PS 43-172 - Temperature Adaptation and Acclimation of Respiration in Related Pine Species and Populations of the Southern United States

Abstract: Warmer and more variable temperatures have the potential to alter the function and sustainability of pine forests in the southeastern United States, as well as the economic and ecological benefits they provide. Tree responses to temperature variability are likely to differ among pine species and populations, as each may possess different physiological adaptations and temperature tolerances. Despite a rich history of research on southern pine species, our basic understanding of temperature adaptation and genetic variation in temperature acclimation in pine species remains limited. Here, we conducted a common garden experiment with loblolly (Pinus taeda), longleaf (Pinus palustris), shortleaf (Pinus echinata) and slash pine (Pinus elliottii). Seedlings were sourced from at least three geographically distinct populations for each species, allowing us to assess genetic differentiation in temperature adaptation and acclimation between species and populations. Instantaneous temperature responses (15-40°C) of leaf-level respiration were measured at five timepoints throughout the season, capturing a 15°C range in average growth temperature during the thirty days prior to measurement. Using this approach, we tested the hypothesis that species and populations from cooler and more seasonal climates would show higher basal rates of leaf respiration and a greater capacity for seasonal temperature acclimation in comparison to species and populations from warmer and less seasonal climates. On average, longleaf pine showed the lowest rate of leaf respiration at a standard measurement temperature compared to all other species. However, longleaf pine showed no evidence of temperature acclimation or genetic differentiation in temperature acclimation at the population level. Within shortleaf pine and slash pine, populations differed in temperature acclimation of leaf respiration. Finally, loblolly pine showed the strongest evidence for temperature acclimation of leaf respiration, with all populations acclimating similarly. Although we found sound evidence of species differences in leaf respiration and some evidence of genetic differentiation in temperature acclimation, our results indicate that the home climate of southern pine species and populations may not be a strong predictor of physiological responses to temperature. Analysis of seedling growth and photosynthetic responses to temperature could provide further insight into species and population variation in carbon uptake, storage, and use. This work provides new information about the respiratory physiology of southern pine species and populations, and the ecological implications of these findings can inform forest climate adaptation strategies across the United States southeast.