Dark respiration explains nocturnal stomatal conductance in rice regardless of drought and nutrient stress

Abstract

The ecological mechanism underlying nocturnal stomatal conductance (g(sn)) in C-3 and C-4 plants remains elusive. In this study, we proposed a 'coordinated leaf trait' hypothesis to explain g(sn) in rice plants. We conducted an open-field experiment by applying drought, nutrient stress and the combined drought-nutrient stress. We found that g(sn) was neither strongly reduced by drought nor consistently increased by nutrient stress. With the aforementioned multiple abiotic stressors considered as random effects, g(sn) exhibited a strong positive correlation with dark respiration (R-n). Notably, g(sn) primed early morning (5:00-7:00) photosynthesis through faster stomatal response time. This photosynthesis priming effect diminished after mid-morning (9:00). Leaves were cooled by g(sn)-derived transpiration. However, our results clearly suggest that evaporative cooling did not reduce dark respiration cost. Our results indicate that gsn is more closely related to carbon respiration and assimilation than water and nutrient availability, and that dark respiration can explain considerable variation of g(sn).