HR: 1330h
AN: H33B-08    [Abstracts]
TI: Relative Contribution of Nighttime Transpiration to Daily Total Water Use by Tamarix in a Desert Riparian Woodland
AU: * Moore, G W
EM: gwmoore@tamu.edu
AF: Texas A&M University, 2126 TAMU, College Station, TX 77843-2126 United States
AU: Owens, K
EM: m-owens@tamu.edu
AF: Texas Agricultural Experiment Station, 1619 Garner Field Rd., Uvalde, TX 78801 United States
AB: The phreatophytic plant, Tamarix, consumes water from the Pecos River in west Texas, forming a narrow band of dense riparian woodland in an otherwise sparsely vegetated desert environment. Narrow desert riparian zones are largely influenced by dry desert air, creating favorable conditions for nighttime transpiration. In this study, we explore whether nighttime transpiration, especially on nights with warm temperatures and low relative humidity, significantly contributes to daily total water use by Tamarix. Sixteen stems were equipped with thermal dissipation sapflow sensors and monitored during the 2004 growing season. Relative humidity near the canopy did not exceed 70% on 18 of 213 nights and remained below 90% on 77 of 213 nights observed. Sapflow continued throughout most nights, reaching a minimum just before sunrise, as stem water capacitance refilled from the previous day's losses. Antecedent conditions strongly affected the transpirational response to high nighttime evaporative demands mostly likely because of stem water capacitance dynamics during and between rain events. Significant contributions of nighttime transpiration to daily total water use may partially explain how Tamarix is capable of using large amounts of water while maintaining moderate stem conductances. Diel patterns in Pecos River stream flow correspond with evapotranspiration losses from the Tamarix riparian woodland; however, quantitative interpretation must be based on an understanding of both daily and nightly transpiration.
DE: 1818 Evapotranspiration
DE: 1878 Water/energy interactions
SC: Hydrology [H]
MN: 2005 Joint Assembly