Increasing corn compensatory growth upon post-drought rewatering using ammonia-oxidising bacterial strain inoculation

Abstract

This study explored the effects of ammonia oxidizing bacterial (AOB) strain S2_7_25 on the compensatory growth of corn (Zea mays L.) upon post-drought rewatering using seedlings as test materials. This study consisted of two treatment conditions: isolation and screening of AOB strain and AOB strain inoculated to soils. Isolated and screened from soil, S2_7_25 had 100% similarity to Acinetobacter pittii. The experimental design of S2_7_25 inoculation to soils was composed of five treatments: (1) wetness, (2) post-drought rewatering, (3) post-drought rewatering with S2_7_25 inoculation, (4) post-drought rewatering with nitrification inhibitor addition to soil and (5) post-drought rewatering with nitrification inhibitor addition to soil and S2_7_25 inoculation. Rewatering increased the total biomass and net photosynthetic rate of corn compared with wetness, and S2_7_25 inoculation greatly increased these parameters of rewatering corn. However, nitrification inhibitor addition greatly decreased these parameters of rewatering corn inoculated with or without S2_7_25. Rewatering increased the rhizosphere soil nitrification rate of corn, and rewatering with S2_7_25 inoculation further increased it. However, nitrification inhibitor addition decreased this parameter in rewatering corn with or without S2_7_25 inoculation. The cytokinin delivery rates from the roots to the leaves were regulated by soil nitrification in the rhizosphere, and it determined the leaf cytokinin concentration that is closely related to corn rewatering growth. The highest leaf cytokinin concentration during rewatering caused over-compensatory growth and the highest water use efficiency in rewatering corn with S2_7_25 inoculation among all treatments. Compensatory and under-compensatory growth occurred in rewatering corn and in corn with nitrification inhibitor addition, respectively. In a word, S2_7_25 increased corn compensatory growth by regulating soil nitrification and root-induced leaf cytokinin.