Root-zone “Periscope” and its applications for investigating plant-soil water relations and transpiration modelling

Since the first stoma appeared about 400 million years ago, moisture exchange between lands and the atmosphere extends into the root zone. However, due to its invisibility from the surface, root distribution and its temporal variation are difficult to estimate, which greatly hinders investigation of root zone moisture dynamics, soil-plant water relations, and transpiration modelling. Plant water potential reflects dynamic water condition in vegetation, which is determined by moisture supply in the root zone, atmospheric demand, and plant physiological control. Thus, dynamic water potential can provide a “periscope” to observe root zone hydraulic conditions. Based on this hydraulic connection in the soil-plant-atmosphere continuum (SPAC), plant individuals work very likely as “observation wells” to the whole root zone at predawn, and as “pumping test wells” in daytime. Meanwhile, stable isotopic composition of water in plant xylem approximately reflects the isotopic signature of bulk root accessible moisture. These hydraulic and isotopic root-zone periscopes provide information to estimate root-zone and plant hydraulic states and their dynamics, and hydraulic properties. In this presentation, we will show how this root-zone periscope concept, based on continuous monitoring of plant water potential, sapflow, and/or isotopic composition of xylem water, has been successfully applied in SPAC model development, root water uptake model improvement, transpiration model parameterisation, as well as investigation of ecohydrological separation.