Associate Professor Auburn University Auburn, Alabama, United States
Abstract: Many plants acclimate to seasonal or spatial variation in growth temperature by modifying the short-term temperature sensitivity of physiological processes. At the plant-scale, ‘thermal acclimation’ is thought to optimize carbon uptake and use. At larger-scales, thermal acclimation can reduce the positive feedback between temperature and CO2. However, questions remain about the influence of resource availability on thermal acclimation responses in species with different functional strategies and ecological niches, and whether thermal acclimation responses are similar in different plant tissues. Here, we investigated thermal acclimation of leaf and stem respiration (R) in 11 different tree species native to the southeastern U.S. growing together outdoors under different water and nutrient regimes. We hypothesized that water and nutrient availability will influence thermal acclimation of R in all species, and leaves would show stronger acclimation responses than stems. All species showed evidence of thermal acclimation of leaf R. However, thermal acclimation of leaf R in individual species was dependent upon resource availability. Stems only showed thermal acclimation of respiration when analyzed monthly and not when evaluated over the entire growing season. Instead, we found that stem respiration rates decreased as growth slowed, indicating that stems have a lower energy requirement during later stages of plant growth, with consequent decreases in respiration rate. We conclude that the influence of growth rate on stem respiration overwhelms the influence of possible temperature acclimation. Our results indicate that thermal acclimation of plant respiration varies between tissue types, with leaves showing greater respiratory thermal acclimation than stems. Furthermore, the variability of the growing season should be taken into account when studying thermal acclimation of plant stem respiration. These results have implications for predicting aboveground plant respiration of diverse species across resource availability gradients, and across different growth temperatures.
