SPIKE II: Tree water status drives source water partitioning (PhD)
In collaboration with the ECHO Lab at the École Polytechnique Fédérale de Lausanne (EPFL), we used a 2 m3 lysimeter with willow trees (Salix viminalis) planted within, to conduct a high spatial-temporal resolution experiment - The SPIKE II. Here, we combine isotope data in xylem and soil water with measurements of tree’s physiological information including tree water deficit (TWD), fine root distribution, and soil matric potential, to investigate the mechanism driving tree water source partitioning. TWD provided an integrated response of plant water status to water supply and demand. The combined isotopic and TWD measurement showed that short-term variation (within days) in source water partitioning is determined mainly by plant hydraulic response to changes in soil matric potential. We observed changes in the relationship between soil matric potential and TWD that are matched by shifts in source water partitioning. Our results show that tree water use is a dynamic process on the time scale of days. These findings demonstrate tree’s plasticity to water supply over days can be identified with high-resolution measurements of tree water status. More info: Nehemy et al .
BERMS: Tree water use in the cold Critical Zone (PhD)
I am investigating plant water use at two long-term study sites within the Boreal Ecosystem Research and Monitoring Sites (BERMS) in Saskatchewan, Canada. This work uses vapor water fluxes (eddy covariance), soil water conditions, tree sap flow velocities, and the longest band-dendrometer dataset in the boreal forest in Canada. Besides these hydrometric measurements, we collected weekly-resolution stable isotopes measurements of xylem water of three different tree species (Picea mariana, Larix laricina and Pinus banksiana), soil, precipitation, groundwater and stream. The project leverages these high-temporal resolution monitoring of water fluxes along well defined phenological phases to understand the effect of phenology (e.g. stem rehydration) and tree water status on patterns of tree water use and its impact on hydrological processes in northern ecosystems.
Preliminary results from our investigation can be found below: