Global patterns of the responses of leaf-level photosynthesis and respiration in terrestrial plants to experimental warming

Aims The balance between leaf photosynthesis and respiration of terrestrial plants determines the net carbon (C) gain by vegetation and consequently is important to climate-C cycle feedback. This study is to reveal the global patterns of the responses of leaf-level net photosynthesis and dark respiration to elevated temperature. Methods Data for leaf-level net photosynthesis rate (P-n) and dark respiration rate (R-d) in natural terrestrial plant species with standard deviation (or standard error or confidence interval) and sample size were collected from searched literatures on Web of Science. Then a meta-analysis was conducted to estimate the effects of experimental warming on leaf-level P-n and R-d of terrestrial plants. Important findings Across all the plants included in the analysis, warming enhanced P-n and R-d significantly by 6.13 and 33.14%, respectively. However, the responses were plant functional type (PFT) specific. Specifically, photosynthesis of C-4 herbs responded to experimental warming positively but that of C-3 herbs did not, whereas their respiratory responses were similar, suggesting C-4 plants would benefit more from warming. The photosynthetic response declined linearly with increasing ambient temperature. The respiratory responses linearly enhanced with the increase in warming magnitude. In addition, a thermal acclimation of R-d, instead of P-n, was observed. Although greater proportion of fixed C was consumed (greater R-d/P-n ratio), warming significantly enhanced the daily net C balance at the leaf level. This provides an important mechanism for the positive responses of plant biomass and net primary productivity to warming. Overall, the findings, including the contrastive responses of different PFTs and the enhancement in daily leaf net C balance, are important for improving model projection of the climate-C cycle feedback.