HR: 17:35h
AN: B34A-06    [Abstracts]
TI: Patterns of soil water infiltration and extraction as a major determinant for vertical root distributions
AU: * Schenk, H
EM: jschenk@fullerton.edu
AF: California State University Fullerton, Department of Biological Science, PO Box 6850, Fullerton, CA 92834-6850, United States
AB: Plants and their roots are the most important source for organic carbon in the soil. Understanding vertical distributions of soil carbon inputs therefore requires knowing the factors that shape vertical root distributions. Where water availability is limiting plant growth, soil water infiltration patterns are likely to shape vertical root distributions. In arid climates with high temporal variability of precipitation, shallow water infiltration is most common and therefore the most reliable, but most short-lived plant water source and deep infiltration the most rare, most long-lived, but least reliable water source. In contrast, in seasonally dry, semi-arid to sub-humid climates, a seasonal water surplus can accumulate at depth and thus be available through deep roots during the dry season. Based on these differences, it is predicted that rooting depths in arid climates are limited by infiltration depths, while seasonally dry climates should favor deep roots, especially in climates with a pronounced wet-season surplus of water. These predictions were tested using data collected in two global databases. The RPGE database contains 564 vertical root profiles of global ecosystems, while the RSIP database contains shapes and sizes of root systems for 2349 individual plants. Data from both databases supported the prediction of infiltration depths as a major factor limiting rooting depths in dry environments as well as the prediction of very deep roots in seasonally dry climates with reliable wet seasons. The relationship between water infiltration patterns and vertical root distributions was formalized in a Soil Water Infiltration and Extraction Model (SWIEM), which models soil water infiltration through 500 discrete soil layers to a depth of 5 m. Water extraction proceeds from the top down, with extraction depths determined by potential evapotranspiration and the vertical distribution of soil water. The hypothesis that water extraction patterns would be predictive of vertical root distributions was tested for eight root profiles from different biomes. Predicted soil water extraction patterns matched observed vertical root distributions very well, thereby suggesting that water infiltration and extraction patterns are indeed a major determinant for vertical root distributions.
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0476 Plant ecology (1851)
DE: 1813 Eco-hydrology
DE: 1838 Infiltration
DE: 1866 Soil moisture
SC: Biogeosciences [B]
MN: 2007 Joint Assembly