Evaluation of Potential Herbivore Mediation of Plant Water Status in a North American Mixed-Grass Prairie

Abstract

Xylem water potentials (ip) were monitored diurnally from June through August 1981 to ascertain the water status of plants of four species growing on a heavily grazed prairie dog (Cynomys ludovicianus) colony and an adjacent lightly grazed uncolonized site in southwestern South Dakota. Highest p values were observed in June and August after periods of relatively high precipitation. Lowest values occurred in July when soil moisture had been depleted. However, there were no large differences in V of grasses (Agropyron smithii, Andropogon gerardi, and A. scoparius) growing on and off the prairie dog colony, even though root biomass of plants on the colony was substantially lower. While midday leaf conductance was comparable for A. smithii tillers on and off the colony, conductance values for A. gerardi and A. scoparius tillers were generally higher (17 to 60%) on the heavily grazed site. Artemisia frigida plants had slightly higher Vp on the prairie dog town during periods of moderate or high water stress. Soil moisture content was slightly but significantly (P _ 0.05) higher on the heavily grazed prairie dog town, even though afternoon soil temperatures at the 15-cm depth averaged 2.7°C higher.