Attributing the temperature response of tree seedling growth to underlying mechanisms

Studies of plant responses to temperature often focus on rates photosynthesis and respiration. However, within-plant utilisation and allocation of carbon are also strongly affected. It is unclear how much each of these processes contribute to determining the overall temperature response of growth. We applied a data assimilation framework to a glasshouse experiment with detailed physiological and growth measurements to investigate the relative contribution of different physiological processes to the overall temperature response of tree seedling growth. We found that both short-term effects of temperature and acclimatory responses of photosynthesis and respiration had a significant impact on the temperature response of growth. However, the effect of temperature on biomass allocation patterns to different tissues, non-structural carbohydrate utilisation and C losses to other unmeasured losses were also substantial in determining the temperature response of growth, particularly at sub-optimal temperatures. Our work demonstrates that the growth response to warming cannot be predicted using only the direct effect of temperature on photosynthesis and respiration and emphasizes the importance of temperature acclimation of photosynthesis, respiration and other C balance processes. Our results provide new guidance for process-based models to correctly describe the temperature effects on tree growth.