Responses to Biocrust Restoration and the Role of Cyanobacterial Exopolysaccharides in Dryland Ecosystems

Publication Year:
2017
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Repository URL:
https://scholar.colorado.edu/ebio_gradetds/98
Author(s):
Chock, Taylor Mei Hop
Tags:
biological soil crusts; cyanobacteria; drylands; ecosystem function; exopolysaccharides; restoration; Biology; Ecology and Evolutionary Biology; Environmental Monitoring
thesis / dissertation description
Anthropogenic land use and changes in climate can cause severe degradation in dryland ecosystems, leading to the loss of ecosystem functioning and services. Thus, restoring ecosystem function in these already low productivity areas is critical. Biological soil crusts (biocrusts) are soil surface communities of cyanobacteria, lichens, mosses, and other microorganisms that play key roles in dryland ecosystem functions, making them excellent targets for dryland restoration. In this study, we addressed ecosystem barriers to successful biocrust rehabilitation - propagule scarcity, resource limitation, and soil stability - with treatments of inoculation, shading, and an artificial polyacrylamide soil stabilizer in the Great Basin Desert. Combinations of these treatments were also implemented to address the possibility of multiple barriers. All experimental treatments were implemented on clay and sandy clay loam (SCL) soils and monitored annually for three years. We found that overall biocrust recovery was much faster on clay soil, and that soil type influenced treatment efficacies. On clay soil, the combination of shade+inoculum was the most successful in promoting biocrust recovery, while on SCL soils, a low inoculation level was sufficient. Although identifying effective restoration treatments is a critical step in biocrust restoration, mechanisms underlying ecosystem functions and what functional groups of microorganisms contribute to these functions also need to be better understood. To try to understand this, we explored how cyanobacterial exopolysaccharides (EPSs) affected soil stability and hydrology to see if EPSs could be used as proxies for these functions. We found that EPSs were more important to soil stability on less stable SCL soils than on clay soils, implying that other contributing factors need to be considered on finer soil types. Finally, we observed shifts in microbial communities over time following an inoculum restoration treatment to more abundant later-successional, dark cyanobacteria species, reflecting patterns seen in natural recovery. However, microbial communities of restored plots were still distinct from mature crusts after three years. Findings from this study can be applied to dryland ecosystem management. Biocrust restoration efforts should focus on coarser soil types since finer soil types recover faster naturally. However feasibility, cost, and time to implement restoration treatments should be carefully considered when scaling up to a landscape level. Biocrust disturbance mitigation should also be prioritized as biocrusts take a long time to recover, even following the most effective restoration methods.