Selenium inorganic sources applied to soil: Effects on gas exchange and anatomical changes of radishes

Selenium (Se), in low doses, provides several beneficial effects, such as plant resistance to various abiotic stresses (e.g. drought stress and low/high temperatures). However, Se excess causes toxicity, with harmful impacts such as a decline in yield. Here, we studied the effects of fertilization with different Se sources and doses applied via soil on Se accumulation, toxicity, as well as on gas exchange, and anatomy of leaves and roots of radish plants. A randomized experimental design was adopted with three replications in a 2 × 3 + 1 factorial arrangement: two Se sources (sodium selenate – Na2SeO4 and sodium selenite – Na2SeO3·5H2O), three Se doses applied on soil (0.6, 1.2, and 1.8 mg dm−3), and one control treatment (without Se application). Each experimental unit consisted of one pot containing six radish plants. Selenate at 1.8 mg Se dm−3 increased the Se accumulation and radish dry matter. Selenite generally caused significant changes in the anatomical part, mainly in the conductive tissues of the leaves. In leaves with selenite fertilization, it was estimated that the maximum Se accumulation would be 5.9 µg plant−1 with a rate of 2.0 mg Se dm−3. However, it was impossible to estimate the maximum Se accumulation with selenate fertilization because as the dose increased, there were also increases in accumulation, thus presenting a linear regression. The maximum Se accumulation in radishes would be 10.7 µg Se plant −1 with 1.2 mg Se dm−3 by selenite and 45.8 µg Se plant−1 with 5.0 mg Se dm−3 by selenate. Although the highest dry mass production occurred with the 1.8 mg Se dm−3 through selenite, it is recommended to use smaller doses to provide adequate Se consumption selenate. The gas exchange and the anatomy of the plants changed due to Se fertilization through selenate and selenite.