Roles and underlying mechanisms of foliar selenium application in regulating growth of <i>Codonopsis tangshen</i>

To explore the effects of foliar selenium(Se) application on the growth and nutritional quality of Codonopsis tangshen and elucidate the mechanisms underlying plant response to supplementation with selenium, a field experiment with six treatments(0, 25, 50, 100, 200 and 400 g·hm-2 Se in sodium selenite) was conducted to determine the effects of different Se treatments on root morphology, yield, quality, Se speciation and partial rhizospheric soil nutrients of C. tangshen. Compared with the control, application of appropriate foliar Se increased root diameter, crop yield, and polysaccharide and lobetyolin content of C. tangshen. Differences between Se treatments and control were statistically significant at the concentration of 200 g · hm-2 Se. Selenium in C. tangshen mainly existed in the form of organic Se(>70% of total Se), and the proportion of organic Se initially increased and then decreased with increasing foliar Se. The maximum value of organic Se was 83.6% when the foliar Se level was 200 g·hm-2. The Se treatments promoted the growth of C. tangshen under Se level of 25~400 g·hm-2; however, the promotion effects firstly increased and then decreased with the increasing foliar Se level. Significant differences of rhizospheric soil nutrients among different Se treatments were observed:The 100 g · hm-2 and 200 g · hm-2 Se treatments significantly increased the rhizospheric soil alkali-hydrolyzed nitrogen and available potassium content of C. tangshen, compared with the control. Pearson analysis and redundancy analysis showed that the change of nutrient content in rhizosphere soil might be an important factor affecting the growth of C. tangshen. In conclusion, C. tangshen was a good candidate for Se supplementation and spraying 100~200 g · hm-2 Se in the bud and flowering stage could increase the yield, polysaccharide, lobetyolin and Se content of C. tangshen, thereby promoting the development of Se-enriched C. tangshen products