How does plant hydraulicsgovern the soil-vegetation-atmosphere transport of water?

Recent initiatives to improve global land surface models have focused on including understanding about plant hydraulics to better represent stress-induced reductions in transpiration during drought. It is assumed that plant hydraulic processes may also have a profound impact on the catchment water balance during water stress. A common factor that is known to inhibit the water transport in plants is cavitation. The latter occurs in two instances. The first being air entry through the pit valves on the walls of the xylem. The second is that at the very low pressures of transport, water can change from a liquid to a gaseous state, breaking the continuous flow of liquid. Various physical characteristics of the xylem influence the efficiency of transport and the vulnerability to cavitation. Here we present some experiments designed to illustrate the principles of plant water transport and its failure using plant parts and plant replica under well-controlled but close to natural conditions. Preliminary results are quite surprising and display phenomena that are not easily reconciled with standard understanding of water flow through plants. Further targeted experiments to shed more light onto the subject and its implications for hydrological processes will be discussed.Funded by the Luxembourg National Research Fund, ATTRACT programme (A16/SR/11254288