Impact of soil hydraulic properties on water-soil-plant relations

Modeling stomatal response to soil drying is of crucial importance for estimating transpiration fluxes. There is a critical need for a better quantification of the impact of soil water limitation on vegetation in order to predict more accurately the impact of climate change on natural ecosystems and adapt agricultural practices.

Recently, we proposed a simple conceptual model, which predicts how soil and plant hydraulics affect transpiration.  This model reconciles soil- and root-based perspectives on drought stress and defines a 3D surface, which represents the maximum possible transpiration rate that can be sustained by a soil-plant system. The shape of this surface shows two distinct zones: a linear zone where the increase of transpiration is proportional to the difference of potential between soil and root and a non linear part in which an increase of E generates a huge decrease of leaf water potential. We show that this nonlinearity is mainly controlled by below ground hydraulic conductance. We hypothesize that plants should avoid this non linear zone by (1) adapting their short term stomatal regulation and (2) ensuring long term coordination between canopy and root hydraulics with growth. It implies that difference in soil hydraulics will lead to contrasted plant hydraulic and structural vegetation properties. Evidences exist at plant scales that this coordination exists. We further discuss how this might affect (agro-)ecosystem-water relations.