Influence of UV exclusion and selenium on carbon fixation, nitrogen fixation and yield of soybean variety JS-335

Abstract

Ultraviolet-B (UV-B) is a significant abiotic stress factor exerting multiple effects on plant growth. This study was undertaken to unravel if selenium (Se), an element known to increase the stress tolerance, is able to defend soybean plants against detrimental effects of ambient UV. Soybean plants were grown in soil supplemented with Se at 0, 0.1 and 1.0mgkg−1 soil under ambient and filtered solar UV. The influence of ambient and filtered solar UV and of Se was determined on growth of above/below-ground parts, biomass accumulation, rate of photosynthesis, protein, nitrate reductase activity, leghemoglobin content and yield in soybean var. JS 335. Both the low and high Se dosage significantly enhanced the growth of above-ground parts (plant height, leaf area and total biomass accumulation) as well as the growth of below-ground parts (root length, root biomass, number of nodules and fresh weight of nodules) as compared to their control (0mgkg−1 soil) plants under ambient and filter control treatments (+UV-B and UV-A). Leghemoglobin content was higher in the root nodules and the total chlorophyll, total soluble protein and NR activity in leaves were also significantly increased by Se as compared to their controls under ambient and filter control treatments. Similarly, exclusion of solar UV radiations also significantly enhanced these parameters except NR activity as compared to the controls. Selenium increased the grain yield of soybean under ambient conditions. The results suggest that the increased yield of soybean by Se and UV exclusion was related to increased carbon and nitrogen fixation which was evident by the increased rate of photosynthesis, higher activity of nitrate reductase and high amount of leghemoglobin in root nodules of soybean. An increase in physiological indices with Se supply confirmed that Se plays a positive role in improving UV (280–400nm) tolerance of soybean seedlings. A comparison of results of growing plants in supplementation of Se in soil under ambient UV and without Se supplementation in soil under solar UV exclusion indicates a parallelism between the two effects. Both enhanced the growth of the plants and accumulation of biomass, hence enhanced fixation of carbon and nitrogen, ultimately enhanced the crop yield. Thus Se supply significantly increased the growth and yield of soybean under ambient UV stress.