Soil and xylem water potential and soil water content in contrasting Pinus contorta ecosystems,Southeastern Wyoming,USA

Summary The relationships between volumetric soil water content (), in situ soil water potential (_soil) and predawn xylem pressure potential (_predawn) were quantified in four contrasting lodgepole pine ecosystems in Wyoming, USA. On three of the sites, changes in _soil correlated closely with _predawn, but on a porous soil derived from coarse granitic parent material, _predawn declines occurred much sooner than corresponding declines in _soil, possibly because of local depletion of rhizosphere moisture and low molecular diffusivity of water in that soil. Exptrapolation of laboratory-derived characteristic curves for soil moisture to field conditions yielded different relationships between and _soil than curves derived from in situ measurements, probably because of disruption of soil structure and porosity during sample collection and handling in laboratory studies. Although a close correlation between and _predawn was observed, future efforts at modelling the soil-plant-atmosphere continuum should be directed towards a more detailed understanding of the complex relationships between _soil at varying depths and plant water stress.