Document: DAN-3-34-61

The responses of fine roots on patches of water and nitrogen in two dominant Mojave Desert shrubs.

OBRIST, D.* and J.A.ARNONE

Desert Research Institute, Reno, NV 89512 USA ¹

Abstract:
The ability of fine roots to proliferate into favorable patches of water and water-plus-nitrogen was studied in two dominant shrub species in the Mojave Desert - Larrea tridentata (Creosote bush) and Ephedra nevadensis (Mormon tea bush). This potential root response could represent the ability of plants to take advantage of additional availability of water and nitrogen caused by increased spring and early-summer precipitation expected under global warming and by additional nitrogen deposition by metropolitan areas in southern Nevada and California. In a field study, we tested the following hypotheses: 1) adult shrubs of Larrea and Ephedra respond to patches of additional water and water-plus-nitrogen by increased fine root proliferation into the patches; 2) patches with water-plus-nitrogen result in a stronger fine root response than patches of water alone since the Mojave Desert is both water and nitrogen limited; and 3.) fine root proliferation into patches depends on season and will be more pronounced after rainfall events, or in pre-watered plots, when plants are in a more active physiological state. We reject all three hypothesis since no detectable increase in fine root density was detected in patches of water and water-plus-nitrogen compared to unwatered and unfertilized control patches. Surprisingly, higher water availability in pre-watered plots lead to decreased root densities in Larrea instead of an expected root growth due to favorable conditions, whereas Ephedradid not show significant changes. Thus, our current data showing a lack of fine root proliferation into patches of water and water-plus-nitrogen suggest that capturing short-term localized resource patches may not be an important strategy for these plants - at least not in upper soil horizons (0-30 cm) in dry years.

Keywords: Larrea tridentata, Ephedra nevadensis, fine root, water, nitrogen

This abstract is being presented at: 3:45 PM in session:
Oral Session #12: Roots.