Biological soil crusts (‘biocrusts’) are communities of microorganisms that develop on soil surfaces and are an important functional component of dryland systems. Biocrusts are highly susceptible to soil surface disturbance such as those generated from human activities. Due to the importance of biocrust communities to the ecological functioning of dryland ecosystems there is keen interest in restoration of these communities after disturbance. Here we report on biocrust inoculum development and successful inoculum application methods in a series of field experiments. This work was carried out at cool (Great Basin) and hot (Chihuahuan) desert sites. Biocrust inoculum was developed from two sources: locally-collected biocrust (LB) organisms and mixed isolates (MI) of the major pioneer cyanobacteria. In developing biocrust inoculum we addressed these questions: What are the key resource constraints to enhancing the biomass of local field-collected biocrusts and lab-reared biocrust inoculum and how do we overcome these constraints to provide an adequate supply of inoculum for biocrust restoration? In a series of field experiments we addressed the question, how can inoculum levels, availability of limiting resources for biocrust growth, and habitat be modified to enhance the potential for biocrust growth and restoration success under a field setting?
Biocrust biomass from LB responded positively to reductions in light, additions of nutrients, and water pulses with intermittent drying periods. LB biocrust biomass increased 50 – 100 fold over a 12-week time period. Scaling up early pioneer MI in liquid media was adequate for all of the early pioneer cyanobacteria with the exception of Microcoleus spp. Additional methods of inoculating Microcoleus spp onto filter paper was required for this genus. In the field experiments, even the lowest inoculum levels resulted in significant increases in biocrust biomass at the cool desert site. Due to issues of highly mobile soils and overland flow, biocrust recovery at our hot desert site was low. In our cool desert site, biocrusts recovery responded positively to shading, water additions, and soil stabilization strategies (polyacrylamide application and straw checkerboard). Once disturbed, recovery times of biocrust communities may take decades to centuries. Our biocrust inoculum development results show that the biomass of native biocrust organisms can be quickly scaled up in the lab. We also show that at the cool desert site that modifying the habitat in a way that promotes soil stability and reduces water stress promotes the most rapid recovery of biocrusts even at low levels of inoculum.