Vulnerability to cavitation and response of canopy conductance to root cavitation in five southeastern US pine species

Abstract

Although the Southeastern United States generally receives considerable precipitation and total precipitation has slightly increased, the region has experienced recent recurrent droughts and is anticipated to encounter more severe droughts as a result of increasing temperature. Knowledge of plant water transport and plant organ hydraulics facilitates our understanding of the capabilities of forests to withstand drought under a changing climate. In this project, we studied five pine species that are ecologically or economically important in the Southeastern US, namely Pinus virginiana (Virginia pine), P. echinata (shortleaf pine), P. taeda (loblolly pine), P. elliottii (slash pine), and P. palustris (longleaf pine). The overarching goal is to understand and compare their hydraulic performance under droughts, and we addressed the goal from two perspectives. First, we compared hydraulic properties associated with vulnerability to embolism curves for terminal branches and lateral roots in the topsoil. Second, we investigated the stomatal regulation strategies adopted by these species. For this purpose, we studied the response of canopy conductance index (GcI) to the estimated in situ loss of conductivity in roots (PLCroot) during the growing season of 2019. Two methods of estimating soil water potential, from which PLCroot was computed, were used by either assuming random noise in measurements on soil texture or assuming representation of microsite variability by the measurements. Overall, the results suggest that the two short-needle species, P. virginiana and P. echinata, are likely to be more resistant to drought by the combined benefit of higher resistance to cavitation in roots and moderate to conservative regulation of GcI. The study also calls attention to the assumption made for microsite variability in soil texture, when using common garden to study relationships among functions of different organs that entail soil water conditions.