Drivers of leaf carbon exchange capacity across biomes at the continental scale

Abstract

Realistic representations of plant carbon exchange processes are necessary to reliably simulate biosphere-atmosphere feedbacks. These processes are known to vary over time and space, though the drivers of the underlying rates are still widely debated in the literature. Here, we measured leaf carbon exchange in >500 individuals of 98 species from the Neotropics to high boreal biomes to determine the drivers of photosynthetic and dark respiration capacity. Covariate abiotic (long- and short-term climate) and biotic (plant type, plant size, ontogeny, water status) data were used to explore significant drivers of temperature-standardized leaf carbon exchange rates. Using model selection, we found the previous week's temperature and soil moisture at the time of measurement to be a better predictor of photosynthetic capacity than long-term climate, with the combination of high recent temperatures and low soil moisture tending to decrease photosynthetic capacity. Non-trees (annual and perennials) tended to have greater photosynthetic capacity than trees, and, within trees, adults tended to have greater photosynthetic capacity than juveniles, possibly as a result of differences in light availability. Dark respiration capacity was less responsive to the assessed drivers than photosynthetic capacity, with rates best predicted by multi-year average site temperature alone. Our results suggest that, across large spatial scales, photosynthetic capacity quickly adjusts to changing environmental conditions, namely light, temperature, and soil moisture. Respiratory capacity is more conservative and most responsive to longer-term conditions. Our results provide a framework for incorporating these processes into large-scale models and a data set to benchmark such models.

Acclimation of leaf respiration consistent with optimal photosynthetic capacity

“…Our results contradict this assumption, and provide a quantification of the temperature responses of both V cmax and R d that explicitly takes acclimation into account. Given that V cmax has been found to vary seasonally, and can be predicted using the temperature of the previous week (Smith & Dukes, ), a weekly to monthly acclimation time scale would be appropriate for LSMs to incorporate this process. It has also been shown that high growth temperature has a stronger negative impact on the instantaneous thermal response of V cmax than that of dark respiration (Smith & Dukes, ).…”

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

“…First, thermal acclimation of net CO 2 assimilation consists of several processes (changes in photosynthetic capacity, photorespiration, and respiration in the light, as well as changes in stomatal conductance; Kattge & Knorr, ; Slot & Kitajima, ; Yamori et al, ). These responses could occur at different time scales, although recent evidence suggests that photosynthetic capacity and respiration may respond at similar time scales (Smith & Dukes, ). The response function A net ( T l ) (Equation ), condenses all these physiological mechanisms via a set of measurable parameters (Equation ) and their changes with acclimation.…”

Global photosynthetic capacity is optimized to the environment

“…The applicability of the theory relies on knowledge of photosynthetic capacity, which varies both among species and over time and space, in response to environmental conditions (Ali et al . ; Smith & Dukes ).…”

“…In the majority of these models, C 3 photosynthesis is simulated using well-established biochemical theory (Farquhar et al 1980). The applicability of the theory relies on knowledge of photosynthetic capacity, which varies both among species and over time and space, in response to environmental conditions (Ali et al 2015;Smith & Dukes 2018).…”