Results Results show that charcoal content in light and dark horizons were both low (〈0.2 %), but significantly lower bulk densities were found in dark colored horizons. In the crop experiment, charcoal addition resulted in decreased crop growth, while, in the water deficit regime, ash addition resulted in increased crop growth. Conclusions Considering the observed charcoal and the results from the crop experiment, we hypothesize that, in ancient run-off capturing agricultural systems, ash was purposefully added as fertilizer.

Description: The coffee leaf-miner (CLM) ( Leucoptera coffeella Guérin-Mèneville; Lepidoptera: Lyonetiidae), the main pest of coffee plants, occurs widely throughout the Neotropics where it has a significant, negative economic and quantitative impact on coffee production. This study was conducted in a rubber tree/coffee plant interface that was influenced by the trees to a varying degrees depending on the location of the coffee plants, i.e. from beneath the rubber trees, extending through a range of distances from the edge of the tree plantation to end in a coffee monocrop field. The most severe damage inflicted on coffee plants by the CLM (number of mined leaves) from April, which marks the start of the water deficit period, until September 2003 was in the zone close to the rubber trees, whereas the damage inflicted on plants in the monocropped field was comparable to that on coffee plants grown directly beneath the rubber trees, which received about 25–40 % of the available irradiance (I r —available irradiation at a certain position divided by the irradiation received in full sunlight, i.e. in the monocrop). From May until July damage caused by the CLM nearly doubled in each month. In midwinter (July), the damage decreased perceptibly from the tree edge toward the open field. From September onward, with the rising air temperatures CLM damage in the coffee monocrop started to increase. Based on these results, we conclude that coffee plants grown in the full sun incurred the most damage only at the end of winter, with warming air temperatures. Coffee plants grown in shadier locations (25–40 % I r ) were less damaged by the CLM, although a higher proportion of their leaves were mined. The rubber trees probably acted as a shelter during the cold autumn and winter seasons, leading to greater CLM damage over a distance outside the rubber tree plantation that was about equal to the height of the trees. Future studies should attempt to relate leaf hydric potential to pest attack in field conditions. More rigorous measurements of shade conditions could improve our understanding of the relationship of this factor to CLM attack.

Description: Non-timber forest products (NTFPs) are of high socio-economic value for rural people in West Africa. Main factors determining the status of the populations of socio-economically important tree species providing those NTFPs are human activities. This study assesses the impact of human population density, land use, and NTFP-harvesting (pruning and debarking) on population structure and fruit production of the socio-economically important tree Lannea microcarpa that is normally conserved by farmers on fields. We compared L. microcarpa stands of protected sites with those of their surrounding communal sites in two differently populated areas in Burkina Faso. Our results reveal an opposed land use impact on the population structure of L. microcarpa in the two areas. In the highly populated area, the species population was more stable in the protected site than in the communal site, while the opposite was observed for the less populated area. Trees of the communal sites bore more fruits than trees of the protected sites. Debarking and pruning had a negative impact on fruit production of the species. We conclude that low intensity of human impact is beneficial for the species and that indirect human impact facilitates fruit production of L. microcarpa . In contrast, in the densely populated area, human impact has reached an intensity that negatively affects the populations of L. microcarpa . While the extent of protecting L. microcarpa on fields still seems to be enough to guarantee the persistence of this important species in the less populated area, it is no longer sufficient in the densely populated area.

Description: Introduction In a recent paper, Warren et al. ( 2013 ) illustrated the potential of neutron radiography to visualize water dynamics in soil and plants. Methods After injection of deuterated water (D 2 O) in soil, the authors could monitor the changes of D 2 O concentration in roots. Results Based on the radiographs, the authors concluded that D 2 O was transported from roots growing in a wet soil region to roots in a dry region, proving hydraulic redistribution between roots. However, this interpretation depends on the correct estimation of D 2 O concentration in soil. Conclusions The experiments of Warren et al. ( 2013 ) could also be explained by diffusion of D 2 O from soil to roots, without hydraulic redistribution within the root system.

Description: Aims The mechanisms of belowground competition are not well understood. Addressing literature reports on competition-induced changes in tree fine root morphology, we conducted a growth experiment with tree saplings to investigate competition effects on important root morphological and functional traits in a root order-focused analysis. Methods European beech and European ash saplings were grown for 34 months in containers under greenhouse conditions in monoculture (2 conspecific plants), in mixture (1 beech and 1 ash) or as single plants. The root system was fractionated according to root orders and eight morphological and functional properties were determined. Results Root order was the most influential factor affecting the fine root traits (except for root diameter and δ 13 C); a significant species identity effect was found for root diameter, tissue density, N concentration and δ 13 C. Ash fine roots were thicker, but had lower tissue densities, contained more N and had systematically higher δ 13 C values than beech roots. The competition treatments had no significant effect on morphological root traits but altered δ 13 C in the 2nd root order. Conclusion Neither intra- nor interspecific root competition affected fine root morphology significantly suggesting that competition-induced root modification may not be a universal phenomenon in temperate trees.

Description: Background and aims Distinct metal distribution patterns within leaves of metal hyperaccumulating plants are repeatedly observed however, the presumable role of key structural biochemical molecules in determining and regulating their allocation remains largely unknown. We aimed to characterise in a spatially resolved manner the distribution of the main biochemical components in leaves of field-collected Cd/Zn-hyperaccumulating Noccaea praecox in order to relate them to metal distribution patterns at tissue level. Methods The biomolecular composition of the leaves was spatially analysed using synchrotron radiation Fourier Transform Infrared (FTIR) and the distribution of Zn with synchrotron radiation Low-Energy X-Ray Fluorescence (LEXRF) microspectroscopy was determined on the same tissues of interest (epidermis, sub-epidermis, mesophyll). Results In epidermal cells high proportion of free-carboxyl, nitro and phosphate groups standing for pectin, nitroaromatics, phytic and other organic acids were found. Adjacent mesophyll cells had higher proportions of proteins, carbohydrates and cellulosic compounds. Conclusions Pectin compounds were indicated as important components of Zn enriched epidermal cell walls. In addition, intense lignification of epidermal cell walls might limit leakage of the trapped metals back to the metabolically active and thus more sensitive mesophyll. Distribution of metal-binding compounds in particular cell types/tissues may therefore predispose metal distribution patterns and tolerance in leaves.

Description: Currently, the one of great threats to tropical biodiversity is the conversion of natural ecosystems to agriculture, and this threat is particularly critical on Hainan, the largest tropical island in China and a global biodiversity hotspot. Rubber ( Hevea brasiliensis ) has been planted on Hainan since the 1950s, resulting in extensive replacement of native forest, and the rate of this transformation has increased with latex prices since the 1990s. Rubber plantations now cover ca. 506,680 ha on Hainan and reach ca 1,000 m in elevation. To investigate the effect of this land-use change, we compared avian communities between a rubber plantation and a native secondary semi-deciduous monsoon forest. We found that species richness was higher in the native forest than in rubber, and that community composition differed greatly between the two habitats. No strict frugivores were recorded in rubber and no granivores in semi-deciduous monsoon forest. In both richness and abundance, more nectarivores and fewer insectivores occurred in rubber than in the native forest. Some common forest species, as well as protected species, were found only in native forest, including Hainan Partridge ( Arborophila ardens ), Red Junglefowl ( Gallus gallus ), Emerald Dove ( Chalcophaps indica ), Black-browed Barbet ( Megalaima oorti ), Blue-rumped Pitta ( Pitta soror ), Puff-throated Bulbul ( Alophoixus pallidus ), and Chestnut Bulbul ( Hemixos castanonotus ). Although ten babbler species were found in the native forest, only two were in rubber. Among the species missing in rubber was the endemic Hainan species Grey Laughingthrush ( Garrulax maesi ). Its endangerment through habitat conversion is of particular conservation concern.

Description: Aims Tree species affect herb layer species through their effects on soil quality and light regime but their relative importance and interactions are insufficiently known. Methods Pot experiment with soil taken from stands planted with tree species with contrasting effects on soil acidification, two light regimes and six forest perennials. Results The survival or growth of Mercurialis perennis, Lamium galeobdolon , Anemone nemorosa and Primula elatior was lower in the acid Alnus soils than in the less acid Fraxinus soils. By contrast, the acid tolerant Convallaria majalis and Dryopteris dilatata were barely affected by tree species. Light conditions had less impact than soil chemistry and did not compensate for unfavourable soil conditions. Ca and P concentrations increased in plants grown in Fraxinus soils. The Mg and Al shoot/root ratios of respectively one and two of the acid tolerant species was elevated in the most acid soil. Conclusions Tree species effects on forest perennials are mainly explained by increased Al concentrations under acidifying species. Changed plant concentrations and allocation are likely associated to Al antagonism. We found no light compensation for the soil effect on the studied species. However, light alters the plant nutrient concentrations and allocation which may suggest an indirect effect.

