Biogeographic Controls of Tree Species Physiological Responses to Climate Warming: A Test with the Genus Quercus

Abstract:

Tree species responses to climate remain challenging to predict. However, tree species with larger range sizes are generally predicted to cope better with warming than species with smaller range sizes based on the expectation that range size is positively correlated with environmental tolerance or acclimation capacity. Here, we tested whether range size is predictive of tree species acclimation capacity by growing seedlings of climatically similar populations of ten Quercus (oak) species of varying range size (~78,500 km² to 1.1 million km²) under ambient conditions and passive warming (mean daily air temperature +2°C, maximum daily air temperature +5°C) over a four-month period. Carbon dioxide (CO₂) response curves and dark respiration measurements were taken at common temperatures (30°C and 25°C, respectively) at three different time points. The maximum rate of Rubisco carboxylation (V_cmax), the maximum rate of electron transport (J_max), and the photosynthetic rate at 400 ppm ambient CO₂ (A₄₀₀) were derived from the CO₂ response curves. Height and diameter measurements, as well as phenology surveys, were taken over the course this study to monitor growth of the seedlings and development of leaves. We found that Quercus species varied in their photosynthetic and respiratory responses to warming and range size was a poor predictor of species’ thermal acclimation responses. Instead, our results indicate that other factors, such as species climatic niche/distribution, leaf traits, or phylogenetic relatedness are better predictors of species responses to climate warming.