Water potential, water content, and net assimilation of some boreal forest mosses

Abstract

Relationships between water content and water potential for Hylocomium splendens (Hedw.) B.S.G., Pleurozium schreberi (Brid.) Mitt., Ptilium crista-castrensis (Hedw.) De Not., and Tomenthypnnm nitens (Hedw.) Loeske, the last occurring in a distinctly different habitat from the first three, showed no hysteresis effect between wetting and drying curves and no appreciable differences among the species.Water contents near equilibrium over distilled water (water potential near zero) were 10–20% of saturation water contents, which suggested that after saturation by rainfall, considerable water loss can take place before water stress is experienced.The capacity for net assimilation decreased with depth in the moss canopy in all species, and the species showed similar decreases in net assimilation rates with decreasing water contents, from maximum rates at 3 to 6 g H2O g−1 dry weight to near or below zero rates around 0.4 g H2O g−1 dry weight.