Water-use patterns among tallgrass prairie plant species: an isotopic approach.
Nippert, Jesse*,1, Knapp, Alan1, 1 Department of Biology, Fort Collins, CO, USA
ABSTRACT- Water availability governs grassland primary productivity, yet this resource varies in availability with time and space (soil depth). The ability of different species to use water from different depths in the soil profile remains unclear. However, documenting species differences in water-use may improve our ability to predict responses to water stress and drought tolerance at the community level. We report data from two growing seasons (2003-4) in which we measured the isotopic signature of plant xylem-water from eight species growing along topographic gradient within annually burned watersheds of the Konza Prairie Biological Station. Plant 18O was compared with soil water from increasing depths throughout the profile, as well as from recent rainfall events. Additionally, we measured seasonal changes in plant water potential in response to changes in soil volumetric water content. Species responses varied in time in both water-use and water-stress between dry (2003) and wet (2004) growing seasons. During dry periods, some woody and forb species have more depleted isotopic signatures compared to the dominant grasses, indicative of water-use from deeper portions of the soil profile. However, during wet periods in the growing season, minimal species differences in water use were evident, suggesting common dependence on recent rainfall events. Similarly, plants in uplands had enriched signatures compared to lowlands, but the greatest differences across topography occurred during dry periods. In both years, upland soils were drier than in other locations and exhibited a greater amount of variability. In general, plants with the ability to use water from multiple sources exhibited reduced variability in water potential; however, interspecific differences in plant water potentials were highest during dry periods. Documenting species-specific differences in water use will help refine predictions of grassland community responses to altered climatic patterns.
Key words: seasonal water availability, 18O, drought stress, tallgrass prairie
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