Elevation and parent material drive biocrust distributions and soil extracellular enzyme activity along a dryland elevation gradient

Abstract

Abstract Background and Aims Climate and soil-related variables are two major environmental factors contributing to the spatial distribution of organisms. Elevational gradients can be used to better understand the climate impacts on natural systems given their tight relationship with temperature and precipitation. Soil variables can be used to explain elevational discrepancies at the small scale as they are important predictors of species-specific niches. Dryland ecosystems provide a unique opportunity to better understand the spatial distributions especially regarding biocrusts, a collection of ecologically important organisms that include lichens, mosses and cyanobacteria, that colonize the soil surface. Methods We sampled biocrusts and bulk soil from 31 sites along a 1,700 m elevation gradient between Phoenix and Flagstaff, Arizona, USA. We explored relationships among biocrust cover, elevation and parent materials including granite, limestone, basalt and sandstone. We also measured extracellular enzyme activity at each site as an index of potential microbial activity. Results Lichens were associated with lower elevations whereas higher moss cover corresponded with higher-elevation limestone sites. We found that elevation and soil parent material had significant effects on enzyme activity, although the direction of the associations differed among enzymes. There was also a significant positive correlation between biocrust cover, electrical conductivity and vascular plant cover. Conclusion Overall, this study represents a general framework for environmental variables affecting biocrust communities in drylands, showing that there is a need to include both elevation and soil parent material within analyses of biocrust cover and type (i.e., lichens and mosses).