A. J. Leffler

RAPID SOIL MOISTURE RECHARGE TO DEPTH BY ROOTS IN A STAND OF ARTEMISIA TRIDENTATA

The temporal patterns of soil water potential in a stand of Artemisia tridentata in central Utah, USA, were monitored during the summer, which included small periodic rainfall events, and over the winter, when most of the soil recharge occurs in this environment. The pattern of recharge, when compared to an area cleared of aboveground vegetation, strongly indicated that the downward movement of water to 1.5 m was primarily conducted via roots by the process known as hydraulic redistribution. Rainwater was moved rapidly downward shortly after the rain event and continued over a period of a few days. For rainwater reaching a 0.3–1.5 m depth, the portion redistributed by roots was estimated to range from 100% for small rainfall events (<8 mm) to 74% for a 36-mm event. Simulations with a model of soil water movement that compared situations with and without hydraulic redistribution by roots, indicated that during the fall–spring recharge period, 67% of all water moved downward below 0.1 m was via roots, while...

Water conservation in Artemisia tridentata through redistribution of precipitation

Water conservation is important for plants that maintain physiologically active foliage during prolonged periods of drought. A variety of mechanisms for water conservation exist including stomatal regulation, foliage loss, above- and below-ground allocation patterns, size of xylem vessels and leaf pubescence. Using the results of a field and simulation study with Artemisia tridentata in the Great Basin, USA, we propose an additional mechanism of water conservation that can be used by plants in arid and semi-arid environments following pulses of water availability. Precipitation redistributed more uniformly in the soil column by roots (hydraulic redistribution of water downward) slows the rate at which this water can subsequently be taken up by plants, thus prolonging water availability during periods of drought. By spreading out water more uniformly in the soil column at lower water potentials following precipitation events, water use is reduced due to lower soil conductivity. The greater remaining soil water and more uniform distribution result in higher plant predawn water potentials and transpiration rates later in the drought period. Simulation results indicate that plants can benefit during drought periods from water storage following both summer rain events (small summer pulses) and overwinter recharge (large spring pulse). This mechanism of water conservation may aid in sustaining active foliage, maintaining root-soil hydraulic connectivity, and increasing survival probability of plants which remain physiologically active during periods of drought.