Reinhardt, Keith , Germino, Matthew .
Desert shrub responses to seasonal timing of precipitation are contingent on soil depth: long-term experimental evidence, from leaves to populations.
Climate change ispredicted to alter the variability of precipitation and soil water storage in arid environments. We examined how 17years of experimental changes in precipitation seasonality affected cover, crown and canopy volume, population density, and ecophysiology of big sagebrush (Artemisia tridentata) relative to soil water content, in plots with shallow or deep soils. We hypothesized that supplemental winter precipitation (WIN) would favor shrub growth at organism and population scales via increased soil water storage, relative to ambient (AMB) and supplemental summer (SUM) precipitation. WIN increased volumetric soil water content 4-8 percentage points (i.e., 18% to 22%) relative to AMB, resulting in abundant and uniformly distributed soil water through July in most years. WIN resulted in greater shrub cover, crown and canopy size (volume), and density (individuals/m2) relative to both SUM and AMB in deep-soil plots, but WIN reduced shrub cover and size in plots with shallow soils (1 m depth). SUM increased water content of the top 40 cmof soil by 2-4 percentage points, but did not increase shrub size and cover. These treatment effects suggest a strong role for deep soil water, yet AIC modeling analysis showed that water in both the shallowest (0-20 cm) and deepest (>1 m) soil depths were important predictors of shrub growth. Instantaneous photosynthetic gas exchange and plant water potentials were similar among the treatments throughout the growing season, but more negative d13C of sagebrush shoots in WIN indicated decreased water-use efficiency throughout the growing season. Our experimental results suggest that the seasonal timing of precipitation has equal or greater effects compared to the amount of annual precipitation on this dominant and widespread shrub species. However, strong and predictable soil-depth contingencies on the effects of precipitation seasonality presage a landscape mosaic of changes in shrub abundance due to climate change.
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1 - Idaho State University, Biology, Pocatello, ID, 83209, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Forsyth Room/Chase Park Plaza
Date: Monday, July 11th, 2011
Time: 3:05 PM