Study On The Mechanism Of Combined Application Of Phosphorus And Selenium Uptake Winter Wheat And Selenium Utilization In Soil

Selenium（Se）is an essential micro-element for humans,and plays important roles in disease prevention,enhance immune system and prevent cancer.Studies also have shown that 72% of soil was Se deficient in China.The total selenium and available Se content in soil directly affected the uptake and accumulation of Se by crops.Phosphorus is the second essential element for plant growth and development,however,phosphorus is easily combined with soil solid components,resulting in poor solubility and slow diffusion,so the content of available phosphorus is reduced.Due to the similarity of physical and chemical properties between phosphate and selenite.Phosphorus supply often significantly impacts the absorption,translocation and metabolism of Se in plants.In this text,we studied the effect of the combining of phosphorus and Se fertilization on the plant growth,phosphorus and selenium absorption and translocation,subcellular distribution,Se species in plant,available phosphorus concentration in soil,Se chemical forms transformation and microbial community by hydroponic,rhizbox and pot and field experiment and investigated the plausible mechanisms of P and Se interaction effect of winter wheat,improved the availability of soil P and Se,and explored the appropriate combined application concentration of P and Se.The results showed that:1.In order to explore effect of combined application of P with three kinds of Se fertilizer on the Se uptake,translocation,subcellular fraction and species of winter wheat by a hydroponic experiment.The resulted showed that: P combined with Se could enhance photosynthesis and increase root parameter,and then promote the dry matter weight of shoots and roots.An increase in P supply significantly decreased Se concentration in shoots and roots at selenite and Se Met.At selenate,an increase in P supply significantly increased Se concentration in shoots and roots,increased Se migration coefficient form roots to shoots and Se accumulation in shoots.An increase in P supply inhibited distribution of Se in root cell wall but increased distribution of Se in root soluble fraction,reduced Se migration coefficient form roots to shoots at selenite,but there were no significant influence on Se subcellular fraction at selenate and Se Met.An increase in P supply alter the chemical forms of Se in tissues of winter wheat under three kinds of Se fertilizer.Compared with selenate or Se Met treatment,appropriate P combined with selenite could enhance the photosynthesis and promote plant growth,reduce Se uptake,alter Se subcellular distribution and speciation,and affect Se bioavailability in winter wheat.2.In order to the explore effect of combined application of P with Se on the availability and chemical fractions of Se in root-soil interface of winter wheat by a rhizobox culture experiment.The resulted showed that: at Se₁,P application（P80 and P160）significantly increased Se accumulation in each tissue,but significantly reduced Se concentration in shoots and Se migration coefficient form roots to shoots.At Se₀,P160 treatment increased the concentration of exchangeable Se in rhizosphere and nonrhizosphere soil.At Se₁,the concentration of exchangeable Se in the rhizosphere soil was higher than non-rhizosphere soil,but the concentration of iron-manganese and residual Se were lower than non-rhizosphere soil.Appropriate combined application of P with Se promoted transformation of chemical forms of Se in soil,enhanced Se absorption and accumulation of winter wheat,which may be due to the combined effect of P application and root activity promoting transformation of Se from ironmanganese and organic sulfide bound Se to exchangeable Se to improve the bioavailability of Se in soil.3.In order to explore the effects of combined application of P and Se on the microbial community structure and diversity in rhizosphere soil by a pot experiment.The resulted showed that: at Se₀ and Se_0.5,P application significantly increased P concentration and accumulation in each tissue,but significantly decreased root,straw/leave and grain Se concentration.The grain,glume and straw/leave Se accumulation were firstly increased and then decreased with the increasing P application at Se_0.5,where the highest value appeared under the P_0.2 treatment.Se application significantly increased Se concentration and accumulation in each tissue,decreased P concentration and accumulation in each tissue at P_0.2 and P_0.4.At Se_0.5,P application significantly increased available phosphorus concentration and increased the Se concentration and proportion of water-soluble in soil,and Se application significantly increased available phosphorus concentration at P_0.4.At Se_0.5,P_0.2 and P_0.4 treatments significantly increased the relative abundance of Actinobacteria and Gemmatimonadetes,respectively,but both significantly decreased the relative abundance of Bacteroides.Se application significantly increased the relative abundance of Actinobacteria at P_0.2 and Acidobacteria at P_0.4.At Se_0.5,compared with P0,P_0.2 treatment significantly increased Shannon index.At P_0.2,Se application significantly increased Simpson index.Appropriate combined application of P with Se altered the microbial community in soil and promoted the release of P and Se in soil,and then increased soil available P and Se content,enhanced the promoting effecting of P on grain yield of winter wheat and increased the Se accumulation of grain under Se_0.5P_0.2 treatment.4.In order to investigate the effects of combined application on P and Se on grain yield and organic selenium species in grains of winter wheat by a pot and field experiment.The result showed that: the yield of winter wheat was significantly increased by the combination application of P and Se in the pot experiment,the yield of winter wheat was the highest under P₈₀Se₁ treatment.But Se application（25 g·mu-1）significantly decreased yield of winter wheat at P₉₀ and P₁₃₅ in the field experiment.In the pot experiment,Se application increased the proportion of total Se accumulated in the grains and roots of winter wheat,but decreased the ratio of total Se accumulated in glumes.Se application increased the organic Se concentration in grains,Se in winter wheat grains was mainly in the organic form including selenomethionine and selenocystine.Selenomethionine and inorganic Se concentration in grains decreased with the increasing P application.In the field experiment,soil application 25 g·mu-1（Se S25）and spraying application 100 mg·kg^-1(Se P₁₀₀)significantly increased Se concentration of winter wheat.The Se concentration and accumulation in each tissue in spraying application treatment were high than in soil application treatment.Appropriate P combined with Se application enhanced grain yield of winter wheat,promoting the transfer of selenium in the winter wheat to the grain,increased Se accumulation and organic Se concentration of grain.