Abstract
A greater abundance of shrubs in semiarid grasslands affects the spatial patterns of soil temperature, moisture, and litter, resulting in fertile islands with potentially enhanced soil metabolic activity. The goal of this study was to quantify the microsite specificity of soil respiration in a semiarid riparian ecosystem experiencing shrub encroachment. We quantified the response of soil respiration to different microsite conditions created by big mesquite shrubs (near the trunk and the canopy edge), medium‐sized mesquite, sacaton bunchgrasses, and open spaces. We hypothesized that soil respiration would be more temperature sensitive and less moisture sensitive and have a greater magnitude in shrub microsites compared with grass and open microsites. Field and incubation soil respiration data were simultaneously analyzed in a Bayesian framework to quantify the microsite‐specific temperature and moisture sensitivities and magnitude of respiration. The analysis showed that shrub expansion increases the heterogeneity of respiration. Respiration has greater temperature sensitivity near the shrub canopy edge, and respiration rates are higher overall under big mesquite compared with those of the other microsites. Respiration in the microsites beneath medium‐sized mesquites does not behave like a downscaled version of big mesquite microsites. The grass microsites show more similarity to big mesquite microsites than medium‐sized shrubs. This study shows there can be a great deal of fine‐scale spatial heterogeneity that accompanies shifts in vegetation structure. Such complexity presents a challenge in scaling soil respiration fluxes to the landscape for systems experiencing shrub encroachment, but quantifying this complexity is significantly important in determining overall ecosystem metabolic behavior.
Highlights
[3] Shrub expansion into grasslands significantly redistributes soil CO2 efflux activity on the landscape, creating respiration “hot spots” beneath shrub canopies [Hibbard et al, 2001; McCulley et al, 2004]
Toward improving the respiration models, we explored incorporating the effects of the Enhanced Vegetation Index (EVI) to account for changes in ecosystem vegetation “activity” on soil respiration
16 day Moderate Resolution Imaging Spectroradiometer (MODIS) EVI data were used as a proxy for ecosystem leaf area index during the growing season in 2005, as Scott et al [2006] found a linear relationship between the two measures
Summary
[2] In arid and semiarid ecosystems worldwide, shifts in vegetation communities from grass to shrub dominated have been a major consequence of altered fire regimes, cattle grazing practices, and climate change [Archer et al, 1988; Archer, 1989; Brown and Archer, 1989; Buffington and Herbel, 1965; Van Auken, 2000]. [4] The amplified carbon cycling activity beneath shrubs is due to deposition of high-quality litter on the soil surface, significant growth of woody root biomass, and a favorable (cool, wet) microclimate (fertile island effect) [Belsky, 1994; Hibbard et al, 2001; Liu et al, 2010; McCulley et al, 2004; Schlesinger et al, 1996; Villegas et al, 2010a, 2010b; Zou et al, 2007] These factors lead to the development of large soil microbial communities [Cable et al, 2009]. [7] The goal of this study is to quantify the microsite-specificity of soil respiration “characteristics” (i.e., microclimatic effects on the rate magnitude and water and temperature sensitivities) in a semiarid riparian ecosystem experiencing shrub encroachment Understanding these patterns is critical for scaling plot to ecosystem-scale CO2 effluxes and for better predicting changes in soil carbon dynamics with shrub expansion and climate change. This analysis approach allowed for seamless integration of the two data sets, and the incubation data were used to help inform the temperature sensitivity parameters in the respiration model
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
