LAUSR

BACKGROUND AND AIMS Increased plant photosynthesis under nocturnal warming is a negative feedback mechanism to overcompensate for nighttime carbon loss to mitigate climate warming. This photosynthetic overcompensation effect has been observed in dry deciduous ecosystems but whether it exists in subtropical wet forest trees is unclear. METHODS Two subtropical evergreen tree species (Schima superba and Castanopsis sclerophylla) were grown in a greenhouse and exposed to ambient and elevated nighttime temperature. The occurrence of the photosynthetic overcompensation effect was determined by measuring daytime and nighttime leaf gas exchange and nonstructural carbohydrates (NSC) concentration. KEY RESULTS A reduction in leaf photosynthesis for both species and an absence of persistent photosynthetic overcompensation were observed. The photosynthetic overcompensation effect was transient in S. superba due to respiratory acclimation and stomatal limitation. For S. superba, nocturnal warming resulted in insufficient changes in nighttime respiration and NSC concentration to stimulate overcompensation and inhibited leaf stomatal conductance by increasing the leaf to air vapor pressure deficit. CONCLUSIONS The results indicate that leaf stomatal conductance is important for the photosynthetic overcompensation effect in different tree species. The photosynthetic overcompensation effect under nocturnal warming may be a transient occurrence rather than a persistent mechanism in subtropical forest ecosystems.