Description: Aims The aim of this study was to determine whether goat grazing in the understory of a pine forest at Doñana Natural Park could accelerate the decomposition of the pine needles accumulated on the soil surface and, if so, through which mechanisms. Specifically, the roles of trampling (mechanical fragmentation) and nutrient enrichment through defecation (fertilization) were evaluated in terms of their effect on pine needle decomposition rates. Methods An experiment was conducted featuring the following 4 treatments: 1) intact needles (control), 2) trampled needles, 3) intact needles fertilized with liquid manure, and 4) trampled needles fertilized with liquid manure. Litter decomposition was determined as a function of mass loss over time, using the litter-bag method. Bags were recovered 4, 8, 16, 24 and 36 months after burial in soil, dried and weighed. Needle length, leaf mass per area and C and N concentration were also measured in the buried litter-bags. Results Four months after burial, mass loss was greater in the trampled (23–27 %) than non-trampled (14–16 %) treatments. However, from 8 months onwards, decomposition rates in the fertilized treatments were significantly higher than those in the non-fertilized treatments (between 5 % and 15 % less mass loss). Meanwhile, fertilized treatments presented higher N content (2.1 %) than the non-fertilized ones (1.2 %), with a significantly lower C:N ratio also found in the in the fertilized treatment. Conclusions Trampling and fertilization during grazing accelerates litter decomposition and thus promotes the incorporation of N into the system. Acceleration of decomposition reduces the accumulation of pine needles on the soil surface, reducing the risk of fire.

Description: Background and aims Cadmium (Cd) could activate activity of mitogen-activated protein kinase MPK6 in plants. In this study, we investigated the role of MPK6 in mediating Cd toxicity in plants. Methods The wild type Arabidopsis plants (WT) and the mpk6 - 2 mutants were subjected either 0 (Control) or 10 μM Cd treatment. Kinase activity of MPK6, nitric oxide (NO) level, Cd concentration, and oxidative stress were measured. Results In WT plants, Cd exposure rapidly stimulated kinase activity of MPK6. However, upon Cd exposure, mpk6 - 2 showed better growth than the WT. Although Cd-induced production of NO in roots was greater in WT than in mpk6 - 2 , there was no difference in Cd concentration between the two plants. Nevertheless, the Cd-induced hydroperoxide burst, lipid peroxidation and loss of membrane integrity, were all more severe in the WT than in mpk6 - 2 . Foliar applications of antioxidant ascorbic acid, vigorously improved the growth of both the WT and mpk6 - 2 under Cd exposure. Thereby the growth difference between these two plants was minimized. Conclusions Mutation of mpk6 enhances Cd tolerance in plants by alleviating oxidative stress, but did not affect cadmium accumulation in plants.

Description: Background and Aims The role and linkage of endophytic bacteria to resistance of peanut seeds to biotic stress is poorly understood. The aims of the present study were to survey the experimental (axenic) and control (conventional) peanut plants for the predominant endophytic bacteria, and to characterize isolates with activity against selected A. flavus strains. Methods Young axenic plants were grown from presumably bacteria-free embryos in the lab, and then they were grown in a field. Endophytic bacterial species were identified by the analysis of DNA sequences of their 16S-ribosomal RNA gene. DNA extracted from soil was also analyzed for predominant bacteria. Results Mature seeds from the experimental and control plants contained several species of nonpathogenic endophytic bacteria. Among the eight bacterial species isolated from seeds, and DNA sequences detected in soil, Bacillus thuringiensis was dominant. All B. amyloliquefaciens isolates, the second abundant species in seeds demonstrated activity against A. flavus . This effect was not observed with any other bacterial isolates. There was no significant difference in number and relative occurrence of the two major bacterial species between the experimental and conventionally grown control seeds. Conclusion Endophytic bacterial colonization derives from local soil and not from the seed source, and the peanut plant accommodates only selected species of bacteria from diverse soil populations. Some bacterial isolates showed antibiosis against A. flavus.

Description: Background and Aims Climate warming and increased atmospheric nitrogen (N) deposition both have the potential to increase plant productivity over the next century, yet they can also increase decomposition and respiration. Our aim was to examine the extent to which warming and N addition can, on balance, alter net ecosystem CO 2 exchange (NEE) in a grass-dominated system. Methods We measured NEE responses to warming and N addition over two growing seasons in a temperate old field using steady-state flow-through chambers, which allowed for the integrated measurement of respiration and photoassimilation effects on net CO 2 flux over diel periods. We also assessed the relationship between NEE and plant biomass responses to the warming and N treatments. Results In both years, our study system was a net source of carbon (C) during the snow-free season. N addition did not significantly affect diel NEE or dark respiration in either year, despite a doubling in aboveground plant biomass in response to N addition in the second year, and a corresponding increase in peak daily net CO 2 photoassimilation in N addition plots. The warming treatment also had no significant effect on NEE, although the flow-through chambers required warming to be temporarily halted during NEE measurements. Conclusions Overall, our results both highlight the potential divergence of plant and soil responses to N addition and demonstrate the capacity for a grass-dominated system to function as a net source of C in consecutive years.

Description: Background and aim Intuitively, access to water from the soil at key phenological stages is important for adaptation to drought. This study aimed to assess the temporal pattern of water extraction under terminal drought stress. Methods Pearl millet genotypes with varying levels of terminal drought tolerance were grown in a lysimetric system with a soil volume and plant spacing similar to field conditions. Water extraction was monitored until maturity under differing water regimes. Results The yield did not differ among genotypes under well-watered (WW) conditions, and the water extraction profile of WW plants was similar across all genotypes. In contrast, the yield of sensitive genotypes was 30–100 % lower than that of tolerant lines under water stress (WS). The total volumes of water extracted by tolerant and sensitive genotypes were similar under WS; however, tolerant genotypes extracted less water prior to anthesis, and more water after anthesis. Grain yield was positively related to the amount of water extracted during week three after panicle emergence. Increased water extraction after anthesis benefitted the tillers more than the main culm and was correlated with higher staygreen scores. Conclusion Increased water uptake after anthesis, which results from earlier water conservation during pre-anthesis, increases yield under terminal drought in pearl millet.

Description: Background and aims Efficient accumulation of arsenic (As) in rice ( Oryza sativa L.) poses a potential health risk to rice consumers. The aim of this study was to investigate the mechanisms of uptake, transport and distribution of inorganic arsenic (As i ) and dimethylarsinic acid (DMA) in rice plants. Methods Rice was exposed to As i (As(V)) and DMA in hydroponics. High-performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) and synchrotron X-ray fluorescence (SXRF) microprobe were used to determine As concentration and the in situ As distribution. Results DMA induced abnormal florets before flowering and caused a sharp decline in the seed setting rate after flowering compared to As i . Rice grains accumulated 2-fold higher DMA than As i . The distribution of As i concentration (root 〉 leaf 〉 husk 〉 caryopsis) in As(V) treatments was different from that of the DMA concentration (caryopsis 〉 husk 〉 root ≥ leaf) in DMA treatments. SXRF showed that As i mainly accumulated in the vascular trace of caryopsis with limited distribution to the endosperm, whereas DMA was observed in both tissues. Conclusions DMA tended to accumulate in caryopsis and induced higher toxicity to the reproductive tissues resulting in markedly reduced grain yield, whereas As i mainly remained in the vegetative tissues and had no significant effect on yield. DMA is more toxic than As i to the reproductive tissues when both of them are at similar concentrations in nutrient solution.

Description: Background and aims Variations in responses to soil N between a non-N-fixing shrub, Baccharis halimifolia L., and a N-fixing shrub, Morella cerifera (L.) Small, were tested over 12 weeks to determine whether N availability is the sole cause of persistent dominance of M. cerifera on barrier islands. Methods Plants were supplied increasing levels of soil N up to 200 mg kg −1 . Measurements included gas exchange and chlorophyll fluorescence parameters across treatments, species, and time. Tissues were analyzed for differences in biomass and nutrients. Results Baccharis halimifolia had reduced physiological responses across all treatment levels, but M. cerifera had comparatively few variations. Across all treatments B. halimifolia photosynthesis and stomatal conductance were reduced by 62 and 76 %, respectively,by week 12. Increasing foliar δ 15 N values across treatments for M. cerifera indicated a shift from utilizing fixed N to available soil N. Biomass was highest at 200 mg kg −1  N for both species. Baccharis halimifolia showed indications of stress response and resource limitation based on physiological responses, nutrient contents, and isotope effects. Conclusions Baccharis halimifolia showed signs of co-limitation of both N and P whereas M. cerifera was limited by neither, suggesting that dominance of M. cerifera is only partially explained by actinorhizal symbiosis and N availability.

