This project investigates the effect of land-atmosphere (L-A) coupling on vegetation water use and photosynthesis. It integrates controlled laboratory and field experiments with continuous monitoring of within-canopy micro-meteorological conditions and plant drought stress, with the specific sub-objective to represent the role of land-atmosphere coupling in an optimality-based vegetation model. The project will improve our understanding of stomatal control on transpiration and phosynthesis, extending observations of L-A feedback down to the canopy air space, and investigating the effect of extreme heat and/or drought on stomatal control and hence transpiration, with its ramifications for sensible heat flux and potential long-term effects due to heat damage to foliage. A specific focus will be put on 1) the effects of vertical mixing of air on leaf and canopy water use efficiency, 2) the effects of vertical mixing of air on leaf temperatures and thus on plant heat stress (especially during dry periods), 3) the potential to improve the simulation of transpiration, soil water dynamics and CO2 assimilation by optimality-based vegetation dynamics and stomatal control compared to conventional parameterizations of vegetation and stomatal dynamics.
