Mitigating water stress impacts on corn plants using microbial-based biostimulants and organic amendments

Water stress is one of the main factors limiting crop productivity in arid and semi-arid Mediterranean regions. The aim of this study is to assess the effect of using organic amendments (C) alone or combined with biostimulants based on arbuscular mycorrhizal fungi (F) and plant growth-promoting bacteria (B) on Zea mays L. in alleviating the effects of water stress. Two factors were studied in this work: the water regime (25% and 75% of field capacity) and the single, double and triple application of F, B and C. Shoot and root dry biomass, osmolyte content (proline and total soluble sugars), antioxidant system (Polyphenol oxidase), stress marker content (malondialdehyde and hydrogen peroxide) and mycorrhization intensity and frequency were assessed. The results showed that drought stress negatively affected plant biomass, biochemistry, and root colonization by arbuscular mycorrhizal fungi. In addition, combined applications, particularly mycorrhizae and compost, improved shoot and root dry biomass by 179 and 275%, respectively, compared with untreated drought-stressed plants. Mycorrhization intensity and frequency were higher when the soil contained plant growth-promoting bacteria and reduced when amended with compost alone under water stress. The single or combined application of F, B and C enhanced proline and total soluble sugar content and polyphenol oxidase activity in leaves in comparison with untreated plants. On the other hand, malondialdehyde and hydrogen peroxide content were minimized (67% and 18%, respectively) by applying the triple combination of F, B and C. In conclusion, the strategy of combining organic amendments and microbial-based biostimulants may offer an environmentally friendly solution in arid and semi-arid regions where soils are degraded to provide drought protection for corn crops.