Description: Background and Aims Soil mineralization, nitrification, and dynamic changes in abundance of ammonia-oxidizing bacteria (AOB) and archaea (AOA) were studied to validate our hypothesis that soil mineralization and nitrification decreased along the chronosequence of rice cultivation. Methods Paddy soils with a 300, 700 and 2000-year cultivation history (P300, P700 and P2000) were selected to study net mineralization and nitrification processes. Dynamic abundance of AOB and AOA was estimated by quantifying their respective amoA gene copies. Results The net mineralization rate was higher for P300 than P700 and P2000. Potential nitrification ( N p ) and average nitrification rates ( V a ) were similar for P300 and P700 soils, but the simulated potential nitrification rate ( V p ) and nitrification rate (k 1 ) was 72 % and 88 % higher for P300 than P700, respectively. V a was about 70 % lower than for P2000 than P300 and P700. AOB amoA gene copies were higher for P300 than P700 and P2000, whereas AOA abundance did not show significant differences. AOB abundance showed a positive response to NH 4 supply but AOA did not. Conclusions Both N mineralization and nitrification were depressed with increased cultivation time. Archaea responded to mineralization positively rather than nitrification, which suggested that readily mineralized organic matter may play an important role in AOA.

Description: Aims The current study aimed to assess the potential of peanut ( Arachis hypogaea L.) for bioenergy production via phytoextraction in cadmium (Cd) -contaminated soils and screen appropriate cultivars for this approach. Methods A life-cycle pot experiment was conducted to determine the biomass, seed yield, oil content and Cd accumulation of seven peanut cultivars under Cd concentration gradients of 0, 2, and 4 mg kg −1 . Results Peanut exhibits genotypic variations in Cd tolerance, seed production, oil content, and Cd accumulation. Exposure of plants to 2 and 4 mg kg −1 Cd did not inhibit shoot biomass, seed yield, and oil content for most of the cultivars tested. There are large amounts of Cd accumulated in the shoots. Although the seed Cd concentration of peanut was relatively high, the Cd concentration in seed oils was very low (0.04-0.08 mg kg −1 ). Among the cultivars, Qishan 208 showed significant Cd tolerance, high shoot biomass, high pod and seed yield, high seed oil content, considerable shoot Cd concentration, and the largest translocation factor and total Cd in shoots. Conclusions The cultivation of peanut in Cd-contaminated farmland was confirmed to be feasible for bioenergy production via phytoextraction, and Qishan 208 is a good candidate for this approach.

Description: Background and aims Sufficient soil phosphorus (P) is important for achieving optimal crop production, but excessive soil P levels may create a risk of P losses and associated eutrophication of surface waters. The aim of this study was to determine critical soil P levels for achieving optimal crop yields and minimal P losses in common soil types and dominant cropping systems in China. Methods Four long-term experiment sites were selected in China. The critical level of soil Olsen-P for crop yield was determined using the linear-plateau model. The relationships between the soil total P, Olsen-P and CaCl 2 -P were evaluated using two-segment linear model to determine the soil P fertility rate and leaching change-point. Results The critical levels of soil Olsen-P for optimal crop yield ranged from 10.9 mg kg −1 to 21.4 mg kg −1 , above which crop yield response less to the increasing of soil Olsen-P. The P leaching change-points of Olsen-P ranged from 39.9 mg kg −1 to 90.2 mg kg −1 , above which soil CaCl 2 -P greatly increasing with increasing soil Olsen-P. Similar change-point was found between soil total P and Olsen-P. Overall, the change-point ranged from 4.6 mg kg −1 to 71.8 mg kg −1 among all the four sites. These change-points were highly affected by crop specie, soil type, pH and soil organic matter content. Conclusions The three response curves could be used to access the soil Olsen-P status for crop yield, soil P fertility rate and soil P leaching risk for a sustainable soil P management in field.

Description: Background and aims Gaseous losses of ammonia (NH 3 ) have been observed in citrus orchards when urea is surface-applied to the soils, and this loss might significantly limit the effectiveness of the nitrogen (N) fertilizer. However, a portion of the volatilized NH 3 might be absorbed by the plants through the leaves. To quantify the contribution of the leaf absorption of 15 NH 3 , a study with sweet oranges was conducted in two field areas where trees were grown at standard (480 trees ha −1 ) and high densities (617 trees ha −1 ). Methods Plastic trays were filled with soil, covered with mown grass to simulate field management conditions, fertilized with 15 N labeled urea (12 atom % excess) and placed under each of three trees in the orchards. This experimental procedure prevented the uptake of N from the labeled urea by the roots. Two weeks after 15 N fertilization, the trays were removed from the field, and the soil was homogenized and sampled for chemical analyses. The citrus trees under which the trays were placed were destructively harvested, and the total N concentrations and 15 N/ 14 N ratios were determined. Results After urea application, the NH 3 losses peaked within three days and subsequently decreased to negligible amounts after 10 days. The total NH 3 losses accounted for 55–82 % of the applied N. Although the NH 3 absorption by the citrus leaves was proportional to the tree density in the field, only 3–7 % of the 15 NH 3 volatilized from the soil was recovered by the citrus trees, and the NH 3 absorption was also influenced by the proximity of citrus trees to the site of urea application and the leaf areas of the trees. Conclusions The citrus trees can absorb the NH 3 volatilized from urea, even though, the amount recovered by the trees is small and does not represent a significant proportion of total gaseous N losses, what demonstrates the importance of enhanced N use efficiency practices in field to reduce losses of NH 3 when urea is applied to soil surfaces.

Description: Background Rice can accumulate arsenic (As) to relatively high concentrations due to the general flooding practices in rice cultivation, and organic matter in the soil strongly affected As bioavailability to rice plants. The influence of organic matter input on the As transformation in paddy soil and As uptake into rice plants is an area that is rarely investigated. Methods Biogas slurry (BGS), a commonly used organic fertilizer, was applied to an As contaminated paddy soil, in order to investigate the influence of organic matter on As transformation in the paddy soil and As accumulation in rice plants. Results Application of BGS significantly increased the As accumulation in rice plants, especially for methylated As species. Results showed that the concentrations of dissolved organic carbon (DOC) and dissolved Fe(II) in the soil solution were significantly increased by the BGS addition into the paddy soil, and were significantly correlated to the As concentration in the soil solution ( P  〈 0.01). The increase of soil pH and the decrease of the soil redox potential (Eh) were observed as well. These alteration of soil characteristics elevated the As release from soil particles to the soil solution under the addition of BGS. The increased concentrations of dimethylarsinic acid (DMAs(V)) and monomethylarsonic acid (MMAs(V)) in the soil solution, and the volatilized As of trimethylarsine (TMAs) from the paddy soil, suggested that As methylation and volatilization in the soil were also enhanced by BGS addition. The concentrations of methylated As species in rice husks and grains were increased by 105.8–105.9 % and 99.7–112.2 %, respectively. Conclusion These results suggested that the use of organic fertilizer, such as BGS in As-contaminated paddy soil, can significantly alter the behavior of As in soil-rice system and enhance As accumulation in rice plants and should therefore be avoided.

Description: Increasing trend in the sole crops commercialization has questioned the sustainability of the traditional gum Arabic agroforestry ( Bush - fallow ) system in western Sudan. This shift in the farming system from a traditional sustainable system to more commercialized one has resulted in a drastic decline in soil fertility, decreased crop productivity and low gum Arabic production. Therefore, identification of alternative options and incentives are required to ameliorate the negative environmental effects of increasing commercialization trends. This paper takes this issue and empirically investigating the factors influencing the decision to adopt agroforestry using a binary probit model. The results show that farmers with less commercialization, access to credit, less fragmented land, more education, high gum Arabic gate price, located away from the markets, and with more years of experience in farming are more likely to practice the traditional gum Arabic agroforestry system. In contrast, the allocation of more working days for commercial sole crops production, more fragmented land, and higher commercialization index reduces the probability of gum Arabic agroforestry adoption. In conclusion, this dichotomy between sole crop commercialization and traditional gum agroforestry system may be solved through the encouragement of the adoption of the traditional intercropping system with gum tree ( Acacia senegal ). Production of gum tree ( Acacia senegal ) itself should be more commercialized and prioritized. Conservation programs should focus on more educated, experienced famers with less fragmentized land if the policy is to promote the sustainable farming system in the region to promote soil fertility and to improve the effect of sole crop commercialization on traditional gum Arabic agroforestry system.

Description: This study analyses the trade-off between bioenergy production and soil conservation through thinning operations in Norway spruce ( Picea abies L. Karst) plantations in Denmark. Thinning operations were evaluated under different regimes and intensities for a complete rotation period of sixty years and for different site qualities (site-classes I–VI). Applying a dynamic forest growth modeling tool, evolution of forest structure was predicted to observe the potentials for biomass production and inevitable soil degradation. Results showed thinning from below, with a higher utilization (maintenance of a minimum basal area of 25 m 2  ha −1 ) could produce more bioenergy. However, these operations require simultaneous severe forest soil degradation. Therefore, the optimum thinning for bioenergy production under preservation constraints was thinning from above with a lower intensity (maintenance of a minimum basal area of 45 m 2  ha −1 ). The ratio of bioenergy win (kWh) to soil-loss (m 3  ha −1 ) was calculated for this regime varying between 74,894 kWh m −3 in a high quality site (site-class I) and 6,516 kWh m −3 in a low quality site (site-class VI) with an average of 44,282 kWh m −3 . However, this could not always preserve the highest amount of growing stock essential for natural dynamics of forest ecosystem with an exception of the low quality sites (site-class VI). Thus, when aiming at bioenergy production through thinning operations, trade-offs with soil conservation and growing stock preservation should be regarded to prevent environmental degradation.

