Carbon dynamics and earthworm populations in grassland ecosystems of the Palouse region.

摘要

Understanding the effects of management practices, soil organisms and soil properties on carbon sequestration and biodiversity conservation was the main focus of the research projects presented in this dissertation. I measured and compared carbon pools and processes in two important grassland ecosystems of the Palouse region of southeastern Washington and northern Idaho: native prairie remnants and Conservation Reserve Program (CRP) set-asides. I found that carbon inputs were similar between prairie and CRP grasslands. However, root biomass and soil carbon concentrations were higher in prairie remnants. These results demonstrate that processes and carbon inputs in CRP sites have reached similar levels to native prairies, but belowground carbon pools are still larger in prairie remnants. The results suggest that efforts to promote carbon sequestration in these grasslands should be focused on increasing belowground carbon. I also characterized earthworm populations in native prairie remnants and CRP set-asides. I found that earthworm populations were composed mostly of European exotic earthworms in both grassland types and dominated by the exotic earthworm Aporrectodea trapezoides. A single specimen of the native earthworm, Driloleirus americanus was found at a prairie remnant. The results suggest that conservation priorities for native earthworms in the Palouse need to focus on habitat description, conservation and possibly restoration. Additionally, I measured the effect of the exotic-invasive earthworm Aporrectodea trapezoides on carbon dynamics using a microcosm experiment. I found that the presence of A. trapezoides did not have an effect on plant productivity, and that its main impact on carbon dynamics was through the formation of soil macroaggregates. These macroaggregates can physically protect carbon against mineralization. An additional collaborative study aimed at describing soil and site correlations with Palouse prairie plant communities confirmed that aspect and vegetation structure were significant predictors of plant species richness (R2 = 0.15) and plant diversity (R2 = 0.13). These results may help set research and biological conservation priorities for isolated and un-inventoried prairie remnants.