Progress in Botany

Volume 69 of the series Progress in Botany pp 397-422

Functional Differences in Soil Water Pools: a New Perspective on Plant Water Use in Water-Limited Ecosystems

  • Ronald J. RyelAffiliated withDepartment of Wildland Resources and the Ecology Center, Utah State University
  • , Carolyn Y. IvansAffiliated withCampbell Scientific, Inc.
  • , Michael S. PeekAffiliated withDepartment of Biology, William Paterson University
  • , A. Joshua LefflerAffiliated withDepartment of Wildland Resources and the Ecology Center, Utah State University

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Arid and semi-arid ecosystems cover roughly half of the earth's surface. Significant changes in vegetation cover combined with climate change have increased concern over the future of these lands, which have considerable economic importance. Much research has focused on plant—soil water relations in these systems, yet many mechanisms and significance of water use patterns are not well under-stood. Here we describe a new conceptual model that considers two pools of soil water accessed by plants: a growth pool that is located in shallow soil layers, and a maintenance pool that is often in deeper soil layers. While they may be spatially and temporally separated when used, these pools are largely separated by function and have different dynamics and competitive interactions. The growth pool is characterized by rapid use and high competition among plants, is exploited during the period of high resource acquisition and growth, and couples directly to nutrient availability. The maintenance pool is characterized by low competition, persistence, and is largely decoupled from nutrient resources. We argue that, by assessing the functional importance of soil water pools, we are able to more effectively assess how changes in hydrology related to climate, vegetation or land-use alterations may affect plant communities and ecosystem function. We also explore the mechanisms plants use to conserve water and discuss the significance of feedforward and feedback control.