Testing the Fungal Loop Hypothesis
My first major project at UTEP was an examination of the role of fungi and biocrusts in transporting nutrients in dryland soils. We used methods such as isotopic tracers to follow nitrogen through biocrusts, hyphae, and roots as well as performing experimental manipulations of the fungi, the nutrients, and other aspects of the system. In the end, we found less evidence than we expected for the fungal loop hypothesis but learned a lot about how N moves through surface soils.

Key papers: Are fungal networks key?; Vertical movement of nutrients

Climate change in dryland ecosystems
Just before I came to UTEP, I worked on biological soil crust (biocrust) responses to elevated temperature and changing precipitation. Our analyses of the net exchange of carbon between biocrusts and the atmosphere in a multiyear 2°C warming experiment (infrared heat lamps) showed increased carbon losses in the warming treatment, suggesting negative impacts of warmer future climates on biocrusts. We also discovered these crusts can perform photosynthesis under snow despite living in the desert.

Key papers: Net soil exchange (NSE) of CO2; Long-term warming effects on CO2 efflux

Changing seasonality of plant-soil interactions in the Arctic tundra
Arctic soils contain large stocks of carbon and may be a significant CO2 source in response to climate change. Using an early-snowmelt×warming manipulation at a site near Toolik Field Station on Alaska's North Slope, our team investigated changes in soil nutrient cycling in response to changing climate and seasonality. Our results showed that snowmelt acceleration causes more rapid early-season nutrient immobilization in soils and that early snowmelt in unwarmed plots can cause season-long reductions in root growth and inorganic N availability due to plant exposure to harsh conditions in the absence of snow.

Key papers: Early snowmelt effects; Spatially inaccessible labile N

Landscape heterogeneity of nitrogen cycling in an alpine-subalpine ecosystem (Dissertation)
Microbially mediated nitrogen cycling rates are heterogeneous across landscapes, with disproportionate activity occurring in biogeochemical hot spots. My dissertation examined landscape heterogeneity in soil nitrogen (N) cycling pools and fluxes in a 0.89 km2 site at the alpine-subalpine ecotone. My data showed that a large percentage of total inorganic N pool sizes and associated cycling rates were attributable to a small percentage of hot spots. We also discovered a spatially inverse relationship between atmospheric N deposition and N-fixing plant abundance.

Key papers: Nitrogen hot spots; N deposition reduces soil buffering

Sagebrush encroachment in subalpine meadows of the Sierra Nevada Mountains
Over the last 100 years, sagebrush shrubs (Artemisia rothrockii) have encroached into subalpine meadows in the Sierra Nevada Mountains due to groundwater decline associated with livestock grazing. We discovered that sagebrush transpiration does not dry out the soil during encroachment as we hypothesized it might. Using stable oxygen isotopes, we also showed that both young sagebrush plants and resident herbs used shallow soil water but were also able to access deeper water. Nutrient cycling rates increased with shrub encroachment.

Key papers: Effects of young sagebrush shrubs; Depth of water acquisition