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Title: Seasonally contrasting responses of evapotranspiration to warming and elevated CO2 in a semiarid grassland

Author
item SOROKIN, Y - University Of Wyoming
item ZELIKOVA, T - University Of Wyoming
item Blumenthal, Dana
item WILLIAMS, D - University Of Wyoming
item PENDALL, E - University Of Sydney

Submitted to: Ecohydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: In dry grasslands, global climate change is expected to alter water loss from both plants and soils (evapotranspiration, or ET). While climate change will involve elevated CO2 and increased temperatures, independently these factors may have different impacts on ET due to their opposing effects on transpiration. We quantified ET in a semi-arid grassland altered by elevated CO2 and warming over three years with contrasting ambient precipitation. Seasonal and interannual variations in ET were larger than the effects of climate manipulation treatments. On dates when treatments impacted ET, warming increased ET early in the growing season and suppressed ET later in the growing season. Elevated CO2 suppressed ET early in the growing season. Vegetation greenness (a proxy for leaf area) and soil moisture were the strongest predictors of ET. Our research demonstrates that effects of increased atmospheric CO2 and temperature on ET will be mediated by the timing of plant development and climatic conditions.

Technical Abstract: Global climate change is expected to alter seasonal patterns and rates of evapotranspiration (ET) in dry regions. While climate change will involve elevated CO2 and increased temperatures, independently these factors may have different impacts on ET due to their opposing effects on transpiration. We used canopy gas exchange chambers to quantify ET in a semi-arid grassland altered by elevated CO2 and warming over three years with contrasting ambient precipitation. Seasonal and interannual variations in ET were larger than the effects of climate manipulation treatments. On dates when treatments impacted ET, warming increased ET early in the growing season and suppressed ET later in the growing season. Elevated CO2 suppressed ET early in the growing season. Vegetation greenness (a proxy for photosynthetically active leaf area) and soil moisture were the strongest predictors of ET. Our research demonstrates that effects of increased atmospheric CO2 and temperature on ET will be mediated by plant phenological development and antecedent climatic conditions.