PNNL

Abstract

The plasticity of root water uptake determines the maintenance of transpiration during periods of water limitation and drought. However, representation of soil-to-root water transfer for individual root systems and the implications of water uptake strategies at the ecosystem scale remain elusive. We model three-dimensional root water uptake under variably saturated conditions for a one-hectare temperate forest plot for a growing season with a pronounced mid-season dry period. Variations in root architecture, hydraulic properties, and degree of lateral interaction between root systems produce divergent local responses to water limitation and provide insights on individual and community response to meteorological conditions. Results demonstrate plasticity of ecosystem-scale responses to surface drying, where interacting roots shift regions of active uptake to deeper soil layers with less abundant root biomass. Our model results further demonstrate that root lateral interactions are beneficial at the ecosystem-scale, even under conditions of individual competition for water. Specifically, a more spatially extensive root system facilitates access to a larger soil water reservoir, often ameliorating water limitation, benefits that can be offset by construction and maintenance costs. A plausible “viability” region of tree communal co-existence is therefore implied where competitive pressures and carbon allocation costs are balanced by a perceived water benefit.