Description: Background and aims Modern maize breeding has increased maize yields worldwide. The changes in above-ground traits accompanying yield improvement are well-known, but less information is available as to the effect of modern plant breeding on changes in maize root traits. Methods Root growth, nitrogen uptake, dry matter accumulation and yield formation of six maize hybrids released from 1973 to 2000 in China were compared. Experiments were conducted under low and high nitrogen supply in a black soil in Northeast China in 2010 and 2011. Results While nitrogen accumulation, dry matter production and yield formation have been increased, modern maize breeding in China since 1990 has reduced root length density in the topsoil without much effect on root growth in the deeper soil. The efficiency of roots in acquiring N has increased so as to match the requirement of N accumulation for plant growth and yield formation. The responses of root growth, nitrogen and dry matter accumulation, and grain yield to low-N stress were similar in the more modern hybrids as in the older ones. Conclusions Modern maize breeding has constitutively changed root and shoot growth and plant productivity without producing any specific enhancement in root responsiveness to soil N availability.

Description: Aims Nitrous oxide (N 2 O) emissions from pastoral agriculture are considered to originate from the soil as a consequence of microbial activity during soil nitrification and denitrification. However, recent studies have identified the plant canopy as a potentially significant source of N 2 O emissions to the atmosphere. Understanding the extent and mechanisms of plant emissions may provide new mitigation opportunities as current options only target soil microbial processes. Methods We developed an experimental apparatus and protocol to partition N 2 O emissions between the leaves of grasses and the soil and measured emissions from ten common grass species found in New Zealand pastures. Results The chamber design enabled us to identify measurable changes in N 2 O concentration over a period of 1 h and to distinguish a range of emissions from 0.001 to 0.25 mg N 2 O-N/m 2 leaf area/h. There was a 10-fold variation among species; Holcus lanataus , Lolium perenne and Paspalum dilatatum had the highest leaf N 2 O emissions and Poa annua the lowest. Conclusions Grasses do emit N 2 O from their leaves and the rate that this occurs varies among grass species. The emission does not appear to arise from formation of N 2 O in plant leaves but more likely reflects transport of N 2 O from the soil. Differences in emission rates appear to arise from a plant influence on the rate of formation of N 2 O in the soil rather than the rate of transportation through the plant.

Description: Background and aims Drivers of ecosystem dynamics that are under human influence range from local, land-management decisions to global processes such as warming temperatures and N deposition. The goal of this study was to understand how multiple, potentially interacting factors influence net primary production, N mineralization, and water and soil CO 2 fluxes. Methods Here I report on a three-year experiment that manipulated air temperature using ITEX passive warming cones and N deposition in a mountain meadow ecosystems that were historically grazed or protected from grazing. Results The strongest and most consistent effect was due to the legacy of grazing, with previously grazed sites having lower primary production, lower soil respiration rates, lower soil moisture, and lower soil C and N stocks than historically ungrazed sites. Warming increased soil respiration, but the effect was transient, and decreased over the 3-year study. Nitrogen addition increased primary production in the second and third year of the experiment but had no significant effect on soil respiration. The effect of historical grazing on primary production was approximately double the effect of N addition. Temperature and N deposition rarely interacted except for increasing N availability during the warm, wet growing season of 2004. Conclusions These findings indicate that the legacies of land use, with their influence on plant community composition and hydrologic processes, are locally more important than short-term step changes in temperature and nutrient availability.

Description: Background and aims Recent studies suggest that root border cells function in defense of the root by an extracellular DNA-based trapping mechanism similar to that described in mammalian white blood cells. Genes controlling the specialized properties of border cells as they detach from the root tip therefore are of interest. Methods mRNA differential display was used to identify Brd13 , a sequence expressed in border cells but not other root tissues. RNase protection and mRNA Northern blot analyses, and reporter gene expression under the control of the Brd13 promoter in transgenic hairy roots were used to confirm localized expression. Phenotype analysis of transgenic hairy roots expressing Brd13 antisense mRNA was carried out. Results Brd13 was expressed constitutively in border cells but not in leaves, stems, or roots without border cells. The predicted protein shares sequence similarity with flavin-binding proteins. Transgenic hairy roots expressing Brd13 antisense mRNA exhibited abnormal growth and morphology. Conclusions We report here that altered expression of a putative flavin-binding protein in border cells resulted in altered root development. Flavin-binding proteins play key roles in development, defense, and local auxin biosynthesis. The Brd13 gene and its promoter may be useful in creating defined changes in root development and defense.

