Understanding and parameterizing the soil-water-atmosphere transfer through vegetation

We present an overview of water transport in plants, exploring how the theory has formed the basis of models of water use, carbon assimilation and plant growth. We outline the cohesion theory of water transport, and explore the vulnerabilities of the transport system to cavitation. The relationships between water relations and CO2 gain are outlined using a detailed model of the soil–plant–atmosphere continuum, coupling vapour-phase losses of water to liquid-phase supply to the leaf. Measurements of whole ecosystem exchange of latent energy and CO2 via eddy covariance are increasingly common. These measurements are generated almost continuously, and so provide time series of land-surface process dynamics that have proved very useful for testing models. We compare model predictions of canopy water and C exchange for temperate deciduous/broadleaf and evergreen/coniferous forest, tropical rain forest, and a range of arctic tundra vegetation types. From these comparisons, we summarize the critical issues for parameterizing water fluxes through vegetation. We then go on to discuss how land-surface schemes can be coupled to atmospheric mesoscale model