Thermal regulation shapes the coordination of stomatal conductance, transpiration, and photosynthesis in rice.

Heat-stress driven by global warming alters rice (Oryza sativa) water-use dynamics. To assess adaptive water-use strategies under elevated air temperature, we conducted a three-year whole-season experiment in natural light climate chambers with ambient, +1 °C, +2 °C, and +5 °C warming treatments. Stomatal conductance (gs), transpiration rate (E), net photosynthetic rate (An) and leaf developmental dynamics were continuously measured across growth stages. Above the photosynthetic optimum leaf temperature (Tleaf-opt-An = 30.8 °C), An declined while gs increased. The increase in gs accelerated beyond a critical threshold (Tleaf-crit = 34.2). This stomatal-photosynthetic decoupling was associated with enhanced transpiration and evaporative cooling. During the reproductive stage, heat stress constrained grain-filling sink capacity and delayed leaf senescence, sustaining higher An, gs and E. Rice exhibits heat-induced shifts in the coordination among carbon assimilation, stomatal behaviour, and water use, while source-sink dynamics under heat-stress further modulated carbon assimilation and water consumption. Incorporating these mechanisms into land surface models is essential for more reliable predictions under global warming scenarios.