Biocrusts are complex communities of microorganisms with many important functions in dryland systems including soil stabilization. Prior work indicates that after human disturbance, biocrust recovery rates are highly variable and dependent on biotic and abiotic factors. One barrier to biocrust recovery in restoration settings is microbial propagule availability. Propagule dispersion is hypothesized to occur in three ways: 1) propagules move from mature biocrusts to bare soil via lateral growth, 2) propagules disperse by aeolian processes, 3) propagules travel to bare soil during overland rainfall events. Propagule limitation may be magnified by the size of the disturbance at the soil surface. To test these hypotheses, mature biocrusts on the Colorado Plateau were scraped off soil surfaces in four differently sized plots at two separate sites: 1x1 m, 50 x 50 cm, 25 x 25 cm, and 10 x 10 cm (n=6). Biocrusts were left alone for two years to naturally recover. Plots were then assessed for soil stability, level of development, recovered surface area, photosynthetic potential, and microbial abundance along transects through the middle of each plot to determine differences in recovery over the two-year period.
Results/Conclusions
After two years, 81% of sampled points exhibited high soil stability (stability of 5-6 on a standard scale ranging from 1 to 6), while 76% of points had recovered a light to dark cyanobacterial crust (level of development of 2 or 3). The two sites did not show significant differences in recovery over this time period despite differences in soil texture which are known to play important roles in recovery rates. There were no differences in the level of development or soil stability measures for plots of different sizes; we saw equivalent recovery in plots that were 1 x 1 m in size and plots that were 10 x 10 cm in size. Additionally, the pattern of recovery did not follow expected trends for lateral dispersion of microbial propagules from the edges of scraped plots toward the center. Instead, there was a random arrangement of soil recovery due to microbial growth that is more in line with aeolian deposition or overland flow. These results indicate that after disturbance on the Colorado Plateau, microbial limitation in recovering soils may be controlled by a combination of the rate of aeolian deposition and pattern of overland flow events. These findings inform dryland restoration projects that aim to restore soil stability at a site through manipulation of biocrust communities.