PARENT SESSION
Poster Session #32: Plant Ecology I.
Wednesday, August 8, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall
138
Belowground responses of Artemisia tridentata and Agropyron desertorum to summer rainfall events of two intensities in the Great Basin.
Yoder, Carolyn1, Menon, Usha1, Stark, John1, Caldwell, Martyn1, 1
ABSTRACT- A field study was conducted to evaluate belowground responses of Artemisia tridentata and Agropyron desertorum, common Great Basin shrub and grass species, respectively, to simulated 5-mm and 15-mm summer rainfall events. The simulated rainfall was labeled with K15NO3 (99 atom %) so that timing of plant nitrogen uptake could be monitored. In addition, soil NH4 and NO3 concentrations and physiological uptake capacities for NO3 and NH4 were determined before and after the rainfall events. Root growth in the top 15 cm of soil was monitored using a minirhizotron system. The nitrogen label was detected in aboveground tissue of Agropyron within 12 hours of both the 5-mm and 15-mm rainfall events. However, no nitrogen label was detected in aboveground tissue of Artemisia in the first 24 hours after labeling for either rainfall event. For Agropyron desertorum, root uptake capacity of NO3 increased significantly and equally for both the 5-mm and 15-mm rainfall events, although the increase persisted longer for the 15-mm event. In contrast, root physiological uptake capacities for NH4 increased significantly in Agropyron only in response to the 15-mm rainfall event. For the shrub, Artemisia tridentata, an opposite pattern of physiological root responses to that of Agropyron was observed in that there was a significant and equal increase in NH4 uptake capacity for the shrub in response to both the 5-mm and 15-mm rainfall events, but NO3 uptake capacity increased significantly only in response to the 15-mm event. Little or no root growth occurred for either species in response to either rainfall event. The results of this study indicate that both intensities of rainfall events can significantly increase the root nitrogen uptake capacity of both species. However, the timing of these responses and the predominate form of N uptake differed between species.
KEY WORDS: Agropyron desertorum, Artemisia tridentata, Great Basin, nitrogen uptake capacity