Enhancing growth and transpiration efficiency of corn plants with compost addition and potential beneficial microbes under well-watered and water-stressed conditions

Abstract Background and aims Water scarcity due to increasing climate variability means improved drought tolerance in crop plants is more urgent. Addition of organic wastes could enhance crop drought tolerance through improved nutrition or increased soil water holding capacity. However, their effect on crop water relations, mediated by plant beneficial soil microbes, remains less well-studied. This study aims to understand how applications of nutrient-rich composts affect the growth and transpiration use efficiency (TE), the ratio of shoot biomass to total transpiration, of corn plants under well-watered and water-stressed conditions. Methods The study used a factorial combination of four amendment treatments (surface applied fertilizer, surface-and deep-banded compost, and deep-banded compost with biochar) with two water regimes. Results All compost treatments, irrespective of whether they were applied to the topsoil or subsoil, alone or with biochar, increased TE of corn plants by ~ 10%, relative to surface fertilizer. Compost addition reduced average stomatal conductance and transpiration rate by > 30%, which could be attributed to elevated leaf hormone concentrations of abscisic acid and methyl jasmonate. Furthermore, compost addition increased the abundance of soil fungi and bacteria in the Bacillus and Streptomyces genera, which are known to increase the biosynthesis of leaf hormones. In the deep compost treatments, corn plants exhibited significantly higher root length densities in subsoil layers, resulting in increased subsoil water extraction. Conclusion Greater biomass production following deep compost addition under water stress was mainly attributed to microbially mediated increase in TE, followed by improved deep root growth and water uptake from the subsoil layer.