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CONVERGING PATTERNS OF UPTAKE AND HYDRAULIC REDISTRIBUTION OF SOIL WATER IN CONTRASTING WOODY VEGETATION TYPES
Citation:
Meinzer, F. C., J R. Brooks, S. Bucci, G. Goldstein, F. G. Scholz, AND J. M. Warren. CONVERGING PATTERNS OF UPTAKE AND HYDRAULIC REDISTRIBUTION OF SOIL WATER IN CONTRASTING WOODY VEGETATION TYPES. TREE PHYSIOLOGY. Heron Publishing, Victoria, B.C, Canada, 24(8):919-928, (2004).
Description:
We used concurrent measurements of soil water content and soil water potential (Ysoil) to assess the effects of Ysoil on uptake and hydraulic redistribution (HR) of soil water by roots during seasonal drought cycles in six sites characterized by different types and amounts of woody vegetation and climatic regimes. The six sites included a semi-arid old-growth ponderosa pine (Pinus ponderosa Dougl. Ex Laws) forest, a moist old-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forest, a 24-yr-old Douglas-fir forest, and three Brazilian savanna sites differing with respect to tree density. In all of the sites, HR was confined largely to the upper 60 cm of soil. There was a common threshold relationship between the relative magnitude of HR and Ysoil among the six study sites. Below a threshold Ysoil of ~ ?0.4 MPa, overnight recharge of soil water storage increased sharply, and appeared to reach a maximum value of 80-90% recharge over a range of Ysoil from ~ ?1.2 to ?1.5 MPa. Although amounts of water hydraulically redistributed to the upper 60 cm of soil were relatively small (0 to 0.2 mm d-1), they greatly reduced the rates of seasonal decline in Ysoil. The effectiveness of HR in delaying soil drying diminished with increasing amounts of sapwood area per ground area. The relationship between soil water utilization and Ysoil in the 20 to 60 cm layer was nearly identical for all six sites. Soil water utilization varied with a surrogate measure of rhizosphere conductance in a similar manner at all six sites. The similarities in relationships between Ysoil and HR, soil water utilization, and relative rhizosphere conductance among the six sites suggested that despite probable differences in maximum rooting depth and density among them, there was a certain degree of convergence in biophysical controls on soil water utilization and redistribution in the upper soil layers where the density of finer roots is greatest.