The sensitivity of ecosystem carbon exchange to seasonal precipitation and woody plant encroachment |
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Authors: | D L Potts T E Huxman R L Scott D G Williams D C Goodrich |
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Institution: | (1) Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA;(2) Ecology and Evolutionary Biology, University of California, 321 Steinhaus Hall, Irvine, CA 92697, USA;(3) Southwest Watershed Research Center, USDA-ARS, Tucson, AZ 85719, USA;(4) Renewable Resources and Botany, University of Wyoming, Laramie, WY 82071, USA |
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Abstract: | Ongoing, widespread increases in woody plant abundance in historical grasslands and savannas (woody encroachment) likely will interact with future precipitation variability to influence seasonal patterns of carbon cycling in water-limited regions. To characterize the effects of woody encroachment on the sensitivity of ecosystem carbon exchange to seasonal rainfall in a semi-arid riparian setting we used flux-duration analysis to compare 2003-growing season NEE data from a riparian grassland and shrubland. Though less seasonally variable than the grassland, shrubland NEE was more responsive to monsoon rains than anticipated. During the 2004-growing season we measured leaf gas exchange and collected leaf tissue for δ13C and nitrogen content analysis periodically among three size classes of the dominant woody-plant, Prosopis velutina and the dominant understory species, Sporobolus wrightii, a C4 bunchgrass, present at the shrubland. We observed size-class and plant functional type independent patterns of seasonal plant performance consistent with greater-than-anticipated sensitivity of NEE in the shrubland. This research highlights the complex interaction between growing-season precipitation, plant-available alluvial groundwater and woody plant abundance governing ecosystem carbon balance in this semi-arid watershed. |
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Keywords: | Flux-duration analysis Photosynthesis Woody encroachment Precipitation variability |
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