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Abstract Root production influences carbon and nutrient cycles and subsidizes soil biodiversity. However, the long‐term dynamics and drivers of belowground production are poorly understood for most ecosystems. In drylands, fire, eutrophication, and precipitation regimes could affect not only root production but also how roots track interannual variability in climate.We manipulated the intra‐annual precipitation regime, soil nitrogen, and fire in four common Chihuahuan Desert ecosystem types (three grasslands and one shrubland) in New Mexico, USA, where the 100‐year record indicates both long‐term drying and increasing interannual variability in aridity. First, we evaluated how root production tracked aridity over 10–17 years using climate sensitivity functions, which quantify long‐term, nonlinear relationships between biological processes and climate. Next, we determined the degree to which perturbations by fire, nitrogen addition or intra‐annual rainfall altered the sensitivity of root production to both mean and interannual variability in aridity.All ecosystems had nonlinear climate sensitivities that predicted declines in production with increases in the interannual variance of aridity. However, root production was the most sensitive to aridity in Chihuahuan Desert shrubland, with reduced production under drier and more variable aridity.Among the perturbations, only fire altered the sensitivity of root production to aridity. Root production was more than twice as sensitive to declines with aridity following prescribed fire than in unburned conditions. Neither the intra‐annual seasonal rainfall regime nor chronic nitrogen fertilization altered the sensitivity of roots to aridity.Synthesis. Our results yield new insight into how dryland plant roots respond to climate change. Our comparison of dryland ecosystems of the northern Chihuahuan Desert predicted that root production in shrublands would be more sensitive to future climates that are drier and more variable than root production in dry grasslands. Field manipulations revealed that fire could amplify the climate sensitivity of dry grassland root production, but in contrast, the climate sensitivity of root production was largely resistant to changes in the seasonal rainfall regime or increased soil fertilization.
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Long-term dynamics of soil organic matter and aboveground net primary production in a Chihuahuan Desert Grassland at the Sevilleta National Wildlife Refuge, New Mexico (1989-2014)
Drylands contain a third of the organic carbon stored in global soils; however, the long-term dynamics of soil organic carbon and soil organic matter (SOM) in drylands remain poorly understood relative to dynamics of the vegetation carbon pool. We examined long-term patterns in SOM against both climate and prescribed fire in a Chihuahuan Desert grassland in central New Mexico, USA. SOM was measured each spring and fall for 25 years (1989–2014) in unburned desert grassland and from 2003 to 2014 following a prescribed fire. SOM concentration from 0-20 cm depth did not show a clear long-term trend but fluctuated seasonally at both burned and unburned sites, ranging from a minimum of 0.9% to a maximum of 3.3%. SOM concentration declined nonlinearly in wet seasons and peaked in dry seasons. These results not only contrast with the positive relationships between aboveground net primary production and precipitation for this region, but also with previous reports of greater SOM in wetter sites across drylands globally, suggesting that space is not a good substitute for time in predicting the dynamics of dryland SOM. We suggest that declines in SOM in wet periods are caused by increased soil respiration, runoff, leaching, and soil erosion. In addition to tracking natural variability in climate, SOM concentration also decreased by 14% following prescribed fire, a response that magnified over time and has persisted for nearly a decade due to the slow recovery of primary production. Our results document the surprisingly dynamic nature of soil organic matter and its high sensitivity to climate and fire in this dryland ecosystem.
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- Award ID(s):
- 1655499
- PAR ID:
- 10424138
- Publisher / Repository:
- Environmental Data Initiative
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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