Biocrust disturbance decreased cyanobacteria, increased fungi, and altered shrubland and grassland nitrogen pools

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Eva Stricker, Jennifer A. Rudgers and Vanessa Fernandes, Department of Biology, University of New Mexico, Albuquerque, NM, Rose Adelizzi, Biology & Environmental Science/Studies, Washington College, Chestertown, MD, E. a. O'brien, Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, Mikaela Hoellrich, Department of Plant and Environmental Science, New Mexico State University, Las Cruces, NM, Michael Mann, Biology, University of New Mexico, Albuquerque, NM, Anthony Darrouzet-Nardi, Biological Sciences, University of Texas at El Paso, El Paso, TX

Background/Question/Methods
Interactions between plants and soil microbes influence plant nutrient transformations, including nitrogen (N) fixation, nutrient mineralization, and resource exchanges through fungal networks. Physical disturbances to soils can disrupt soil microbes and associated processes that support productivity. In low resource drylands, biological soil crusts (“biocrusts”) occupy surface soils and house key autotrophic and diazotrophic microbes. Disturbances to biocrusts may alter interactions among biocrusts, plants, and fungal networks that are hypothesized to drive carbon and nutrient dynamics; however, comparisons across ecosystems are needed to generalize how soil disturbances alter microbial communities and their contributions to N pools and transformations. To evaluate linkages among plants, fungi, and biocrusts, we mimicked footfall disturbances by stomping cyanobacteria-dominated biocrusts in Chihuahuan Desert grassland and shrubland ecosystems.
Results/Conclusions
Stomping decreased total cyanobacteria and N fixer abundances by >77% and chlorophyll a by up to 55%, and conversely, increased soil fungal abundance by 50% compared to controls. Responses of root-associated fungi differed between the plant species and ecosystem types, with a maximum of 80% more aseptate hyphae in stomped than control plots. Although stomping did not affect 15N tracer transfer from biocrusts to the dominant grass, Bouteloua eriopoda, stomping increased available soil N by 65% in the shrubland, and decreased leaf N of B. eriopoda up to 16%. Altogether, these results demonstrate that disturbances to soil microbial communities have potential to cause substantial, but ecosystem-specific, changes in N transformations by reducing and reordering biocrust taxa.