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United States Department of Agriculture

Agricultural Research Service

Research Project: HYDROLOGIC PROCESSES, SCALE, CLIMATE VARIABILITY, AND WATER RESOURCES FOR SEMIARID WATERSHED MANAGEMENT

Location: Southwest Watershed Research

Title: Shrub encroachment alters sensitivity of soil respiration to temperature and moisture 2115

Authors
item Cable, J.M. -
item Barron-Gafford, G.A. -
item Ogle, K. -
item Pavao-Zuckerman, M. -
item Scott, Russell
item Williams, D.G. -
item Huxman, T.E. -

Submitted to: Journal of Geophysical Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 3, 2011
Publication Date: January 11, 2012
Repository URL: http://10.1029/2011JG001757
Citation: Cable, J., Barron-Gafford, G., Ogle, K., Pavao-Zuckerman, M., Scott, R.L., Williams, D., Huxman, T. 2012. Shrub encroachment alters sensitivity of soil respiration to temperature and moisture. Journal of Geophysical Research. 117:1-11.

Interpretive Summary: Shrub encroachment into grasslands has been occurring over the past century around the world. Shrub encroachment creates patchier landscapes, but it is unclear how this change affects soil processes like soil carbon dioxide respiration. We quantified the response of soil respiration to different understory conditions created by large mesquite shrubs, medium-sized mesquite, sacaton bunchgrasses, and open spaces in a semiarid riparian shrubland. Field and incubation respiration data were analyzed in a complex statistical framework, which revealed that the magnitude of respiration is higher under large shrubs, but medium shrubs have a lower magnitude than grasses. The temperature sensitivity of respiration is higher near the trunk of large shrubs compared to the other locations, but this differed from the moisture sensitivity. This study highlights the need to more completely understand changes in the spatial patterns in soil processes as a function of shrub encroachment within riparian areas, and the manner in which these processes combine to influence landscape carbon balance.

Technical Abstract: Shrub encroachment into grasslands creates a mosaic of different soil microsites ranging from open spaces to well-developed shrub canopies, and it is unclear how this affects the spatial variability in soil respiration characteristics, such as the sensitivity to soil temperature and moisture. This is particularly important in semiarid riparian systems where the scaling of ecosystem carbon fluxes with increased shrub cover is non-linear due to groundwater access by large shrubs. We quantified the response of soil respiration to different microsite conditions created by large mesquite shrubs (near the trunk and the canopy edge), medium-sized mesquite, sacaton bunchgrasses, and open spaces in a semiarid riparian shrubland. We hypothesized that soil respiration would be more temperature sensitive, less moisture sensitive, and have a higher magnitude in shrub microsites (particularly big relative to medium sized shrubs) compared to grass and open microsites. Field and incubation respiration data were analyzed in a Bayesian framework to quantify the microsite-specific temperature and moisture sensitivities and magnitude of respiration. This revealed that the magnitude is higher under large shrubs, but medium shrubs have a lower magnitude than grasses. The temperature sensitivity of respiration is higher near the trunk of large shrubs compared to the other microsites, but this differed from the moisture sensitivity. This study highlights the need to more completely understand changes in the spatial patterns in soil processes as a function of shrub encroachment within riparian areas, and the manner in which these processes combine with greater carbon gain potential to influence landscape carbon balance.

Last Modified: 4/20/2014
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