Restoration and Recovery of Soil Microbial Activities Following Disturbances in Drylands: Mining, Warming and Wildfire

Abstract

Drylands cover a large portion (approximately 40%) of the Earth’s land area and are under expanding pressures to provide ecosystem services for a growing population, which results in significant disturbance to soils and soil degradation. Disturbance to dryland soils may come from land use changes such as mining, environmental changes such as climate warming and ecosystem regime changes such as increased wildfire frequency and severity. These disturbances negatively impact numerous critical soil functions, including site productivity, soil carbon storage and cycling, and ecohydrological dynamics, the restoration of which requires an understanding of microbial processes that may regulate these functions. This dissertation examines the response of microbial activities to these differing examples of dryland disturbances and their role in the restoration or natural recovery of the critical soil functions described above. I first evaluated the effects of three candidate restoration amendments (woodchips applied at the surface, woodchips incorporated into the soil and biochar incorporated into the soil) on soil carbon dynamics and microbial activities as well as plant cover in disturbed soils. I found the most beneficial effects on extracellular enzyme activities and soil carbon resulted from surface-applied woodchips, while woodchips incorporated into the soil may increase heterotrophic soil efflux of CO2 and soil carbon loss, adversely affecting the restoration of critical soil functions. Following this study, I evaluated the potential influence of prolonged warming on the microbial responses to these restoration amendments. I found that responses to warming in drylands may be limited, and therefore the beneficial outcomes of surface-applied woodchip restoration amendments may remain useful under warmer conditions. Finally, using a 30-year chronosequence of fire in the Rocky Mountains of Colorado, I evaluated the degree and persistence of the effects of high severity fire disturbance on extracellular enzymes and the relationship between extracellular enzyme activities and critical soil functions. We found a persistent long-term negative effect of high severity fire on soil extracellular enzyme activities and that recovery of vegetation and subsequent carbon inputs to soil are a key component of extracellular enzyme recovery. Taken together, this research provides evidence that evaluating microbial responses to restoration or recovery of soils can contribute to our understanding of the success of restoration activities and natural recovery of dryland soil.