Effects Of Inoculation Of Arbuscular Mycorrhizal Fungi On Selenium Accumulation And Transformation Of Capsicum Annuum L.

Selenium is considered one of the 15 vital nutrients that the human body requires.In China,72%of regions suffer from selenium deficiency or have low selenium levels.Studies have found that mycorrhizal microbes play an important role in increasing the availability of selenium in plants.Pot experiments were used to investigate the differences in the growth of peppers inoculated with AMF（Arbuscular mycorrhizal fungi）and different concentrations of exogenous selenium,and the effects of selenium accumulation and transformation in pepper plants.The main results of this experiment are as follows:（1）The infection rate of AMF in pepper root systems was 71%when no selenium was applied.As the concentration of selenium increased,the infection rate initially increased and then decreased,reaching a maximum of 92%at an exogenous selenium concentration of 2 mg·L^-1,and a minimum of 67%at an exogenous selenium concentration of 16 mg·L^-1.（2）With increasing selenium concentration,the yield per pepper plant,plant height,stem diameter,root length,and fruit dry and fresh weight initially increased and then decreased.After inoculation with AMF,the highest yield per plant of pepper was achieved at a selenium concentration of 8 mg·L^-1,with the tallest plant height and longest root length.At this concentration,the stem diameter and fruit transverse and vertical diameter were also the largest.However,the heaviest fresh and dry weight of the pepper was observed at a selenium concentration of 4 mg·L^-1.（3）As the selenium concentration increased,the levels of capsanthin,total phenols,total flavonoids,vitamin C,and capsaicin in capsicum fruit initially increased and then decreased.After inoculation with AMF,the content of capsanthin in capsicum fruit was the highest when the selenium concentration was 4 mg·L^-1;the content of total phenols,total flavonoids,vitamin C,capsaicin and the scavenging rate of DPPH（Diphenyl-picryl hydrazide）and ABTS（2,2’-Biazo-bis-3-ethylbenzothiazoline-6-sulfonic acid）free radicals were the highest when the selenium concentration was increased to 8 mg·L^-1.（4）Without inoculation with AMF,the selenium content in each part of the pepper increased with increasing selenium concentration,and the selenium content in each part was higher after inoculation with AMF compared to the non-inoculated treatment.After inoculation with AMF,the selenium concentration in the fruit reached the maximum when the selenium concentration was 8 mg·L^-1.When not inoculated with AMF,the selenium transfer coefficients of leaves and fruits increased first and then decreased with the increase of selenium concentration.After inoculation with AMF,the transfer coefficients of Se in leaves and fruits increased with the increase of Se concentration.When the Se concentrations were 2 mg·L^-1,4 mg·L^-1 and 8 mg·L^-1,the transfer coefficients in stems,leaves and fruits were lower than those not inoculated with AMF.When AMF was not inoculated,the proportion of selenium content in the leaf cell wall gradually decreased with increasing selenium concentration,whereas the proportion of selenium content in the root,stem,and fruit cell wall increased initially and then decreased.Additionally,the proportion of selenium content in vacuoles and soluble components decreased at first and then increased.Compared with the same concentration of selenium treatment without AMF inoculation,the proportion of selenium content in leaf cell wall increased,and the proportion of selenium content in vacuoles and soluble components decreased.At Se concentrations 4 mg·L^-1 and 8 mg·L^-1,the proportion of Se content in stem cell walls increased after inoculation with AMF.When the selenium concentration was 4 mg·L^-1,8 mg·L^-1,and 16 mg·L^-1,the proportion of selenium content in fruit vacuoles and soluble components was higher than that of the treatment without AMF;the proportion of selenium content in the cell wall of the root was higher than that of the treatment without AMF,but the selenium content of vacuoles and soluble components The ratio was lower than that of the non-inoculated AMF treatment.（5）As the selenium concentration increased without AMF inoculation,the content of organic selenium in each part of the pepper increased.When the selenium concentration was 8 mg·L^-1,the content of organic selenium in each part of the pepper was higher with AMF inoculation compared to without.With increasing selenium concentration,the conversion rate of organic selenium in leaves gradually decreased,while the conversion rate of organic selenium in roots,stems,and fruits first increased and then decreased.At selenium concentrations of 2 mg·L^-1,4 mg·L^-1,and 8 mg·L^-1,the conversion rate of organic selenium in roots was lower without AMF inoculation,but significantly improved with AMF inoculation.After inoculation with AMF,compared with the uninoculated treatment,the organic selenium conversion rate of leaves and fruits decreased when the selenium concentration was 2 mg·L^-1,and the organic selenium conversion rate of leaves increased significantly when the selenium concentration was 16 mg·L^-1.By comparing the activities of enzymes in selenium metabolism,it was found that with increasing selenium concentration,the activities of ATPS（Adenosine sulfatase triphosphate）and APR（Adenylate sulfate reductase）first increased and then decreased,while the activity of SMT（Selenocysteine methyltransferase）gradually decreased.After inoculation with AMF,the activities of ATPS and APR increased compared to without AMF inoculation at the same selenium concentration,while SMT activity was reduced.In summary,after AMF inoculation,when the selenium concentration was 8 mg·L^-1,the yield per plant,plant height,stem diameter,fruit transverse and longitudinal diameter,root length,total phenols,total flavonoids,vitamin C,capsaicin and the antioxidant capacity is the highest.The accumulation of selenium in fruits was also highest at this concentration.After inoculation with AMF,compared with the uninoculated treatment,the proportion of selenium content in cell walls of roots,stems and leaves increased,and the proportion of fruit vacuoles and soluble selenium increased.The content of selenium in each part of the plant increased,and the activities of ATPS and APR also increased.In addition,the organic selenium content of pepper fruits increased after inoculation with AMF.