ALBERT

Description: Background and aims Soil amendments are often added to polluted soils to increase phytoremediation efficiency. Here we investigated the potential of a range of organic amendments for phytoextraction of heavy metals in a contaminated sediment. Methods Two experiments compared adsorption and phytoextraction of heavy metals by a Cd-hyperaccumulator Carpobrotus rossii grown in the contaminated sediment amended with six organic amendments. Results The adsorption capacity as measured by Langmuir adsorption maximum followed the order of Cr 〉 Zn 〉 Cu 〉 Cd, and the effect of organic amendments followed the order of chicken manure 〉 cow manure 〉 brown coal 〉 golden wattle biochar 〉 blue gum biochar 〉 radiata pine biochar. The addition of amendments increased the adsorption of heavy metals, with brown coal resulting in the lowest concentrations of water-extractable Cd, Cu and Zn. Two manures resulted in the highest concentrations of these water-extractable heavy metals in the rhizosphere soil of C. rossii. Furthermore, brown coal resulted in higher shoot accumulation of these heavy metals than three wood-derived biochars, whilst the manures generally had the lowest accumulation of Cd and Cu although they increased shoot biomass. Conclusions The addition of brown coal decreased whereas manure addition increased the mobility (water-extractable fraction) of heavy metals in rhizosphere soil. Phytoextraction of Cd and Cu was greater with brown coal than with biochars or manures. Brown coal is suitable for enhancing phytoextraction of these heavy metals because it could increase their accumulation in shoots of C. rossii and decrease the risk of leaching of these heavy metals into groundwater.

Description: Background and aims Cicer canariense has been shown to be a promiscuous legume. The symbiotic characteristics of several C. canariense mesorhizobial genospecies harbouring similar symbiotic genes are studied. Methods Comparative analysis of nodA and nifH gene phylogenies, and characterization of the symbiotic phenotypes on the basis of nodulation and nitrogen fixation was performed. Results Phylogenetic analyses of the nodulation gene nodA was in complete agreement with those previously done on nodC in grouping these mesorhizobia within symbiovar loti. In the nifH phylogeny, however, these strains were resolved into two subgroups named nifH-1 and nifH-2 . Subgroup nifH -1 contained strains from two genospecies and correlates with symbiovar loti, as it clustered with Mesorhizobium reference strains nodulating Lotus corniculatus . In contrast, subgroup nifH -2 contained strains of the other seven genospecies without reference strains and formed a distant branch on its own. Strains combining symbiovar loti genes in any chromosomal background effectively nodulated C. canariense , although with significant differences in nitrogen fixation capabilities. Conclusions Symbiovar loti genes are the most widely spread in the mesorhizobia that nodulate C. canariense in its natural habitat. They included two variants of the nifH gene and were found to be associated with nine chromosomal backgrounds (genospecies), resulting in strains showing different symbiotic effectiveness. Mesorhizobium tamadayense symbiovar loti strains were the most effective in this legume.

Description: Background and Aims Competition between intercropped species is important for yield advantage, but little attention has been given to interspecific competitive dynamics in intercropping. Methods A field experiment with five cropping systems (wheat/maize, barley/maize intercropping, wheat, maize and barley sole cropping), two N levels (0 and 225 kg N ha −1 ) and two maize mulching treatments (with and without) were performed. Sequential harvest of subplots was performed between 7 and 10 times, and the data were fitted to a logistic growth model. Results Intercropping significantly increased the maximum biomass and maximum growth rates of wheat and barley, but suppressed the early and maximum growth rate of intercropped maize. Maize growth recovered after the wheat or barley was harvested. In the presence of film mulch and/or fertilization, maximum biomass of intercropped maize was close to or significantly higher than that of maize alone. Fertilization and film mulching had much stronger effects on growth of maize than on wheat and barley. Conclusions Interspecific competitive dynamics regulated by fertilization and film mulching can be quantified by the logistic model, which is helpful to understand the yield advantage of intercropping. This has important implications for managing interspecific competition through agronomic practices at field.

Description: Background and aims Take-all, caused by the soilborne pathogen Gaeumannomyces graminis var. tritici , ( Ggt ), is an important root disease of wheat. Continuous wheat cropping has been shown to induce take-all decline (TAD). This research investigated the mechanisms of TAD in 13 New Zealand soils in two experiments and identified the associated microorganisms using denaturing gradient gel electrophoresis (DGGE). Methods In Experiment 1, a sterile sand/maize-meal mixture inoculated or not inoculated with Ggt , was added at 4 % ( w / w ) to sterilised and non-sterilised soils to determine their ability to suppress take-all, and to help identify the nature of suppression. Experiment 2 investigated the transferability of suppressive properties in five of the soils from Experiment 1. The microbial communities of these five soils were analysed using PCR-DGGE. Results Ten of the soils were able to suppress take-all but the suppression was biological in nature in only four of these soils. The suppressive properties of two of the soils were transferred to a γ-irradiated base soil amended with Ggt , indicating that suppression could be specific in nature (i.e., attributed to a specific microorganism or group of microorganisms). The suppressive properties in one soil were not transferrable, suggesting a general form of suppression, most probably because the conditions in the soil were suitable for other microorganisms to compete with Ggt . DGGE analyses of the microbial communities for five of the soils showed similar banding patterns for those with similar forms of suppression (specific, general and non-suppressive) and identified the potential microorganisms that distinguished them. Conclusion These distinguishing microorganisms are likely to independently or interactively have a function in suppressing take-all.