Description: In a Metasequoia glyptostroboides coastal forest shelterbelt near Shanghai, China, we studied relationships between stand structure and wind shelter effect. We located 16 plots at intervals of 500 m along the shelterbelt and characterized both horizontal and vertical structure of each plot. Wind speed was measured within each plot and at different distances windward and leeward. We found that wind shelter effects were closely related to stand structure of the studied M. glyptostroboides shelterbelt. Stands with high basal area but intermediate crown index and intermediate proportion of large trees (LT) produced the best shelter effects, with significantly longer shelter distance ( d 70, shelter distance which the wind speed U does not exceed 70 % of U 0 ) and slightly lower minimum relative wind speed ( U m /U 0 ). Simple structural indices that can be easily measured in the field were good predictors of the shelter effect. LT was the best predictor of d 70, while basal area at ground level was the best predictor of U m / U 0 . The relationships between stand structure and shelter effect provides a practical guideline to the design, construction and management of forest shelterbelts. In order to provide the best shelter effects, high basal area of 〉50 m 2  ha −1 at ground level or 〉33 m 2  ha −1 at breast height coupled with an intermediate LT value of about 60 % should be maintained for the studied M. glyptostroboides shelterbelt.

Description: Improving trees location under LiDAR-derived digital canopy height models (DCMs) is of great interest as discrepancies between both dataset influence the accuracy of the estimations of forest attributes. A method is proposed for the co-registration of LiDAR-derived DCMs with local field positional measurements under a dense tree canopy. This approach consists of two main stages: (1) the assessment of the match between the LiDAR-derived digital terrain model and topographic surveying measurements when shifting the coordinates around a measured position; and (2) a comparison between the field height of selected trees and the LiDAR-derived DCM. Satisfactory results were obtained from geo-referencing field data and LiDAR models for characterizing the forest structure in heterogeneous Pinus sylvestris stands. Closure error of topographic surveying was 17.7 cm, and GPS accuracy to 95 % probability was below 10 cm, thus considerably lower than the resolution of the LiDAR models (1 m-pixel). The best co-location for field trees and LiDAR models provided a coefficient of determination of 0.56 between field-measured tree heights and LiDAR-derived DCM values.

Description: Coffee, Coffea arabica L., which is native to Ethiopia, is the world’s most widely traded tropical agricultural commodity. While much is known about the productivity and management of coffee for coffee beans little attention has been given to the plants overall biomass production and carbon sequestration. The objective of this study was to develop and evaluate allometric equations for estimating the aboveground biomass of C. arabica plants growing in indigenous agroforestry system in the Rift Valley escarpment of south-eastern Ethiopia. Coffee plays an important role in providing income and in sustaining these productive systems. Biomass harvesting of 31 plants with 54 stems was carried out in a 40 km 2 area varying in elevation from 1,500 to 1,900 m. The stem accounted for most (56 %) of plant biomass, followed by branches (39 %) and twigs plus foliage (5 %). Plant mean biomass was 22.9 ± 15.8 kg. Power equations using stem diameter measured at either 40 cm ( d 40 ) or at breast height ( d , 1.3 m) with and without stem height ( h ) were evaluated. The square power equation, $ Y \; = \; b_{ 1} d_{ 40}^{ 2} $ , was found to be the best (highest ranked using goodness-of-fit statistics) for predicting total and component biomass. The reliability of the prediction decreased in the order: stem 〉 branches 〉 twigs plus foliage. A cross-validation procedure showed that equation parameterization was stable and coefficients reliable. Our parameterized square power equation for total aboveground biomass was also found to be better than the equations parameterized by Hairiah et al. (Carbon stocks of tropical land use systems as part of the global C balance: effects of forest conversion and options for clean development activities, International Centre for Research in Agroforestry, Bogor, 2001 ) and Segura et al. (Agroforest Syst 68:143–150, 2006 ) for C. arabica grown in agroforestry systems, confirming the importance of parameterization of allometric equations with site specific data when possible.

Description: Vegetative filter strips (VFS) have long been promoted as a soil conservation practice that yields many additional environmental benefits. Most previous studies have focused primarily on the role of vegetation and/or soil physical properties in these ecosystem services. Few studies have investigated the soil microbial community of VFS. Therefore, we examined potential differences in soil microbial community characteristics of claypan soil planted to VFS with differing vegetation and a traditional row-crop system in a maize–soybean rotation. Samples were tested for soil microbial function and community structure using dehydrogenase and fluorescein diacetate (FDA) hydrolysis enzyme assays and phospholipid fatty acid (PLFA) analysis, respectively. The grass VFS soil exhibited the greatest dehydrogenase activity levels and FDA activity was greater in the grass and agroforestry (i.e., tree–grass) VFS soils relative to the cropland soil. The PLFA analysis revealed community structural differences underlying these functional differences. The agroforestry VFS soil was characterized by a greater proportion of total bacteria, gram-negative bacteria, anaerobic bacteria and mycorrhizal fungi than the cropland soil. The grass VFS soil shared some characteristics with the cropland soils; but the grass VFS supported greater mycorrhizal fungi and protozoa populations. This work highlights differences in soil microbial function and community structure in VFS relative to cropland soil 12 years post VFS establishment. It also enhances our fundamental knowledge regarding soil microorganisms in VFS, which may aid in explaining some ecosystem services provided by VFS (e.g., decomposition of organic agrichemicals).

Description: Arbuscular mycorrhizal (AM) symbioses may alter the competitive abilities of plant species and facilitate positive interactions such as nutrient transfer between plants. They are therefore particularly interesting components in agroforestry systems. We studied spatial variation of AM colonisation on a cut-and-carry fodder production site (agroforestry plot) of the legume tree Gliricidia sepium and the fodder grass Dichanthium aristatum . Roots of the two plant species were sampled under the tree canopies and on the adjacent grass plot at 1 and 3.5 m from the first tree row where G. sepium roots also occur. Roots of D. aristatum were also sampled on a nearby grass monocrop. Colonisation of arbuscules, vesicles and hyphae in root samples was visually determined, and AM fungal species were identified by DNA sequencing. Colonisation and frequency of types of AM formations varied statistically significantly between the species and sampling points. Arbuscular colonisation in G. sepium roots was higher under the tree canopies than on the adjacent grass plot. Soil nutrient content, particularly P and N, and interspecies competition are the most probable explanations for the observed variation in AM colonisation. Both arbuscular colonisation and arbuscule:vesicle ratio in D. aristatum roots was lower on the D. aristatum monocrop than on the agroforestry plot under or near the tree canopies. Intercropping could stimulate AM symbiosis in D. aristatum . Both plant species formed symbiosis with Rhizophagus intraradices , indicating potential for interplant N transfer via common mycelial networks of AM-forming fungi.

Description: Light and soil moisture availability are two important abiotic factors influencing plant growth in an agroforestry system. Different soil moisture and light treatments were applied to examine the combined impact of drought and shade on the morphological plasticity of Vitex negundo var. heterophylla (Chinese chastetree) and Ziziphus jujuba var. spinosa (Spine jujube). We found that the interaction of light and soil moisture was orthogonal in the two species. V. negundo captured irradiance efficiently with relatively long petiole and petiolule, while Z. jujuba maintained higher branches to absorb light than V. negundo . Compared to the seedlings under full sunlight, the palmately compound leaves of V. negundo under low light showed larger specific leaf area (SLA), lower ratio of leaflet length to width and higher leaf mass ratio (leaf biomass to total biomass); in contrast, the simple leaves of Z. jujuba under low light showed larger SLA and ratio of leaf length to petiole length. In both species, drought reduced the branch number, mean internode length of stem, and increased root mass ratio (root biomass to total biomass), but leaf morphology showed little variation to the decreased soil moisture. Between the two species, V. negundo is more shade-tolerant, while Z. jujuba is more drought-tolerant. In an alley cropping system, the spacing can be smaller in the V. negundo -crop system than the Z. jujuba -crop system when soil moisture is adequate. However, the V. negundo -crop system should be managed with more caution under the soil moisture limited conditions.