Description: Background and aims The total concentration of dissolved organic carbon (DOC) has often been observed to correlate positively with soil microbial respiration. The aim was to explain the correlation with the properties of dissolved organic matter (DOM). Methods A dataset from previously published papers was gathered together and subjected to multivariate analyses. Samples were collected from five tree species experiments in Finland. The degradability of DOM was assessed by measuring bacterial and fungal growth in DOM. The chemical properties of DOM were assessed by XAD resin fractionation and molecular weight. Soil microbial activity was assessed as C and N mineralization and microbial biomass. Results Both low and high molecular weight compounds, as well as hydrophilic neutral compounds, seemed to be relatively easily degradable. In contrast to our presupposition, easily degradable DOM seemed to be less abundant in soil where variables describing microbial activity were higher. Birch soil with higher microbial biomass N seemed to contain less easily degradable DOM than spruce soil. Conclusion We suggest that DOM collected and characterized at a certain point reflects more the accumulation of refractory compounds following high microbial activity than the easily degradable compounds that microbes would be using when measured.

Description: Aims Heavy-metal tolerance is a widespread phenotype in bacteria, particularly occurring in strains isolated from heavy-metal contaminated sites. Concerning nickel tolerance, the nre system is one of the most common. An ortholog of the nreB gene is present in the alfalfa symbiont Sinorhizobium meliloti also, which stir the attention on its functional role in such Ni-sensitive species and on the evolutionary relationships with Ni-resistant strain orthologs. Methods Phylogenetic reconstruction and comparative genomics were performed to analyze the phylogenetic relationships of nreB orthologs, as well aa nreB deletion mutant S. meliloti strain was constructed and subjected to phenotypic analysis. Results Phylogenetic analysis of nreB genes indicated horizontal gene transfer events, possibly mediated via mobile genetic elements. Phenotype Microarray, biochemical and symbiotic analyses of the deletion mutant strain (Δ nreB ) showed that in S. meliloti nreB is involved in the tolerance to several stresses other than Ni (mainly urea and copper), possibly partially mediated through the modulation of urease and hydrogenase activities. Conclusions Obtained results allowed us to speculate that nreB is a highly mobile gene cassette, spread in the bacterial phylogenetic tree via many HGT events, which could have been recruited to confer nickel-tolerance in strains thriving in contaminated environments, by small changes linked to its basic functions (e.g. modulation of urease and hydrogenase activity).

Description: Background and aims Nitrogen (N 2 ) fixation in feather moss-cyanobacteria associations is a major source of N for boreal ecosystems. However, mosses experience significant shifts in their moisture status due to daily and yearly fluctuations in sunlight, temperature and precipitation. While the effects of drying and rewetting on nutrient leaching and photosynthesis in mosses have been studied, no attempt has been made to assess the consequences for N 2 fixation in feather mosses. Methods We conducted an experiment in which we dried (3 day at 28 °C; 〈9 % of field moisture) and rewetted samples of the feather moss Pleurozium schreberi (Brid.) Mitt. that is colonized by N 2 -fixing-cyanobacteria to assess the influence on N 2 fixation. Further, we tested how long it takes for N 2 fixation to recover from a drying-rewetting cycle. In addition, we assessed how N 2 fixation changes with incubation time with acetylene (2–65 h). Results A drying period of 3 days almost completely eliminated N 2 fixation (〈0.2 μmol m −2  h −1 ) in the moss. However, rates slowly recovered after rewetting, reaching N 2 fixation levels of moist (non-water stressed) moss 5 days after rewetting. Nitrogen fixation increased significantly with incubation time with acetylene (0 μmol m −2  h −1 at 2 h vs. 26 μmol m −2  h −1 at 65 h incubation). Conclusions Although N 2 fixation recommenced upon rewetting, the recovery was slow. Thus, recurrent drying and rewetting cycles could reduce total N 2 fixation in moss-cyanobacteria associations over time, leading to reduced total N input to the system.

