PARENT SESSION
Contributed Oral Session 124: Grassland Ecology: Water Relations; Growth
Thursday, August 11, 8:00 AM - 11:30 AM, Meeting Room 518 C, Level 5, Palais des congrès de Montréal
Depth of water acquisition by invading sagebrush and resident herbs in a Sierra Nevada meadow.
Darrouzet-Nardi, Anthony*,1, D'Antonio, Carla2, Dawson, Todd3, 1 University of Colorado at Boulder, Boulder, CO, USA2 United States Department of Agriculture, Reno, NV, USA3 University of California, Berkeley, Berkeley, CA, USA
ABSTRACT- Woody shrub encroachment is a global trend in many semiarid ecosystems. Two-layer models of vertical soil water partitioning predict that declines in shallow soil moisture will favor woody plants. Due to stream channel incision, the semiarid meadows of the southern Sierra Nevada are experiencing long-term declines in soil moisture, and Rothrock sagebrush is invading the herbaceous meadows. We used stable oxygen isotope ratios in plant and soil water to measure the depth of plant water acquisition and thus test the appropriateness of a two-layer model during the early stages of sagebrush invasion. We found that a two-layer model does not apply well to this system, and that competition between sagebrush and resident herbs cannot be ruled out. Sagebrush used deeper water on average than most herbs, but it also acquired at least 10-30% of its water from shallow (<30 cm) soil. Likewise, many herbs acquired deep water, resulting in overlap in water use. This suggests that coexistence of shrubs and herbs during sagebrush invasion results not from vertical soil water partitioning, but from the survival of herbs that can cope with declining soil moisture, along with the replacement of shallow-water-dependent herbs by sagebrush.
Key words: Artemisia rothrockii, oxygen stable isotopes, semiarid riparian meadows, shrub encroachment