Description: Agroforestry is a new name for a rather old practice. From a historical point of view, various agroforestry systems existed in Europe, of which the wood pastures (Neolithicum), the Dehesas in Spain (~4,500 years old) and the Hauberg of the Siegerland (established in the Middle Age) are the most prominent. Other widespread systems in Europe were hedgerows, windbreaks and Streuobst (orchard intercropping). Due to mechanisation and intensification of agriculture, trees have been progressively removed from agricultural fields and traditional agroforestry systems slowly disappeared. Today, agroforestry systems are again increasing in interest as they offer the potential to solve important ecological and, especially, biodiversity problems, while at the same time enabling the production of food, wood products and fodder for cattle. Although agroforestry systems offer many advantages, many farmers are sceptical of these systems and are critical and risk-averse with regard to adopting new practices. However, in comparison to traditional systems, modern agroforestry systems can be adapted to current farming practices. By selecting suitable trees and appropriate tree management, high-quality timber can be produced without influencing agricultural crops excessively. In future, agroforestry systems will become increasingly important as they offer the prospect of producing woody perennials for bioenergy on the same land area as food and/or fodder plants, while enhancing overall biodiversity.

Description: Interactions among ecosystem services are increasingly perceived as important to ecosystem service delivery. Synergies and trade-offs among ecosystem services arise through direct ecological interactions or indirectly through correlated responses to other factors. To investigate whether and how interactions of overstory trees and shrubs with livestock forage species growing beneath generate ecosystem service interactions, overstory and forage species were examined in smallholder fallows in western Kenya. In 18 grazed and 21 improved fallows, we estimated biomass and quantified soil properties. We assessed whether the overstory reduces forage biomass and quality through competition, and whether overstory niche complementarity ameliorates competition or enhances facilitation. In improved fallows, forage biomass declined with overstory biomass, indicating competition and a wood-forage trade-off. In grazed fallows, biomass of higher quality forage species increased with overstory biomass, indicating a synergy, likely indirect. Niche complementarity, quantified as taxonomic and functional diversity, did not appear influential. Forage quality was not associated with overstory characteristics, but declined with grazing intensity. The contrasting relationships between overstory and forage species among fallow types appear ultimately attributable to the presence and intensity of grazing and the dense overstory in improved fallows.

Description: Gum arabic production from Acacia senegal is lower in sub-humid areas than arid areas. Water stress is thought to be the reason for higher yields in arid areas. The application of ethephon is thought to mimic the effect of water stress in other plants. The objective of this study was to determine if the application of ethephon would increase the gum yields of Acacia senegal under sub-humid conditions in Cameroon. Trees receiving 40 or 120 mg ethephon were compared to controls in field experiments at a semi-arid and a sub-humid location in Northern Cameroon, over two seasons. Two provenances from drier areas (Sudan) were compared to the local one. In the first season, gum yield of the local provenance treated with ethephon was increased by 400–600 % compared to the untreated trees. Gum yield at the semi-arid location was 77, 313 and 214 g/tree with 0, 40 and 120 mg ethephon/tree, respectively, while at the sub-humid location, it was 30, 186 and 114 g/tree with 0, 40 and 120 mg ethephon/tree. However, in the second season, the effect of ethephon was not significant in the semi-arid area, whereas it was evident in the sub-humid area (up to 478 g/tree). Moreover, ethephon did not affect gum yield of provenances from drier areas (Sudan). This showed that the water-stress hypothesis has to be refined. The development of ethephon-based tapping systems is promising, but requires further studies with a wider range of environmental conditions and A. senegal provenances.

Description: Background & aims Plants may have dissimilar effects on ecosystem processes because they possess different attributes. Given increasing biodiversity losses, it is important to understand which plant traits are key drivers of ecosystem functions. To address this question, we studied the response of two ecosystem functions that remove nitrogen (N) from wetland soils, the accumulation of N in plant biomass and denitrification potential (DNP), to variation in plant trait composition. Methods Our experiment manipulated plant composition in a riparian wetland. We determined relative importance of plant traits and environmental variables as predictors of each ecosystem function. Results We demonstrate that Water Use Efficiency (WUE) had a strong negative effect on biomass N. Root porosity and belowground biomass were negatively correlated with DNP. Trait ordination indicated that WUE was largely orthogonal to traits that maximized DNP. Conclusions These results indicate that plant species with different trait values are required to maintain multiple ecosystem functions, and provide a more mechanistic, trait-based link between the recent findings that higher biodiversity is necessary for multi-functionality. While we selected plant traits based on ecological theory, several of the plant traits were not good predictors of each ecosystem function suggesting the ecological theory linking traits to function is incomplete and requires strengthening.

Description: Wild leek ( Allium tricoccum ) is an edible spring ephemeral of the eastern deciduous forests of North America that takes advantage of the short period of high light conditions between snowmelt and canopy closure to accumulate the carbon required to complete its annual growth and seed production. In Québec (Canada), this slow-growing species has been subjected to great harvesting pressure, which forced the provincial government to ban commercial harvest and sales in 1995. An illegal market has since developed and the plant is still under threat. Conservation of existing natural populations might be possible through commercial production of wild leek. To investigate this possibility, we set up plots in four sugar maple forest stands where different organic fertilizer and gypsum (0 or 3,000 kg ha −1 ) applications were tested, together with two wild leek varieties, and bulb planting season. The two varieties, tricoccum and burdickii , despite morphological differences, are both suitable for cultivation. Planting bulbs in the spring seems more advantageous than in autumn, but these results will need to be confirmed. Fertilized plants exhibited better growth the year following transplantation than did non-fertilized plants. Belowground:aboveground biomass ratios indicated that plants receiving more fertilizer produced larger bulbs, but leaf size did not differ statistically. According to leaf nutrient analysis, fertilizers would need to be applied each year, whereas gypsum (as a calcium source) can be applied less frequently. Our results indicated a high potential for wild leek as a forest crop, at least when the bulbs are planted.

Description: Aims Wild soybean accession PI 468917 [ Glycine soja (Sieb. and Zucc.)] was examined for traits that could potentially be beneficial for development of drought resistant soybean cultivars. Methods Water use was examined in controlled environment chambers at three temperatures (25, 30, and 35 °C). Root morphology of plants grown in hydroponics was analyzed using digital imaging software. Results Wild soybean had lower transpiration efficiency in producing mass than the domesticated soybean cultivar Hutcheson at all temperatures. As soil dried, wild soybean decreased transpiration earlier (at a higher soil water content) than domesticated soybean, but only at 25 °C. Wild soybean had much greater root length than the modern soybean when grown at 25 or 30 °C in hydroponics, with the increase observed in the 0.25 to 0.50 mm diameter class. Wild soybean’s advantages dissipated at higher growth temperatures. Conclusions Wild soybean populations, potentially, can offer useful traits for improving drought resistance of modern soybean. Sensitive transpiration control in response to soil drying would contribute to ‘slow-wilting’ strategies known to be advantageous for drought resistance, and greater root length would enhance water acquisition from the soil profile. Use of the traits in breeding programs will require extending the temperature range for trait expression.

Description: Aims Seed germination and seedling emergence are vulnerable to water stress in arid environments. When precipitation is low and unpredictable during the early growing season, seeds near the sand surface often suffer from hydration/dehydration during germination. We investigated the responses of seedling emergence and survival of a sand dune grass with high sand stabilization value to amount and frequency of precipitation and depth of burial in sand. Methods Effects of amount and frequency of precipitation, burial and hydration/dehydration on seedling emergence of Leymus secalinus , were examined using standard procedures. Results Seedling emergence was affected by amount and frequency of monthly precipitation and depth of burial, and it decreased as precipitation frequency decreased with same amount of precipitation. Highest emergence percentage was obtained with 100 or 150 mm precipitation at 1–4 cm depth. Hydration/dehydration treatments decreased germination and increased dormancy percentage. Young seedlings with root lengths of 0–1 mm desiccated up to 30 days revived after rehydration. Conclusions Seedling emergence of L. secalinus is adapted to 150 mm monthly precipitation with frequency of 10–30 times per month, 1–4 cm burial depth and dehydration interval of 1–2 days. Alteration of amount and/or frequency of precipitation caused by climate change could markedly affect seedling emergence and population regeneration of this species.

Description: Background and aims Limited information is available on comparing the iron plaque formation capabilities and their effect on arsenic (As) uptake by different rice plant genotypes grown in As-contaminated soils. This study investigates the effect of iron plaque on As uptake in different rice genotypes grown in As-contaminated soils from the Guandu Plain of northern Taiwan. Methods Twenty-eight rice genotypes including 14 japonica and 14 indica genotypes were used in this study. Rice seedlings were grown in As-contaminated soils for 38 days. The iron plaque formed on the rice roots were extracted using dithionite–citrate–bicarbonate. The concentrations of As, Fe, and P in soil solutions, iron plaque, and plants were measured. The speciation of As in the root’s iron plaque was determined by As K-edge X-ray absorption near-edge structure spectroscopy (XANES). Results The amounts of iron plaque formation on roots were significantly different among 28 tested rice genotypes, and 75.7–92.8 % of As uptake from soils could be sequestered in iron plaque. However, there were no significant negative correlations between the amounts of Fe or As in the iron plaque and the content of As accumulated in rice plants of tested genotypes. XANES data showed that arsenate was the predominant As species in iron plaque, and there were difference in the distribution of As species among different rice genotypes. Conclusions The iron plaque can sequester most of As uptake from soils no matter what rice genotypes used in this study. However, the iron plaque alone did not control the extent of As accumulation in rice plants from As-contaminated soils among 28 tested rice genotypes. Low As uptake genotypes of rice selected from this study can be recommended to be grown in the As-contaminated soils.