Description: Background and aims Reduced tillage is widely used in maintaining sustainable agricultural systems. Early growth of wheat ( Triticum aestivum L.) is often impaired in the high strength soils typical of no-till. This may reflect the intrinsically reduced vigour of commercial wheat varieties. We investigated how genotypes selected for greater early vigour performed relative to a broader range of wheat genotypes for shoot and root growth in cultivated and no-till conditions. Methods We assessed a range of cereal germplasm varying for early growth (establishment and leaf area development) under contrasting tillage conditions in a very favourable season, and then the performance of a selected subset validated in repacked soil cores in controlled environments. We measured above- and belowground growth, and parameters associated with adaptation to increasing soil strength. Results High strength soil reduced early shoot and root growth. There were no effects on plant number at emergence and coleoptile length was unimportant. Increased soil strength reduced early growth of all genotypes including genetically vigourous wheats. However, the ranking for vigour was maintained with high strength soil suggesting breeding lines and populations containing genes for greater early growth may still be beneficial in selection for improved performance in no-till. Genotypic increases in specific leaf area and leaf breadth were both associated with genetically greater seedling leaf area and biomass, and potential for greater root growth in no-till. Conclusions Early growth of all wheats was reduced with no till and the harder, high strength soil associated with this tillage system. Genetic variation was large in no-till and cultivated soils alike. In high strength and no-till soils, the relationship with shoot and root vigour was positive indicating selection for greater early growth in breeding programs may increase leaf area and improve root growth.

Description: Aims The aim of this study was to examine the effect of plant species differing in functional and phylogenetic traits on the decomposition processes of leaf litter in a grassland of Japanese pampas grass ( Miscanthus sinensis ) and adjacent forests of Japanese red pine ( Pinus densiflora ) and Japanese oak ( Quercus crispula ), representing sequential stages of secondary succession. Methods The litterbag experiments were carried out for 3 years in a temperate region of central Japan. Results The decomposition constant (Olson’s k) was 0.49, 0.39, and 0.56/year for grass, pine, and oak, respectively. Nitrogen mass decreased in grass leaf litter during decomposition, whereas the absolute amount of nitrogen increased in leaf litter of pine and oak during the first year. Holocellulose in grass leaf litter decomposed selectively over acid-unhydrolyzable residues more markedly than in leaf litter of pine and oak. 13 C nuclear magnetic resonance analysis also revealed a decrease in the relative area of O-alkyl-C in grass. Conclusions The different decomposition among the three litter species implied that the secondary succession from grassland to pine forest and from pine to oak forests could decrease and increase, respectively, the rate of accumulation and turnover of organic materials and N in soils.

Description: Background and aims MYB transcription factors play critical roles in plant development and stress responses. Our objective was to characterize a role of AtMYB20 (AT1G66230) in regulating the ABA-dependent adaptive response to desiccation stress in Arabidopsis. Methods Sequencing analysis revealed that there is a site located on the AtMYB20 transcript which is potentially base-paired by miR858. To avoid the possible cleavage, a vector with a miR858-resistant version of AtMYB20 under the CaMV 35S promoter ( 35S:m5AtMYB20 ) was constructed. The AtMYB20 knock-out mutant myb20 was applied to identifying AtMYB20 functions. Results While AtMYB20 was induced by high levels of NaCl, its expression was suppressed by desiccation and cold stresses and abscisic acid (ABA) treatment. Compared with wild-type, AtMYB20 over-expression ( 35S:m5AtMYB20 ) seedlings were susceptible to desiccation, whereas MYB20 loss of function mutant myb20 plants displayed resistance to desiccation stress. 35S:m5AtMYB20 plants were less sensitive to ABA, but myb20 mutants were hypersensitive to ABA. This could be validated by the experiment in which treatment with 10 μM ABA for 2 h resulted in constant stomatal opening on leaves of 35S:m5AtMYB20 plants but stomatal closure on myb20 mutant plants. Expression of ABA- and drought stress-responsive marker genes ( e.g. ABI3-5 and ABF3-4 ) was up-regulated in myb20 plants but down-regulated in 35S:m5AtMYB20 plants. Conclusions AtMYB20 acts as a negative regulator of plant response to desiccation stress in an ABA-dependent manner.