Maintaining soil carbon in semiarid meadows: inputs, retention, and resulting carbon stocks

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Morra, Brian Matthew

Issue Date

2022

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Dissertation

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Climate Change , Hydrology , Restoration , Soil Carbon

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Soil carbon (C) provides ecosystem services and can function as a C sink to mitigate climate change. Soil C is the result of inputs facilitated by autotrophs and respiratory losses caused by heterotrophic soil microbes. Inputs and outputs occur unevenly across the landscape creating soil C hotspots such as meadows and riparian areas. Maintaining soil C and the associated ecosystem services requires consideration of how annual weather, plant communities, edaphic characteristics, and land use interact to change the magnitude of annual C inputs and outputs. My dissertation considers the impact of these factors on annual C inputs to soils of grazed meadows in central Nevada, and the retention of C sorbed to mineral surfaces from meadows across climates. Applying insights gained from studying C inputs and outputs to management, I also present the impact of grazing management on soil and ecosystem C stocks following 27 years of grazing management. My results show that semiarid meadows have large gross inputs (580 ± 103 g C m-2 y-1) that can be comparable to more humid ecosystems such as Mediterranean grasslands (639 ± 210 g C m-2). These large inputs are likely driven by driven by antecedent root mass which is incorporated into soil C stocks consistently among years, plant communities and grazing intensities. Under years of below average precipitation, inputs to soils decreased most with high grazing intensity and remained constant where grazing was eliminated. In meadows located in humid and semiarid climates, the retention of C inputs sorbed to mineral surfaces of meadow soils is greatest in regions with high productivity. This may be due to microbial use of mineral sorbed C occurring under low productivity conditions. This work shows that grazing management consisting of grazing exclusion or changes to the timing and intensity of grazing is an effective tool to increase C inputs to soils, resulting annual gains of ecosystem C ranging from 80 to 303 g C m-2 annually. The impact of grazing management in riparian ecosystems can increase C stocks on geomorphic surfaces extending from the stream channel the valley edge. My dissertation shows that meadows and riparian ecosystems found in semiarid ecosystems have the potential to be large C sinks while still providing resources for grazing. Management that considers annual weather, hydrology, and plant productivity can contribute to the recovery and retention of C contained in these ecosystems.

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