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Organized Oral Session

Session: : Ecological Islands of the Southwest: Exploring How Theoretical Islands Connect Mountains, Cities, Restoration Strategies and Biogeochemical Cycling in America's Southwest

OOS 54-1 - Drought and land-use change alter fertile island effects on soil biogeochemistry across North American deserts

Thursday, August 10, 2023
10:00 AM – 10:15 AM PDT
Location: 254
Drylands provide vital services for billions of inhabitants and are a central driver of the global carbon (C) cycle. Due to low water and resource availability, drylands are vulnerable to increasing human disturbance, climate warming, and drought, but large uncertainties remain about the consequences of global change for dryland biogeochemistry. One key challenge to understanding and predicting global change consequences in drylands is high biogeochemical heterogeneity at regional and fine spatial scales. The western US, for example, encompasses diverse systems across broad climatic and land use gradients. Within these systems, patchy vegetation supports the creation of “fertile islands,” overlying additional heterogeneity. We examined the effects of drought and physical disturbance in a full factorial design (n=10) across a climatic gradient of 3 North American deserts, using rainout shelters to mimic 100-year drought conditions and a spiked drum aerator to mimic the fracturing and compression of physical disturbance. We analyzed soil from beneath shrubs and in shrub interspaces prior to treatments and for two years post-treatment for numerous C, nitrogen (N), and phosphorus (P) metrics, including total, available, and microbial pools. We predicted that fertile island effects would increase with aridity across sites and that physical disturbance would decrease fertile island effects while drought exaggerated them. As predicted, fertile island effects were stronger and more consistent in hot deserts (P < 0.05), but treatment effects differed across sites. In hot deserts, drought (but not physical disturbance alone) altered many C, N, and P pools in interspace (but not shrub) soils. In contrast, in our cold desert site, disturbance (but not drought alone) affected soil biogeochemistry in the shrub (but not interspace) soils. This work suggests the strength and direction of drought and physical disturbance effects differ fundamentally with climate and shrub cover.