Exogenous silicon alleviates drought stress in maize by improving growth, photosynthetic and antioxidant metabolism

Extreme dry weather caused by global climate change will reduce the growth and yield of plant crops. Silicon (Si) can improve plant growth and the resistance to various stresses. However, its effects on maize drought stress of the jointing and tasseling stages are unclear in the field. Therefore, the present study was carried out to investigate the effect of growth, photosynthetic and antioxidant metabolism on maize under moderate and severe drought stress with or without Si application (5, 15, 25 g·L−1) in the large farmland moisture control test field. Drought stress down-regulated plant height growth rate (25.80% ~ 39.11%), shoot dry weight (40.42%~68.97%), root dry weight (31.34% ~ 57.96%) and yield (14.51% ~ 36.52%) in the both stages, respectively. With the increase of drought stress, actual photochemical efficiency of PSⅡ (ΦPSⅡ), maximum photochemical efficiency of PSⅡ (Fv/Fm) and photochemical quenching (qP) decreased at different degrees while the non-photochemical quenching (NPQ) increased. One-to-twofold increase was observed in the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) in the drought-stressed conditions. Exogenous Si alleviated drought stress to a certain extent of damage, enhanced plant growth, photosynthetic pigment contents, chlorophyll fluorescence parameters, gas exchange parameters, photosynthetic enzymes activity, the stomatal size and stomatal aperture, inhibited the increase in the superoxide free radical ion (O2·−) production rate, hydrogen peroxide (H2O2), malondialdehyde (MDA) and electrolyte leakage (EL), and further increased the key antioxidant enzymes activities and the osmotic regulatory substance contents. The activities of monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR), and the contents of ascorbate (AsA) and glutathione (GSH) increased, and the contents of dehydroascorbate (DHA) and oxidized glutathione (GSSG) declined by Si application in both stages. Therefore, exogenous Si could decrease maize oxidative stress response in drought-stressed by strengthening the antioxidant defense system and photosynthetic metabolism, improving the AsA-GSH cycle, increasing osmotic substance contents, as well as playing a vital role in improving the drought resistance of maize. Overall, the external use of Si ameliorated growth, photosynthetic and antioxidant metabolism under drought stress.