Integrated Mechanisms of Soil–Plant System Resilience to Drought–Flood Abrupt Alternation in Maize

Drought–flood abrupt alternation is a frequent compound stress under climate change, threatening crop production. However, how crops integrate soil, root and leaf signals for systemic adaptation remains unclear. Maize was subjected to different drought intensities (mild, moderate and severe) followed by flooding durations (3 and 6 days), with three biological replicates per treatment. Soil properties, enzyme activities, rhizosphere microbiomes, root metabolites, leaf hormones and organ C/N were measured and integrated using multivariate analyses. The stress significantly inhibited aboveground biomass, with drought and flooding exhibiting strong interactions. At the soil level, moderate drought pretreatment buffered nitrate depletion and redox decline, whereas prolonged flooding promoted ammonium accumulation. Under moderate drought followed by prolonged flooding, soil organic carbon and acid phosphatase were synergistically enhanced. At the plant level, short‐term flooding after mild drought activated root fermentation. Carbon and nitrogen allocation decoupled, with prolonged flooding after moderate drought producing “root high‐C/low‐N” versus “leaf high‐N” patterns. Hormone responses formed stress‐specific codes: prolonged flooding activated salicylic acid, whereas mild drought followed by prolonged flooding induced abscisic acid. At the system level, network and path analyses identified leaf‐derived anthranilic acid as a node linking soil redox status with leaf carbon metabolism. Rhizosphere communities underwent selection by prior drought, exhibiting succession from aerobic decomposers to anaerobic respirers and stress‐tolerant actinomycetes. Crop responses constitute a multi‐level coupled process initiated by soil conditions, modulated by rhizosphere microbiota, and integrated through plant metabolic and signalling networks. This study suggests several potential regulatory targets—moderate drought priming, microbial legacy effects, organ‐specific C/N allocation and anthranilic acid‐mediated signalling—providing a hypothesis‐generating framework for further investigation into optimizing irrigation scheduling and designing water management strategies to enhance crop resilience under climate fluctuations.