Continuous stem water potential measurements of a diffuse-porous tree
species offer new insights into tree water relations
Abstract
Water potential is a crucial parameter for assessing tree water status
and hydraulic strategies. However, methods for measuring water
potential, such as the Scholander pressure chamber, are destructive and
discontinuous, and difficult to perform in tall forests. Consequently,
important dynamics in water potentials, particularly during short-term
drought, are difficult to capture. Recent advancements have introduced
low-maintenance sensors capable of measuring continuous, high-resolution
stem water potentials. If applicable to forest trees, such sensors hold
the potential to significantly enhance our understanding of tree water
relations. We evaluated these sensors in a temperate, diffuse-porous
tree species ( Carpinus betulus) over a growing season marked by
dry-down periods and heat. Concurrent measurements of branch water
potential, sap flow, and environmental factors (air temperature, vapor
pressure deficit, and soil water content) were conducted. Midday stem
water potentials of C. betulus reached minimum values of -3.39 ±
0.10 MPa and exhibited pronounced seasonal fluctuations, mirroring
changes in environmental conditions and sap flow. Comparison of stem
water potentials with Scholander-type measurements revealed a very good
correlation with predawn (R 2 = 0.98) and a general
agreement with midday measurements (R 2 = 0.71).
Diurnal variations in stem water potentials and sap flow exhibited a
hysteresis, consistent with other plant parameters. In this first
assessment, the agreement with Scholander-type measurements, sap flow,
and environmental parameters suggests the tested water potential sensors
yield reliable data. If applicable to other tree species, including
conifers, these sensors could significantly advance our understanding of
tree water relations and their role in forest drought responses.