Mechanisms underlying leaf photosynthetic acclimation to warming and elevated CO2 as inferred from least‐cost optimality theory

The mechanisms responsible for photosynthetic acclimation are not well understood, effectively limiting predictability under future conditions. Least‐cost optimality theory can be used to predict the acclimation of photosynthetic capacity based on the assumption that plants maximize carbon uptake while minimizing the associated costs. Here, we use this theory as a null model in combination with multiple datasets of C3 plant photosynthetic traits to elucidate the mechanisms underlying photosynthetic acclimation to elevated temperature and carbon dioxide (CO2). The model‐data comparison showed that leaves decrease the ratio of the maximum rate of electron transport to the maximum rate of Rubisco carboxylation (Jmax/Vcmax) under higher temperatures. The comparison also indicated that resources used for Rubisco and electron transport are reduced under both elevated temperature and CO2. Finally, our analysis suggested that plants underinvest in electron transport relative to carboxylation under elevated CO2, limiting potential leaf‐level photosynthesis under future CO2 concentrations. Altogether, our results show that acclimation to temperature and CO2 is primarily related to resource conservation at the leaf level. Under future, warmer, high CO2 conditions, plants are therefore likely to use less nutrients for leaf‐level photosynthesis, which may impact whole‐plant to ecosystem functioning. We use least‐cost optimality theory to explore the mechanisms of photosynthetic acclimation to temperature and carbon dioxide (CO2). The comparison of the theory to data found that plants downregulate their biochemistry in response to elevated temperature and CO2 to avoid excess resource use. While the temperature response tended to follow theoretical expectations, the CO2 response indicated that plants may become more electron transport rate‐limited under high CO2. Together, our findings indicate that future projected increases in temperature and CO2 will reduce nutrient use to support photosynthesis, which may impact ecosystem‐scale processes.