The role of a foliar nitrogen allocation strategy in controlling the CO₂ fertilization effect in rice

Abstract

Elevated atmospheric carbon dioxide (eCO₂) concentration generally boosts the photosynthetic rate of rice and tends to reduce the concentration of foliar nitrogen (N). However, there is limited evidence concerning how this shift in N allocation affects the plant's overall response to eCO₂. Therefore, this study integrated data from free-air CO₂ enhancement (FACE) experiments, open-top chamber (OTC) experiments, meta-analysis, and pot experiments with N fertilizer gradients to comprehensively investigate the physiological mechanisms of the rice CO₂ fertilization effect (CFE) and its intrinsic relationship with leaf N allocation strategy. Results showed that eCO₂ significantly enhanced rice carbon sequestration but led to reduced N allocation in the carboxylation system (PN_cb) and electron transport components (PN_et). The established least-squares regression model indicated that PN_cb and PN_et jointly control CFE (R² ​= ​0.73). Additionally, a global meta-analysis further confirmed the global applicability of the model (R² ​= ​0.75). The N addition gradient experiment revealed that higher N levels significantly alleviated the negative impacts of PN_cb and PN_et constraints on the CFE. Structural equation modeling (SEM) analysis showed that N fertilizer application indirectly influenced CFE by regulating PN_cb (path coefficient of 0.74) and PN_et (path coefficient of 0.80), with the role of N allocation strategies being significantly stronger than the direct effect of N fertilizer (path coefficient of 0.49). These findings highlight the critical role of the foliar N allocation strategy in CFE. This study broadens our understanding of the synergistic regulation mechanisms between carbon and N in crops.

Keywords

Carboxylation system / CO₂ fertilization effect / Electron transport system / Foliar nitrogen / Photosynthesis / Rice

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