Description: Background and aims Freeze events can strongly influence many ecosystem processes. However, the effects of freeze events on litter production, litter quality, and decomposition are rarely documented. Methods In this study, litter fall was measured monthly for 2 years. Two litter decomposition experiments were also performed using freeze-damaged litter and non-damaged litter in a loblolly pine forest. Results The freeze event in November 2009 caused a pronounced pulse of needle litter fall. The freeze-damaged needle litter was shown to have higher N concentration and lower C/N ratio compared with the normal falling needle litter. This finding indicates that freeze damage significantly increased needle quality because of incomplete nutrient resorption. The decomposition of freeze-damaged needle litter was faster than that of normal falling yellow needle litter and slower than that of hand-picked green needle litter. The decomposition rate constant ( k ) was negatively correlated with the C/N ratio in the needle litter. Our results also showed that the different climatic conditions influence patterns of litter decomposition. Conclusions This study suggests that freeze events significantly alter litter quantity and quality, thus affecting litter decomposition rates in a loblolly pine forest in central China.

Description: Background and aims Serpentine soils impose limits on plant growth and survival and thus provide an ideal model for studying plant adaptation under environmental stress. Despite the increasing amount of data on serpentine ecotypic differentiation, no study has assessed the potential role of polyploidy. We tested for links between polyploidy and the response to serpentine stress in Knautia arvensis , a diploid-tetraploid, edaphically differentiated complex. Methods Variation in growth, biomass yield and tissue Mg and Ni accumulation in response to high Mg and Ni concentrations were experimentally tested using hydroponic cultivation of seedlings from eight populations of different ploidy and edaphic origin. Results Regardless of ploidy level, serpentine populations exhibited higher tolerance to both Mg and Ni stress than their non-serpentine counterparts, suggesting an adaptive character of these traits in K. arvensis . The effect of ploidy was rather weak and confined to a slightly better response of serpentine tetraploids to Mg stress and to higher biomass yields in tetraploids from both soil types. Conclusions The similar response of diploid and tetraploid serpentine populations to edaphic stress corresponded with their previously described genetic proximity. This suggests that serpentine tolerance might have been transmitted during the local autopolyploid origin of serpentine tetraploids.

Description: Background and Aims Seed bank persistence plays a highly relevant role for population dynamics. The impact of interacting environmental factors on seed longevity has only scarcely been investigated. We aimed to analyse the effects of varied soil substrate type and moisture on soil seed survival. Methods Seeds of three Rumex species native to different habitats were buried in pots placed in open-air basins. The factors substrate (sand, loam, mud), water table depth (WTD; high, intermediate, low), time, and their interactions were investigated. Viability was tested after 6, 12, and 18 months. Results Seeds of R. acetosella (dry habitat) were short-term persistent with highest survival in low WTD on sand. Survival in R. acetosa (moist habitat) was very strongly reduced after 6 months with highest survival under wet conditions. R. maritimus (wet habitat) had overall long-term seed survival, where ‘substrate type’ had the strongest impact. Significant interactions of ‘substrate type’ and WTD were detected. Conclusions Seed bank longevity is not a fixed species trait, but varies with environmental factors. Soil moisture, substrate type and their interactions have different effects on the studied species. Persistence-classifications ought to consider the impact of environmental factors.

Description: More than 300 wild edible mushrooms are consumed in Mexico. They have been reported mainly from temperate forests in the center and southeast of the country. However, these valuable non-timber forest products are under-utilized because a lack of knowledge on their ecology and productivity. The objectives of this work were to compare the richness and fruit body production of wild edible mushrooms in temperate forests with a distinct vegetation composition in Amanalco, to describe species availability, and to test a new sampling approach in a heterogeneous environmental context. We designed a sampling method with random transects rather than traditional fixed sampling sites. Our method permits the acquisition of data from the highest number of environmental conditions. In 2009 and 2010, we collected and counted mushrooms in 248 transects distributed in five vegetation types ( Abies , Abies – Pinus , Pinus , Pinus – Quercus and Quercus ). We calculated the ecological importance value of each species as a function of its relative abundance and relative spatial frequency and relative temporal frequency. Abies religiosa pure stands and A. religiosa – Pinus forests had the greatest richness of edible fungi (43.1 and 21.3 species ha −1 , respectively) and produced most of the fruit bodies (1,160 and 820 ha −1 , respectively). The most abundant species in Amanalco region (combining all the vegetation types), Clavulina cinerea , Clitocybe gibba and Russula brevipes , also had the highest ecological importance value (0.2312, 0.1709 and 0.1516, respectively). These temperate forests maintain a considerable diversity of valuable wild edible mushrooms that are heterogeneously distributed according to the type of vegetation.

Description: The shea tree, Vitellaria paradoxa , is one of the most economically and culturally important indigenous tree species in the Sudano-Sahelian region. Its seeds contain a vegetable fat, internationally known as shea butter, which is widely used in edible, cosmetic and pharmaceutical sectors. Based on samples from 456 trees distributed in 17 locations across the species natural range from Senegal to Uganda, the fatty acid and tocopherol variation, and its relationship with geographic and climatic variables, was assessed in order to address the pattern and the origin of this variation across the natural range. Significant differences between Western and Eastern regions for oleic, stearic acid, saturated–unsaturated acid ratio and γ-tocopherol were identified that it is postulated maybe a result of genetic drift due to the evolutionary history of shea tree populations. Within regions the difference among stands was significant for most constituents; however the major part of the variation was observed among trees within stand (53–90 %). Relationships with climatic variables were not verified, weakening evidence for clinal variation hypotheses suggested by previous studies.

Description: Intensification of coffee ( Coffea arabica ) production is associated with increases in inorganic fertilizer application and decreases in species diversity. Both the use of organic fertilizers and the incorporation of trees on farms can, in theory, reduce nutrient loss in comparison with intensified practices. To test this, we measured nutrient concentrations in leachate at 15 and 100 cm depths on working farms. We examined (1) organically managed coffee agroforests (38 kg N ha −1  year −1 ; n  = 4), (2) conventionally managed coffee agroforests (96 kg N ha −1  year −1 ; n  = 4), and (3) one conventionally managed monoculture coffee farm in Costa Rica (300 kg N ha −1  year −1 ). Concentrations of nitrate (NO 3 − -N) and phosphate (PO 4 3− -P) were higher in the monoculture compared to agroforests at both depths. Nitrate concentrations were higher in conventional than organic agroforests at 15 cm only. Soil solutions collected under nitrogen (N)-fixing Erythrina poeppigiana had elevated NO 3 − -N concentrations at 15 cm compared to Musa acuminata (banana) or Coffea . Total soil N and carbon (C) were also higher under Erythrina . This research shows that both fertilizer type and species affect concentrations of N and P in leachate in coffee agroecosystems.

Description: Background and aims Chelant-enhanced phytoextraction has given variable and often unexplained experimental results. This work was carried out to better understand the mechanisms of Cd plant uptake in the presence of EDTA and to evaluate the contributions of Cd-EDTA complexes to the uptake. Method A 1-D mechanistic model was implemented, which described the free Cd 2+ root absorption, the dissociation and the direct absorption of the Cd-EDTA complexes. It was used to explain Cd uptake by maize in hydroponics and in soil. Results In hydroponics, the addition of EDTA caused a decrease in Cd uptake by maize, particularly when the ratio of total EDTA ([EDTA] T ) to total Cd ([Cd] T ) was greater than 1. At [Cd] T = 1 μM, when [EDTA] T /[Cd] T 〈 1, the model indicated that Cd uptake was predominantly due to the absorption of free Cd 2+ , whose pool was replenished by the dissociation of Cd-EDTA. When [EDTA] T /[Cd] T 〉 1, the low Cd uptake was mostly due to Cd-EDTA absorption. In soil spiked with 5 mg Cd kg −1 , Cd uptake was not affected by the various EDTA additions, because of the buffering capacity of the soil solid phase. Conclusions Addition of EDTA to soil increases Cd solubility but dissociation of Cd-EDTA limits the availability of the free Cd 2+ at the root surface, which finally reduces the plant uptake of the metal.

Description: Background and aims The feather moss Pleurozium schreberi (Brid.) Mitt. is colonized by cyanobacteria, which fix substantial amounts of atmospheric nitrogen (N) in pristine and N-poor ecosystems. Cyanobacterial N 2 fixation is inhibited by N deposition. However, the threshold of N input that leads to the inhibition of N 2 fixation has not been adequately investigated. Further, the ability of N 2 fixation to recover in mosses from high N deposition areas has not been studied to date. Methods We conducted two laboratory studies in which we (1) applied a range of concentrations of N as NH 4 NO 3 to mosses from low N-deposition areas, and (2) we deprived mosses from a high N-deposition area of N to test their ability to recover N 2 fixation. Results Higher addition rates (up to 10 kg N ha −1 ) did not systematically inhibit N 2 fixation in P. schreberi . Conversely, upon weeks of N deprivation of mosses from a high N environment, N 2 fixation rates increased. Conclusions The threshold of total N deposition above which N 2 fixation in P. schreberi is inhibited is likely to be 〉 10 kg N ha −1 . Further, cyanobacteria are able to recover from high N inputs and are able to fix atmospheric N 2 after a period of N deprivation.

