Decadal rice cultivation reconfigured saline-alkali paddy nitrogen cycling through microbial-DNRA dominance and soil amelioration synergy

Abstract

Long-term rice cultivation shows potential in alleviating soil salinization, yet the mechanistic links between sustained cultivation and optimized nitrogen cycling in saline-alkali paddies remain unclear. Here, we integrated a field chronosequence experiment (0–20 years) with a global meta-analysis of saline-alkali agroecosystems to elucidate the spatiotemporal drivers of soil nitrogen dynamics. Field data revealed decadal organic inputs elevated total nitrogen (TN) by 80.77 % (p < 0.01), while meta-regression confirmed that TN and available nitrogen (AN) exhibited linear accumulation over decades of rice cultivation. Microbial communities exhibited directional succession patterns, with phylogenetic assembly strongly correlated to nitrogen stoichiometry and narGH/nirS/nirB/nxrAB gene abundance. Metagenomic reconstruction and meta-network analysis convergently identified microstructure optimization and substrate sufficiency as key factors associated with soil dissimilatory nitrate reduction to ammonium (DNRA), denitrification, and complete ammonia oxidation processes. Crucially, inferred convergence at 10 years of cultivation marked the critical juncture where salinization alleviation converged with microbial modularity to maximize nitrogen use efficiency. This work pioneers a soil-microbe-metabolic coevolution framework validated by field-meta synergy, establishing operational chronosequence thresholds for sustainable saline-alkali paddy management. By coupling mechanistic experiments with global meta-analytical evidence, our work advances predictive understanding of nutrient-cycling recovery in marginal lands.