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Quantifying the depth effects of environmental changes on soil structure and organic matter decay across scales in the Anthropocene
Faria Tavares de Souza, Ligia
Faria Tavares de Souza, Ligia
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Abstract
Soils are the largest reservoir of terrestrial organic carbon (C). Changes in soil functioning to different environmental conditions imposed in the Anthropocene may result in CO2 feedbacks to the atmosphere and may further alter ecosystem functioning. Human-induced changes to climate and land use patterns are likely to modify soil features due to accelerated rates of biotic responses to these new environmental forcings. However, the degree to which the interplay between biota and soil processes reverberates with depth and across spatial scales is still poorly understood. In this dissertation, I investigate the imprints of the Anthropocene in soil functioning by connecting the responses of soil physical, biological, and chemical features across spatial and temporal scales. In Chapter 1, I developed a dataset characterizing the temperature sensitivity of a purified, extracellular enzyme across a pH gradient and combined it with published datasets of other two extracellular enzymes to similar simulated environmental conditions to explore the fundamental, biochemical limitations that may alter organic matter (OM) decay and dictate future ecosystem functioning under warming at the global scale. Because the soil’s ability to protect and store C is dependent on OM decomposition processes, in Chapter 2, I investigated the influence of land use change on soil organic C (SOC) depth distributions across a regional climatic gradient. I used two complementary scales to parse the degree to which some ecosystem features, such as rooting abundances and soil structure, modify the transport and, consequently, the persistence of C down-profile. In Chapter 3, I explored the potential pace at which soil structural changes can be observed in response to changes in ecosystem features under extreme moisture conditions. I found that warming has the potential to alter OM decay in ways dependent on soil pH, with potential consequences for ecosystem stoichiometry at the biosphere scale and ultimately affecting the protection of C in soils. I also found that decreases in water availability across a climatic gradient can lead to a decoupling of biogeochemical cycles across depths in native prairie soils, contrary to the more homogenous distributions of SOC in cultivated lands regardless of climate. Differential inputs of SOC throughout soil profiles also modified soil structure in ways important for the flow of solutes and water that drive biogeochemical coupling. In Chapter 3, I found that soil structural changes can be observed across relatively short timescales, such as over one growing season, especially at relatively deeper depths in the subsurface. Combined, these findings illuminate the extent of the combined effects of changes in ecosystem features and edaphic properties at different scales and how they can influence ecosystem functioning in the future. Understanding these responses is critical for investigating the ways in which the Anthropocene has altered soil functioning, and to develop well-informed policies that aim at mitigating the effects of climate change.
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Date
2022-12-31
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University of Kansas
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Keywords
Soil sciences, Ecology, Biogeochemistry, Climate change, Extracellular enzymes, Rooting abundances, Soil organic carbon, Soil structure