Detailed in-situ leaf energy budget permits the assessment of leaf
aerodynamic resistance as a key to enhance non-evaporative cooling under
drought
Abstract
The modulation of the leaf energy budget components to maintain optimal
leaf temperature are fundamental aspects of plant functioning and
survival. Better understanding these aspects becomes increasingly
important under a drying and warming climate when cooling through
evapotranspiration (ET) is suppressed. Combining novel measurements and
theoretical estimates, we obtained unusually comprehensive twig-scale
leaf energy budgets under extreme field conditions in droughted
(suppressed ET) and non-droughted (enhanced ET) plots of a semi-arid
pine forest. Under the same high mid-summer radiative load, leaf cooling
shifted from relying on nearly equal contributions of sensible (
H) and latent ( LE) energy fluxes in non-droughted trees
to relying almost exclusively on H in droughted ones, with no
change in leaf temperature. Relying on our detailed leaf energy budget,
we could demonstrate that this is due to a 2× reduction in leaf
aerodynamic resistance. This capability for LE-to-H shift in leaves of
mature Aleppo pine trees under droughted field conditions without
increasing leaf temperature is likely a critical factor in the
resilience and relatively high productivity of this important
Mediterranean tree species under drying conditions.