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The ecology of natural climate solutions: quantifying soil carbon and biodiversity benefits




McClelland, Shelby C., author
Schipanski, Meagan E., advisor
Cotrufo, M. Francesca, committee member
Dillon, Jasmine, committee member
Paustian, Keith, committee member

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Achieving net zero greenhouse gas emission by 2050 will require simultaneous emissions reductions and carbon dioxide removal from the atmosphere. Natural climate solutions offer the most mature opportunities to remove atmospheric carbon and sequester it in woody biomass and soils but currently these options remain at low levels of adoption in the United States. To increase the uptake of these practices by growers, there needs to be greater confidence in the expected soil carbon benefits and improved understanding of potential environmental tradeoffs from these strategies across management and environmental contexts. This dissertation quantified the influence of management decisions and environmental variables on soil carbon responses under two proposed agricultural natural climate solutions: inclusion of cover crops and additions of organic amendments. The ecological and biodiversity co-benefits under these practices were also examined. Using a meta-analysis approach, the first chapter analyzed soil carbon responses to cover crop management decisions and environmental variables. Across 181 observations of 40 publications from temperate climates, inclusion of cover crops in cropping systems increased soil organic carbon stocks from 0-30 cm by twelve percent relative to a similarly managed system without cover crops. Management and environmental variables were responsible for variation in soil C responses across studies. The second chapter evaluated the application of organic amendments to improved and semi-native pastures at a semi-arid experimental site in northern Colorado. Over eight years and two applications of a high-quality organic amendment, soil organic carbon stocks as quantified by equivalent soil mass increased 0.7 Mg C ha-1 yr-1 from 0-20 cm under the organic amendment in the improved pasture relative to the control. After accounting for the additions of carbon from the two amendment applications, soil organic carbon stocks in the improved pasture increased by 0.46 Mg C ha-1 yr-1 from 0-20 cm. In contrast, there was no net change of soil carbon stocks in the semi-native pasture. The third chapter examined changes in plant and soil community composition and function after nitrogen application at the same experimental site. A single organic nitrogen addition to the improved pasture increased forage production, plant diversity, and soil microbial community composition and function. The stronger initial plant responses and the gradual change in microbial community composition and function suggests a plant-mediated response to organic nitrogen in this system, which likely impacted soil carbon cycling. Water-limited, semi-native pastures appear to be more resistant to change under one-time organic and inorganic nitrogen additions than irrigated, improved pastures. The final chapter of this dissertation compared two recommended approaches by the Food and Agriculture Organization of the United Nations for quantifying livestock production system impacts on biodiversity. The results illustrated how indicator selection and functional unit may result in discrepancies between the two methods. Together, these findings contribute to a growing body of scientific evidence in support of natural climate solutions for their climate and environmental co-benefits.


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soil organic carbon
natural climate solutions


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