Description: Background and aims Soil aggregation is a crucial aspect of ecosystem functioning in terrestrial ecosystems. Arbuscular mycorrhizal fungi (AMF) play a key role in soil aggregate formation and stabilization. Here we quantitatively analyzed the importance of experimental settings as well as biotic and abiotic factors for the effectiveness of AMF to stabilize soil macroaggregates. Methods We gathered 35 studies on AMF and soil aggregation and tested 13 predictor variables for their relevance with a boosted regression tree analysis and performed a meta-analysis, fitting individual random effects models for each variable. Results and conclusions The overall mean effect of inoculation with AMF on soil aggregation was positive and predictor variable means were all in the range of beneficial effects. Pot studies and studies with sterilized sandy soil, near neutral soil pH, a pot size smaller than 2.5 kg and a duration between 2.2 and 5 months were more likely to result in stronger effects of AMF on soil aggregation than experiments in the field, with non-sterilized or fine textured soil or an acidic pH. This is the first study to quantitatively show that the effect of AMF inoculation on soil aggregation is positive and context dependent. Our findings can help to improve the use of this important ecosystem process, e.g. for inoculum application in restoration sites.

Description: Background and aims Emission of the greenhouse gas (GHG) nitrous oxide (N 2 O) are strongly affected by nitrogen (N) fertilizer application rates. However, the role of other nutrients through stoichiometric relations with N has hardly been studied. We tested whether phosphorus (P) availability affects N 2 O emission. We hypothesized that alleviation of plant P-limitation reduces N 2 O emission through lowering soil mineral N concentrations. Methods We tested our hypothesis in a pot experiment with maize ( Zea mays L.) growing on a P-limiting soil/sand mixture. Treatment factors included P and N fertilization and inoculation with Arbuscular Mycorrhizal Fungi (AMF; which can increase P uptake). Results Both N and P fertilization, as well as their interaction significantly ( P  〈 0.01) affected N 2 O emission. Highest N 2 O emissions (2.38 kg N 2 O-N ha −1 ) were measured at highest N application rates without P fertilization or AMF. At the highest N application rate, N 2 O fluxes were lowest (0.71 kg N 2 O-N ha −1 ) with both P fertilization and AMF. The N 2 O emission factors decreased with 50 % when P fertilization was applied. Conclusions Our results illustrate the importance of the judicious use of all nutrients to minimize N 2 O emission, and thereby further underline the intimate link between sound agronomic practice and prudent soil GHG management.

Description: Aims Integrating multiple soil and disease management practices may improve crop productivity and disease control, but potential interactions and limitations need to be determined. Methods Three different potential disease-suppressive management practices, including a Brassica napus (rapeseed) green manure rotation crop, conifer-based compost amendment, and three biological control organisms ( Trichoderma virens, Bacillus subtilis , and Rhizoctonia solani hypovirulent isolate Rhs1A1 ) were evaluated alone and in combination at sites with both organic and conventional management histories for their effects on soilborne diseases and tuber yield. Results Rapeseed rotation reduced all observed soilborne diseases (stem canker, black scurf, common scab, and silver scurf) by 10 to 52 % in at least one year at both sites. Compost amendment had variable effects on tuber diseases, but consistently increased yield (by 9 to 15 %) at both sites. Biocontrol effects on disease varied, though Rhs1A1 decreased black scurf at the conventional site and T. virens reduced multiple diseases at the organic site in at least one year. Combining rapeseed rotation with compost amendment both reduced disease and increased yield, whereas biocontrol additions produced only marginal additive effects. Conclusions Use of these treatments alone, and in combination, can be effective at reducing disease and increasing yield under both conventional and organic production practices.

Description: Aims This study investigated Cu uptake and accumulation as well as physiological and biochemical changes in grapevines grown in soils containing excess Cu. Methods The grapevines were collected during two productive cycles from three vineyards with increasing concentrations of Cu in the soil and at various growth stages, before and after the application of Cu-based fungicides. The Cu concentrations in the grapevine organs and the macronutrients and biochemical parameters in the leaf blades were analyzed. Results At close to the flowering stage of the grapevines, the concentration and content of Cu in the leaves were increased. However, the Cu concentrations in the roots, stem, shoots and bunches did not correlate with the metal concentrations in the soil. The application of Cu-based fungicides to the leaves increased the Cu concentrations in the shoots, leaves and rachis; however, the effect of the fungicides on the Cu concentration in the berries was not significant. The biochemical analyses of the leaf blades demonstrated symptoms of oxidative stress that correlated with the Cu concentrations in soil. Conclusions The increased availability of Cu in soil had a slight effect on the levels and accumulation of Cu in mature grapevines during the productive season and did not alter the nutritional status of the plant. However, increased Cu concentrations were observed in the leaves. The evidence of oxidative stress in the leaves correlated with the increased levels of Cu in soil.

Description: Information regarding changes in soil condition after reforestation may help in inferring environmental and ecosystem benefits. A case study was undertaken in Victoria State, Australia, to investigate the changes in soil condition after reforestation of a deforested creek bank to infer environmental benefits. The study was conducted at four sites in a large farm. At each site a ~150 m strip of land that ran perpendicular to a creek from the bank to cropping area was selected. The results show that total organic carbon (TOC) and total mineral nitrogen (TN) in the cropped segment (CS) of a strip at a given site were significantly higher than in the corresponding reforested segment (RS) which in turn was higher than in the bare segment (BS) whilst the electrical conductivity (EC) and bulk density (BD) were in the order BS 〉 RS 〉 CS. Six years after reforestation, TOC and TN in the RS increased by 30 and 24 %, respectively, compared with 9 and 8 % for 3 years. The EC, BD, and pH decreased by 26, 14, 14 %, respectively, 6 years after reforestation. Creek bank reforestation associated improvements in TOC, TN, BD, EC, and pH may have positive impact on pollutant and salinity abatement.

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:    Successful revegetation of saline land is dependent on seedling recruitment to maintain vegetative cover for lowering of saline water tables and agricultural production. This paper examines seasonal effects of tree/shrub microsites and leaf-litter on soil conditions and seedling recruitment in a saline grazing system planted with Eucalyptus sargentii Maiden tree rows (15 years old) and saltbush ( Atriplex spp.) inter-rows (8 years old). Salt bush rows were also slightly mounded. As litter accumulation decreases with increased distance from tree rows, soil conditions and seedling recruitment were compared between paired bare and litter-covered zones within three microsites: tree row, saltbush row 1 (saltbush row closest, viz. 3–4 m, to tree row) and saltbush mid-row (middle row of saltbush between adjacent tree rows, viz. 7–9 m from trees). Microsite facilitation in winter was negligible due to moderate temperatures and high water availability. However, in warmer months, saltbush mid-row microsites were most favourable for recruitment. Tree microsites inhibited recruitment through increased salinity, water repellency and potential root competition. Despite negative interactions within the tree row, trees indirectly facilitated recruitment through litter provision in saltbush rows. Overall, litter increased seedling densities through amelioration of soil temperatures and salinity. Litter reduced salinity (top 2 cm) in warmer months, from ‘severe’ where only halophytes survive, to ‘moderate’ where growth of non-halophytic species is possible, but at reduced rates. Recruitment was influenced by microsite characteristics including, litter quantities, mounding and row position. Content Type Journal Article Pages 1-13 DOI 10.1007/s11104-011-0850-7 Authors Claire Farrell, School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia Christopher Szota, School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia Richard J. Hobbs, School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia Timothy D. Colmer, School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X

