Mechanism of silicon application on improving physiological functionand tolerance to selenium of upland rice

Objectives The effects of silicon (Si) application on leaf surface silicified cell structure, and the antioxidant substance contents of upland rice were studied, to explore the mechanism of Si fertilization in improving the selenium (Se) absorption and rice yield and quality, and provide technique support for cultivation ofSe-rich upland rice in arid regions.

Methods A upland rice field experiment was carried out in Shihezi, Xinjiang. The treatments were composed of basal Se fertilizer 0 and 7.2 kg/hm² (Se0, Se), and basal Si fertilizer 0, 250, and 500 kg/hm² (Si0, Si250, and Si500), totaling 6 treatments, taking analytically pure sodium silicate and sodium selenite as Si and Se fertilizers. At tillering, booting, full-heading, and filling stage, leaf chlorophyll values (SPAD) were monitored, leaf and root samples were collected for measurement of malondialdehyde (MDA) and antioxidant substances. At full-heading stage, leaf soluble protein, soluble sugar, and non-enzymatic antioxidant substances were measured, and leaf surface microstructure was observed. The grain Se content, yield, and quality indexes were analyzed at maturing stage of upland rice.

Results Si application arranged the loose silicified cells more orderly and formed gradient silica bodies, thereby enhancing mechanical strength of the leaf tissues. Compared to Si0, Si application significantly increased leaf stomatal aperture and SPAD values, with SPAD increment of 10.9%−16.9% in Si500 treatment. Se application reduced MDA content by 15.6%−18.2% in leaf and 16.9%−18.0% in root, but increased soluble protein content by 16.5%−18.6% compared to Se0. Si improved activities of superoxide dismutase (SOD) by 14.2%−20.9% at various growth stages, respectively, improved activities of peroxidase (POD), catalase (CAT) at tillering, booting, and heading stage by 14.7%−30.4% and 27.8%−52.6%, respectively compared to Si0. Compared with Si0, Si application under Se condition increased leaf SOD, POD and CAT activities by 8.1%−8.9%, 5.3%−8.8%, 7.9%−16.4%; Si250 increased the ascorbic acid (AsA) and glutathione (GSH) contents by 18.3% and 25.2%. Si application significantly promoted Se absorption by upland rice. The grain Se content under Si250+Se treatment was 150.0% and 21.1% higher than Si250+Se0, and that under Si500+Se was 250.0% and 23.8% higher than Si500+Se0; Si250+Se and Si500+Se treatments increased the 1000-grain weight and grain filling rate by 6.4%, 6.9%, and 7.9%, 10.8%, respectively, resulting in the yield increase by 14.8% and 16.5%, compared to Si250+Se0 and Si500+Se0, respectively. Si application enhanced the milled rice and whole-head grain rate, decreased chalkiness rate, increased viscosity, decreased amylose content, thus improving the taste and palatability of upland rice significantly.

Conclusions Si application could improve the surface structure and mechanical strength of upland rice leaves, increase stomatal area and aperture, and increase and prolong the function of leaves, thereby improve the yield and quality of rice. In addition, Si application could maintain relatively high antioxidant enzyme activities, and ascorbic acid and glutathione contents in upland rice leaves, which could alleviate the Se toxicity and allow rice to accumulate high Se content. Comprehensively considering all the results, applying 250 kg/hm² sodium silicate and 7.2 kg/hm² sodium selenite is an effective combination for the efficient production of Se-enriched upland rice production.