Relationships between C/N metabolism and rice growth related indicators under alternating drought and flooding stress

The increasing frequency of drought and flooding events due to climate change exposes rice to intensified alternating drought and flooding stress during different growth stages. To elucidate the impacts of alternating drought and flooding stress on rice growth and carbon (C) and nitrogen (N) metabolism, five irrigation regimes were established: alternating cycle of light drought-flooding-light drought during the tillering stage (T-LD), heavy drought-flooding-heavy drought during the tillering stage (T-HD), light drought-flooding-light drought during the jointing stage (J-LD), heavy drought-flooding-heavy drought during the jointing stage (J-HD), and frequent irrigation with shallow water depth (0–5 cm) for growth stages except for the maturation stage (CK). The results indicated that the tiller numbers, K⁺ concentrations in leaves, and above-ground biomass subjected to T-HD and T-LD treatments were significantly lower than in CK, J-HD and J-LD. Compared to CK, T-LD enhanced chlorophyll content and nitrate reductase activity (NRA) in rice leaves, leading to elevated photosynthetic rates (P_n) and improved δ¹³C values. The δ¹⁵N values under the CK, T-HD, and T-LD treatments were significantly greater than those under the J-HD and J-LD treatments (p<0.05). Additionally, NRA showed a significant positive correlation with leaf N concentration during the jointing stage. Path analysis indicates that δ¹³C, leaf water content, tiller number, leaf area, K⁺ concentration, and N concentration were directly related to above-ground biomass, whereas photosynthetic parameters indirectly affected biomass through N-metabolism related indicators. This result offers a theoretical support for the scheduling of irrigation and drainage practices in the field.