Biomass allocation, nutrient uptake, and stoichiometric responses of rice under alternate wetting and drying and fertilization regimes

Abstract Under the pressing issue of water scarcity, water-saving irrigation and fertilizer management are widely promoted to improve sustainability in rice cultivation. However, the mechanisms underlying rice phenotypic plasticity remain poorly understood. This study investigated biomass allocation, nutrient stoichiometry, and trait allometry in rice under continuous flooding (CF) and alternate wetting and drying (AWD) treatments, combined with six fertilization regimes. AWD increased root length, root dry weight, and root–shoot ratio, indicating a shift toward belowground allocation. Plant stoichiometry was correlated with phosphorus-related ratios, with a positive relationship between C:P and N:P and a negative relationship with phosphorus uptake. Root length showed positive plasticity across all fertilization regimes (PP = 0.091–0.294), whereas root dry weight and root–shoot ratio reached their highest responses under N50, N75M, and N50MB (PP up to 0.469). Plasticity related to biomass accumulation, nutrient uptake, and stoichiometric regulation varied among fertilization treatments, with N75M and N50MB tending to support positive biomass responses. Path analysis identified root allocation as the primary AWD-responsive trait and nutrient uptake as the strongest predictor of biomass production. These results suggest that rice responses to water-saving irrigation are primarily expressed through biomass reallocation toward roots, while plant stoichiometry remains comparatively buffered.