TY - JOUR
T1 - Shrub influence on soil carbon and nitrogen in a semi-arid grassland is mediated by precipitation and largely insensitive to livestock grazing
AU - Throop, Heather L.
AU - Munson, Seth
AU - Hornslein, Nicole
AU - McClaran, Mitchel P.
N1 - Funding Information:
This research was supported by US National Science Foundation DEB 0953864, Arizona State University, University of Arizona, Arizona Experiment Station, and the U.S. Geological Survey Ecosystems Mission Area. Grazing data sets were provided by the Santa Rita Experimental Range Digital Database (https://cals.arizona.edu/srer/data.html). Funding for the digitization of these data was provided by USDA Forest Service Rocky Mountain Research Station and the University of Arizona. We thank K. Landreville, E. Benites, and M. Farrell for field data collection, soil sampling, and laboratory assistance. Any use of trade, product, or firm names in this paper is for descriptive purposes only and does not imply endorsement by the US Government.
Publisher Copyright:
© 2021 Taylor & Francis Group, LLC.
PY - 2022
Y1 - 2022
N2 - Dryland (arid and semi-arid) ecosystems globally provide more than half of livestock production and store roughly one-third of soil organic carbon (SOC). Biogeochemical pools are changing due to shrub encroachment, livestock grazing, and climate change. We assessed how vegetation microsite, grazing, and precipitation interacted to affect SOC and total nitrogen (TN) at a site with long-term grazing manipulations and well-described patterns of shrub encroachment across elevation and mean annual precipitation (MAP) gradients. We analyzed SOC and TN in the context of vegetation cover at ungrazed locations within livestock exclosures, high-intensity grazing locations near water sources, and moderate-intensity grazing locations away from water. SOC was enhanced by MAP (p < 0.0001), but grazing intensity had little effect regardless of MAP (p = 0.12). Shrubs enhanced SOC (300–1279 g C m−2) and TN (27–122 g N m−2), except at high MAP where the contribution or stabilization of shrub inputs relative to grassland inputs was likely diminished. Cover of perennial herbaceous plants and litter were significant predictors of SOC (r 2 = 0.63 and 0.34, respectively) and TN (r 2 = 0.64 and 0.30, respectively). Our results suggest that continued shrub encroachment in drylands can increase SOC storage when grass production remains high, although this response may saturate with higher MAP. In contrast, grazing–at least at the intensities of our sites–has a lesser effect. These effects underscore the need to understand how future climate and grazing may interact to influence dryland biogeochemical cycling.
AB - Dryland (arid and semi-arid) ecosystems globally provide more than half of livestock production and store roughly one-third of soil organic carbon (SOC). Biogeochemical pools are changing due to shrub encroachment, livestock grazing, and climate change. We assessed how vegetation microsite, grazing, and precipitation interacted to affect SOC and total nitrogen (TN) at a site with long-term grazing manipulations and well-described patterns of shrub encroachment across elevation and mean annual precipitation (MAP) gradients. We analyzed SOC and TN in the context of vegetation cover at ungrazed locations within livestock exclosures, high-intensity grazing locations near water sources, and moderate-intensity grazing locations away from water. SOC was enhanced by MAP (p < 0.0001), but grazing intensity had little effect regardless of MAP (p = 0.12). Shrubs enhanced SOC (300–1279 g C m−2) and TN (27–122 g N m−2), except at high MAP where the contribution or stabilization of shrub inputs relative to grassland inputs was likely diminished. Cover of perennial herbaceous plants and litter were significant predictors of SOC (r 2 = 0.63 and 0.34, respectively) and TN (r 2 = 0.64 and 0.30, respectively). Our results suggest that continued shrub encroachment in drylands can increase SOC storage when grass production remains high, although this response may saturate with higher MAP. In contrast, grazing–at least at the intensities of our sites–has a lesser effect. These effects underscore the need to understand how future climate and grazing may interact to influence dryland biogeochemical cycling.
KW - Bush encroachment
KW - Prosopis
KW - dryland
KW - piosphere
KW - precipitation gradient
KW - soil organic carbon
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U2 - 10.1080/15324982.2021.1952660
DO - 10.1080/15324982.2021.1952660
M3 - Article
AN - SCOPUS:85111350368
SN - 1532-4982
VL - 36
SP - 27
EP - 46
JO - Arid Land Research and Management
JF - Arid Land Research and Management
IS - 1
ER -