Objectives Phosphorus (P) plays an important role in stress tolerance of rice. We studied the effect of phosphorus supply levels on rice photosynthetic efficiency, nutrient absorption and growth, to find nutrient management for the adaptation of rice production to climate change.

Methods A pot experiment was conducted using rice cultivar ‘Lingliangyou 268’, an indica two-series hybrid rice, as test material. Two growth temperature conditions were provided, one was the local ambient temperature (aT), and the other was 1.5℃ elevated temperature (eT) by infrared heater (MR-2420) above the rice plants. Under each air condition, five P₂O₅ application rates of 0, 30, 60, 90 and 120 mg/kg were setup, denoted as P₀, P₃₀, P₆₀, P₉₀ and P₁₂₀. Leaf photosynthetic characteristics parameters, nutrient content and biomass were measured at the rice jointing stage.

Results The net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), and intercellular CO₂ concentration (C_i) of rice leaves were all maximized, except for the minimum value of C_i in P₉₀ treatment under ambient condition. Compared to aT in the same P application rate, eT significantly increased G_s and T_r in P₀, P₃₀, and P₆₀ treatments, did not on G_s in P₉₀ and T_r in P₁₂₀ treatment. eT increased shoot P content in P₉₀ and P₁₂₀ treatments and root P content in P₀ and P₁₂₀ treatments, enhanced shoot and root N content in P₆₀ and P₉₀ treatments, elevated shoot K content in P₃₀ treatment but did not significantly affect root K content. Under both aT and eT condition, the highest shoot, root and total biomass of rice were appeared in P₉₀, which were significantly higher than in the other treatments. In the same P application rate, eT increased the root biomass in P₃₀ and P₆₀, decreased shoot biomass in all the P treatments and total biomass in P₀ and P₉₀ treatments. The results of the pathway analysis showed that under aT conditions, the greatest influence of rice biomass was photosynthesis (P_n=0.554), followed by P and N uptake, and the influence of N and P was direct, with the pathway coefficients of 0.309 and 0.308, respectively. Under eT condition, the greatest influence of rice biomass was P (P_TP=0.794), followed by N and photosynthesis, and the two had indirect effects through P, with the indirect pathway coefficients of 0.547 and 0.528, respectively.

Conclusions Suitable P application rate is the key factor for maintaining high photosynthetic efficiency and biomass of rice. In the rice production of Jiangsu Province, applying 110 kg/hm² of P fertilizer could achieve high photosynthetic efficiency, nutrient uptake and biomass of rice, enhance the tolerance to climate warming by keeping or increase root biomass at jointing stage of rice, and lay the foundation for rice production in the later stages of the season. Therefore, maintaining a reasonable and stable level of phosphorus application is an effective measure for rice to withstand the adverse effects of climate warming.