Response of Artemisia tridentata ssp. wyomingensis and Stipa thurberiana to Nitrogen Amendments

Abstract

-Artemisia tridentata has increased dramatically during the past 100 yr throughout the sagebrush steppe at the expense of late-seral perennial grasses. This study was designed to determine the effects of addition or depletion of different nitrogen forms on aboveground vegetative and reproductive growth of Artemisia tridentata ssp. wyomingensis and Stipa thurberiana, a late-seral grass. Treatments included application of sugar (45 g m-2), nitrate (4.5 g N m-2), ammonium (4.5 g N m-2) and a control. Both nitrogen forms significantly increased Stipa aboveground biomass and tiller density. Individual tiller weight was not different among treatments. Added nitrogen also increased aboveground biomass, total shoot density and individual shoot weight in Artemisia. Biomass production, however, was greater in the nitrate plots than the ammonium plots. Reproductive shoot weight and density for Artemisia, and density for Stipa were greater in nitrate than the ammonium, sugar and control plots. Reproductive shoot density increased 350% and 294% over controls for Stipa and Artemisia, respectively. Aboveground biomass increased by a significantly greater percentage in Artemisia than Stipa in nitrogen treated plots. Based on aboveground response, data suggests that Artemisia responds more to available nitrogen than Stipa.