Can leaf net photosynthesis acclimate to rising and more variable temperatures?

Under future climates, leaf temperature (T_l) will be higher and more variable. This will affect plant carbon (C) balance because photosynthesis and respiration both respond to short-term (subdaily) fluctuations in T_l and acclimate in the longer term (days to months). This study asks the question: To what extent can the potential and speed of photosynthetic acclimation buffer leaf C gain from rising and increasing variable T_l? We quantified how increases in the mean and variability of growth temperature affect leaf performance (mean net CO₂ assimilation rates, A_net; its variability; and time under near-optimal photosynthetic conditions), as mediated by thermal acclimation. To this aim, the probability distribution of A_net was obtained by combining a probabilistic description of short- and long-term changes in T_l with data on A_net responses to these changes, encompassing 75 genera and 111 species, including both C3 and C4 species. Our results show that (a) expected increases in T_l variability will decrease mean A_net and increase its variability, whereas the effects of higher mean T_l depend on species and initial T_l, and (b) acclimation reduces the effects of leaf warming, maintaining A_net at >80% of its maximum under most thermal regimes.