Description:    Warming and elevated atmospheric CO 2 (eCO 2 ) can elicit contrasting responses on different SOM pools, thus to understand the effects of combined factors it is necessary to evaluate individual pools. Over two years, we assessed responses to eCO 2 and warming of SOM pools, their susceptibility to decomposition, and whether these responses were mediated by plant inputs in a semi-arid grassland at the PHACE ( P rairie H eating a nd C O 2 E nrichment) experiment. We used long-term soil incubations and assessed relationships between plant inputs and the responses of the labile and resistant pools. We found strong and contrasting effects of eCO 2 and warming on the labile C pool. In 2008 labile C was increased by eCO 2 and was positively related to plant biomass. In contrast, in 2007 eCO 2 and warming had interactive effects on the labile C, and the pool size was not related to plant biomass. Effects of warming and eCO 2 in this year were consistent withtreatment effects on soil moisture and temperature and their effects on labile C decomposition. The decomposition rate of the resistant C was positively related to indicators of plant C inputs. Our approach demonstrated that SOM pools in this grassland can have early and contrasting responses to climate change factors. The labile C pool in the mixed-grass prairie was highly responsive to eCO 2 and warming but the factors behind such responses were highly dynamic across years. Results suggest that in this grassland the resistant C pool could be negatively affected by increases in plant-production driven available soil C. Content Type Journal Article Pages 1-12 DOI 10.1007/s11104-011-0853-4 Authors Yolima Carrillo, Department of Botany, University of Wyoming, Laramie, WY 82071, USA Elise Pendall, Department of Botany, University of Wyoming, Laramie, WY 82071, USA Feike A. Dijkstra, Faculty of Agriculture, Food and Natural Resources, The University of Sydney, Level 4, Biomedical Building—C81, Australian Technology Park, Eveleigh, NSW 2015, Australia Jack A. Morgan, Rangeland Resources Research Unit, USDA-ARS, Crops Research Laboratory, 1701 Center Ave, Fort Collins, CO 80526, USA Joanne M. Newcomb, Department of Botany, University of Wyoming, Laramie, WY 82071, USA Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X

Description:    Recent studies suggest that phosphatase activity in soil under legumes is higher than under other plants, but whether this is due to plant activity, microbe activity, or a response to altered soil N or P is unclear. I addressed two main questions: (i) do legumes have a higher root phosphomonoesterase (PME) activity than non-legumes?, and (ii) does root PME activity of legumes and non-legumes respond differently to variation in P or N supply? In four greenhouse experiments, I compared PME activity of seven leguminous forbs and nine other herb species (mostly forbs), under various supplies of inorganic P or N. Under low P and high N supply, legumes had on average a 50% or 120% higher PME activity than other forbs (expressed per fresh or dry roots). Legumes were similar or more plastic in their response to gradients of P, but less plastic to gradients of N. Root PME activity did not seem to depend on the presence of nodules, nor on growing in species monocultures or mixtures. On average leguminous forbs do have a higher root PME activity than other forbs, particularly under low inorganic P and N supply. Under higher N supply, the difference between leguminous and non-leguminous forbs becomes smaller, and PME activity of grasses may even be higher than that of legumes. The results help explaining why legumes can become abundant in plant communities on P and N-poor soils. Content Type Journal Article Pages 1-10 DOI 10.1007/s11104-011-0834-7 Authors Harry Olde Venterink, Institute of Integrative Biology, ETH Zurich, Universitätsstrasse 16, 8092 Zurich, Switzerland Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X

Description:    Forest plantations and agroforestry systems with Schizolobium parahyba var. amazonicum have greatly expanded in the Brazilian Amazon, generally as an alternative for reforesting degraded areas. To our knowledge there are no reports of above- and below-ground production in these forest systems. We quantified litter and fine root production in 6-yr old Schizolobium -based plantation forests (monospecific: MON, mixture: MIX, and agroforestry system: AFS) and in ~25-yr old regrowth forest (REG) over 8–12 months. We used litter traps and ingrowth cores to quantify litter and fine root production, respectively. Annual litter production was significantly lower in Schizolobium -based plantations (mean ± standard error, MON = 5.92 ± 0.15, MIX = 6.08 ± 0.13, AFS = 6.63 ± 0.13 Mg ha −1  year −1 ) than in regrowth forest (8.64 ± 0.08 Mg ha −1  year −1 ). Schizolobium -based plantations showed significantly higher litter stock (MON = 7.7 ± 1.0, MIX = 7.4 ± 0.1 Mg ha −1 ) than REG (5.9 ± 1.3 Mg ha −1 ). Total fine root production over an 8-month period was significantly higher in Schizolobium -based plantations (MON = 3.8 ± 0.2, MIX = 3.4 ± 0.2, AFS = 2.7 ± 0.1 Mg ha −1 ) than in REG (1.1 ± 0.03 Mg ha −1 ). Six-yr old Schizolobium -based plantations and ~25-yr old regrowth forests showed comparable rates of litter + fine root production, suggesting that young forest plantations may be an interesting alternative to restore degraded areas due to early reestablishment of organic matter cycling under the studied conditions. Content Type Journal Article Pages 1-10 DOI 10.1007/s11104-011-0857-0 Authors Antonio Kledson Leal Silva, Universidade Federal do Para, Programa de Pos-graduacao em Ciencias Ambientais, Belem, Para, Brazil Steel Silva Vasconcelos, Embrapa Amazonia Oriental, Laboratorio de Ecofisiologia Vegetal, Belem, Para, Brazil Claudio José Reis de Carvalho, Embrapa Amazonia Oriental, Laboratorio de Ecofisiologia Vegetal, Belem, Para, Brazil Iracema Maria Castro Coimbra Cordeiro, Tramontina Belem S.A., Belem, Para, Brazil Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X

Description:    Several studies have shown that soil biotic communities from organically managed fields are more diverse and exhibit higher activity levels compared to conventionally managed fields. The impact of these different soil communities on plant productivity and the provision of soil ecosystem services are, however, still unclear. Here, we test the effects of soil inoculation from each of three organic and three conventional maize fields on maize productivity and nutrient loss during leaching events induced by simulated rain. In particular, we examine whether differences in productivity and nutrient loss are related to the abundance and species composition of arbuscular mycorrhizal (AM) fungi. We hypothesized that soil biota from organically managed fields would improve maize growth and reduce nutrient leaching significantly more than those from conventionally managed fields. In contrast to our hypothesis, we found that plant productivity was negatively affected by soil inoculation, and this effect was stronger with inoculum from organic fields. Plant productivity was inversely correlated with AMF abundance, suggesting that enhanced carbon allocation to AMF is at least in part responsible for plant growth reduction under our experimental conditions. However, soil inoculation did alter the ecological functioning of the system by reducing phosphorus leaching losses after simulated rain. Moreover, these leaching losses were lower with increased hyphal density and were related with abundance of particular AMF types, suggesting that abundance of AMF and their community composition may be useful indicators of phosphorus leaching losses. The results demonstrate that soil communities from different agricultural fields vary in their impact on plant productivity and nutrient leaching losses. The results further indicate that there is a potential tradeoff between positive effects of soil communities on sustainability and negative effects on crop productivity. Content Type Journal Article Pages 1-13 DOI 10.1007/s11104-011-0828-5 Authors Erik Verbruggen, Department of Ecological Science, Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, the Netherlands E. Toby Kiers, Department of Ecological Science, Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, the Netherlands Patrick N. C. Bakelaar, Department of Ecological Science, Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, the Netherlands Wilfred F. M. Röling, Molecular Cell Physiology, Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, the Netherlands Marcel G. A. van der Heijden, Department of Ecological Science, Faculty of Earth and Life Sciences, VU University Amsterdam, Amsterdam, the Netherlands Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X

Description:    For establishing rational farming mechanism, it is essential to know the relative contribution of different geological background and anthropogenic activities to trace elements in agricultural soil. In this paper, 282 surface soil samples were collected based on the different geological background. Five harmful trace elements (As, Cd, Cr, Hg and Pb) were analyzed. The results indicated most of trace elements contents were far beyond the threshold of uncultivated soil background, which indicate anthropogenic input strongly influenced on trace elements in agricultural soil. In addition, correlation analysis showed trace element contents exhibited high relationships with soil pH, C/N and physical clay (〈0.01 mm) ( p  〈 0.05). The principal component analysis showed that the first component included Cd, Cr and Hg, while Pb and As formed the second component. Furthermore, in the agricultural topsoil derived from carbonate rock, the high background values of trace elements and alkaline condition made the enrichments of Cd, Cr and Hg were the most significant. In the agricultural topsoil derived from red residua, the Pb and As contents was the highest values among the soil categories, partly because the type of soil had amount of physical clay (〈0.01 mm). In the agricultural topsoil derived from shale, the pH or physical clay had significant relationship with Cd, Pb, Hg and As ( p  〈 0.01). In the agricultural topsoil derived from sand stone, the acid condition and loose texture might account for the lowest values of Cd, Cr, Pb and As content to some extent. Content Type Journal Article Pages 1-11 DOI 10.1007/s11104-011-0866-z Authors Chenglong Tu, State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550002 China Tengbing He, Agricultural college, Guizhou University, Guiyang, 550001 China Congqiang Liu, State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550002 China Xiaohui Lu, School of Geographic and Environmental Sciences, Guizhou Normal University, Guiyang, 550001 China Yunchao Lang, State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550002 China Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X

Description: Genes do not form channels Content Type Journal Article Pages 1-3 DOI 10.1007/s11104-011-0872-1 Authors Dev T. Britto, Department of Biological Sciences, University of Toronto, Toronto, ON, Canada M1C 1A4 Herbert J. Kronzucker, Department of Biological Sciences, University of Toronto, Toronto, ON, Canada M1C 1A4 Journal Plant and Soil Online ISSN 1573-5036 Print ISSN 0032-079X