Selenium species transforming along soil–plant continuum and their beneficial roles for horticultural crops

Selenium(Se)acquirement from daily diet can help reduce the risk of many diseases.The edible parts of crop plants are the main source of dietary Se,while the Se content in crops is determined by Se bioavailability in soil.We summarize recent research on the biogeochemical cycle of Se driven by specific microorganisms and emphasize the oxidizing process in the Se cycle.Moreover,we discuss how plant root exudates and rhizosphere microorganisms affect soil Se availability.Finally,we cover beneficial microorganisms,including endophytes,that promote crop quality and improve crop tolerance to environmental stresses.Se availability to plants depends on the balance between adsorption and desorption,reduction,methylation and oxidation,which are determined by interactions among soil properties,microbial communities and plants.Reduction and methylation processes governed by bacteria or fungi lead to declined Se availability,while Se oxidation regulated by Se-oxidizing microorganisms increases Se availability to plants.Despite a much lower rate of Se oxidization compared to reduction and methylation,the potential roles of microbial communities in increasing Se bioavailability are probably largely underestimated.Enhancing Se oxidation and Se desorption are crucial for the promotion of Se bioavailability and uptake,particularly in Se-deficient soils.Beneficial roles of Se are reported in terms of improved crop growth and quality,and enhanced protection against fungal diseases and abiotic stress through improved photosynthetic traits,increased sugar and amino acid contents,and promoted defense systems.Understanding Se transformation along the plant-soil continuum is crucial for agricultural production and even for human health.

Impacts of competition and nitrogen addition on plant stoichiometry and non-structural carbohydrates in two larch species

Previous research has shown that competition between plants can have differential effects on leaf stoichiometry and non-structural carbohydrate(NSC)in different environments.However,little attention has been given to understanding these effects on non-photosynthetic organs,particularly of deciduous tree species.Here we assess the impact of competition on below and aboveground biomass,stoichiometry,nutrient composition and NSC in pure and mixed forests of two Larch species,Larix kaempferi and L.olgensis under nitrogen(N)addition.Nitrogen enrichment did not result in stronger intraspecific competition for both species and L.olgensis benefited from the presence of L.kaempferi under different N levels.Stems kept relatively stable C/N compared to roots and branches in response to competition,while N addition imposed stronger impacts on N/P of different organs rather than competition.In contrast to stable C concentrations,starch and soluble sugar concentrations were more easily impacted by competition and the addition of nitrogen.Competition forced L.kaempferi and L.olgensis to allocate more carbon into storage by increasing their starch concentration and starch/soluble sugar of stems under competition.However,no significant differences in stoichiometry and NSC concentration between intra-and interspecific competition were found.NSC and nutrient pools of L.kaempferi stems,branches and coarse roots consistently declined due to competition regardless of N addition.Coarse and fine roots of L.kaempferi accumulated more N when in competition with L.olgensis than with a conspecific neighbor under N addition.Our results show that NSC was more sensitive to competition relative to stoichiometric traits(N and P)of non-photosynthetic organs.