LB 32-265 - Investigating the drought physiology of northeastern trees: a turgor loss point perspective

As climate change has advanced, the Northeastern US has been subject to increasing drought conditions which are projected to become more extreme each year. By understanding tree response to drought we can better steward our ecosystems and foster resilient forest communities. We can gain insight into the drought tolerance of trees by quantifying the turgor loss point (TLP); the point generally at which leaves will wilt, close stomata, and/or have reduced photosynthesis. The specific questions we explored are: (1) How does the turgor loss point of northeastern tree species vary inter- and intra-specifically? And (2) How does this scale to whole-tree drought response?Leaf samples from thirteen species of trees were collected at the Bartlett Experimental Forest and Thompson Farm in New Hampshire in the summer of 2022. We processed the samples at Smith College using a vapor pressure osmometer to record the solute potential at full turgor and then converted it to turgor loss point. We then compared intraspecies data across elevational gradients at Bartlett Experimental Forest for Acer rubrum, Betula alleghaniensis, and Fagus grandifolia to determine the role of elevational microclimates in drought response. We also compared interspecies data across eleven different tree species at Thompson Farm.We found no large intra-specific differences across the elevational transect, however we did find large inter-specific differences. To understand both the drivers of this variation and how this variation scales to whole-tree response, we also compared the TLP from the elevational transects to sample height and the TLP data from Thompson Farm to whole-tree drought responses from the literature. This project allows us to further our understanding of how the northeastern US forest will respond to the changing climate.