How does elevation and/or substrate affect the composition of biocrusts?

Biocrusts are important organisms in drylands, performing several ecological functions. Higher elevations are typically associated with higher amounts of precipitation which can allow for vascular plants to thrive. This can either outcompete the biocrusts or alternatively, provide optimal conditions for later successional biocrust communities including lichens and mosses. While there may be a clear relationship between the abundance of biocrust and elevation, this may be obscured by soil type.

Bulk soil and biocrust samples were collected from a variety of sites (n=13) along an elevational gradient roughly between Phoenix (300 m) and Flagstaff (2,100 m) while targeting different soil types such as granite, limestone, sandstone, mixed alluvium and basalt. The purpose of this study was to determine the effect of parent material and elevation on biocrust communities throughout Arizona. This is the first broad scale, systematic study to our knowledge to examine the effect of both elevation and soil type on the abundance and diversity of biocrusts.

We used a 1x1 m plot to measure % cover of biocrusts which were later identified in the lab to the lowest possible taxonomic group. The enzymatic activity of 3 enzymes (ß-glucosidase, phosphatase and urease) was also measured using a high-throughput, fluorometric approach. Other response variables include soil respiration, microbial biomass, soil organic carbon, electrical conductivity, chlorophyll a, water holding capacity, bulk density, soil pH, soil color and soil texture.

We found the highest biocrust abundance on gypsum soil at moderate elevation while the lowest biocrust cover recorded was on basalt soil at high elevation. Lichens and mosses occurred more at higher elevations. Enzyme activity is expected to be greater at higher elevations where more precipitation occurs. These measurements will provide knowledge about the nutrient cycling in arid lands where nutrients and precipitation are limited and unpredictable.