Description: Aims To determine the impact of long-term rabbit and sheep grazing on Salix repens N status (green and abscised leaf N content and C:N ratio), internal N dynamics and soil N supply rate in dune slacks. Methods Herbivore exclosures were erected in dune slacks at Ainsdale Sand Dunes NNR, creating three grazing treatments: rabbit grazing; rabbits excluded for 36 years; rabbit grazing followed by sheep and rabbit grazing for 18 years. Soil N supply rate was analysed using ion exchange membranes; leaf N dynamics of S. repens were measured over one summer. Results Soil N supply rate was higher in ungrazed plots. There was no difference in green leaf N MASS or C:N ratio between treatments, but N dynamics differed. Adding sheep to existing rabbit grazing reduced S. repens N resorption efficiency (R EFF ) from 67 to 37 %; excluding rabbits had no impact. Litter N MASS was lower and C:N ratio higher in ungrazed plots. Conclusions Grazing can impact significantly on leaf N resorption, but this impact depends on the grazing regime.

Description: Aims Maize ( Zea mays L.) is one of the most important crops worldwide. Despite several studies on maize roots, there is limited information on the function of different root types in extracting water from soils. Aim of this study was to investigate the location of water uptake in maize roots. Methods We used neutron radiography to image the spatial distribution of maize roots in soil and trace the transport of deuterated water (D 2 O) in soil and roots. Maize plants were grown in aluminum containers filled with a sandy soil that was kept homogeneously wet throughout the experiment. When the plants were 16 days old, we injected D 2 O into selected soil regions. The transport of D 2 O was simulated using a diffusion–convection numerical model. By fitting the observed D 2 O transport we quantified the diffusion coefficient and the water uptake of the different root segments. Results The root architecture of a 16 day-old maize consisted of a primary root, 4–5 seminal roots and many lateral roots. Laterals emerged from the proximal 15 cm of the primary and seminal roots. During both day and night measurements, D 2 O entered more quickly into lateral roots than into primary and seminal roots. The quick transport of D 2 O into laterals was caused by the small radius of lateral roots. The diffusion coefficient of lateral roots (4.68 × 10 −7  cm 2  s −1 ) was similar to that of the distal unbranched segments of seminal roots (4.72 × 10 −7  cm 2  s −1 ) and higher than that of the proximal branched segments (1.42 × 10 −7  cm 2  s −1 ). Water uptake of lateral roots (1.64 × 10 −5  cm s −1 ) was much higher than the uptake of seminal roots, which was 5.34 × 10 −10  cm s −1 in the proximal branched segments and only 1.18 × 10 −12  cm s −1 in the distal unbranched segments. Conclusions We conclude that the function of lateral roots is to absorb water from the soil, while the function of the primary and seminal roots is to axially transport water to the shoot.

Description: Aims Kin selection and resource partitioning have been proposed to explain interactions between plants growing with siblings (from the same mother). These mechanisms have been examined by measurements of fitness, phenotype or allocation traits, but have seldom been tested with N acquisition traits. Methods We determine if kin selection and resource partitioning are occurring using two annual species ( Sorghum vulgare and Glycine max ) with a short-term 15 N experiment. A mixture of ammonium, nitrate and glycine (1:1:1) was injected into soils around plants after they grew for 47 days. Only one nitrogen (N) form was 15 N labeled in each labeling solution. Results S. vulgare increased root allocation when growing with strangers (from the different mother), but not increase their N uptake. Although G. max strangers did not increase their root allocation, they significantly increased uptake of total N and the most abundant N form (nitrate) and decreased uptake of the least abundant (glycine). Conclusions G. max siblings reduced competition due to chemical resource partitioning while S. vulgare showed kin selection. We concluded that processes related to kin selection and resource partitioning can occur simultaneously, resulting in different competitive ability. These findings can improve our understanding of plants growing with siblings or strangers.

Description: Aims The aim was to devise a practical soil sampling design for oil palm plantations that takes into account tree-scale variability, thus facilitating detection of trends in soil properties over time. Methods We geometrically evaluated the ability of linear sampling transects to represent the distribution of typical management zones and radial patterns known to influence soil properties. The effect of sampling point density was tested using interpolated surfaces of soil biological, chemical and physical properties derived from values measured on a 35-point sampling grid covering the repeating tree unit in plantations with 15–25-year old palms. Results The ability of sampling transects to represent the proportion of the plantation in various zones improved with increasing transect length and sampling density. Increasing the number of sampling points from 10 to 50 (using an acceptably long transect with length 5.57 × palm spacing) decreased the maximum deviation between the overall mean and the transect-derived mean from 15.9 to 5.6 % for the most variable parameter, respiration, and 3.2 to 0.6 % for the least variable parameter, bulk density. Conclusions Transect sampling provides an efficient means of obtaining a composite soil sample that accounts for tree-scale variability in oil palm plantations. The method is readily adaptable for other tree crops.

Description: Background Botanists, ecologists and evolutionary biologists are familiar with the astonishing species richness and endemism of the fynbos of the Cape Floristic Region and the ancient and unique flora of the kwongkan of south-western Australia. These regions represent old climatically-buffered infertile landscapes (OCBILs) that are the basis of a general hypothesis to explain their richness and endemism. However, few ecologists are familiar with the campo rupestre of central and eastern Brazil, an extremely old mountaintop ecosystem that is both a museum of ancient lineages and a cradle of continuing diversification of endemic lineages. Scope Diversification of some lineages of campo rupestre pre-dates diversification of lowland cerrado , suggesting it may be the most ancient open vegetation in eastern South America. This vegetation comprises more than 5000 plant species, nearly 15 % of Brazil’s plant diversity, in an area corresponding to 0.78 % of its surface. Reviewing empirical data, we scrutinise five predictions of the OCBIL theory, and show that campo rupestre is fully comparable to and remarkably convergent with both fynbos and kwongkan , and fulfills the criteria for a classic OCBIL. Conclusions The increasing threats to campo rupestre are compromising ecosystem services and we argue for the implementation of more effective conservation and restoration strategies.