Ring- and diffuse-porous species exhibit a spectrum of hydraulic behaviors from isohydry to anisohydry in a temperate deciduous forest

Key message: Diffuse-porous Acer saccharum and ring-porous Carya ovata exhibit opposing isohydry and anisohydry, respectively, but physiological responses of four other species indicate a spectrum of hydraulic behaviors among co-existing mature temperate trees. Abstract: Temperate forests maintain a high species abundance, yet we do not fully understand how co-existing temperate tree species differentially respond to water stress. The iso/anisohydric spectrum provides a framework for contextualizing and comparing hydraulic behavior. Using this framework, we wanted to understand how hydraulic behavior differs between several mature canopy-dominant tree species in a temperate deciduous forest. We assessed multiple hydraulic parameters across the 2019 growing season in three diffuse-porous species (Acer saccharum, Fagus grandifolia, and Platanus occidentalis) and three ring-porous species (Quercus alba, Quercus rubra, and Carya ovata). We measured sap flux and leaf water potential, along with soil moisture and vapor pressure deficit over the growing season. We also collected pre-dawn leaf water potential measurements in July in addition to the mid-day measurements. Our data reveal a range of hydraulic behaviors from isohydric Acer saccharum at one end of the continuum, to anisohydric Carya ovata at the other end, with the other four species exhibiting intermediate hydraulic behaviors between these two “extremes”. The range of hydraulic behaviors exhibited among co-existing temperate tree species suggests multiple strategies for coping with water stress within a single forest. Defining species-specific strategies will be important for predicting how the structure and composition of temperate forests may respond to changes in climate, particularly water availability.