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Lancaster University (2020)

Soil microbial attributes and function across multiple scales in Neotropical Savanna

Siewerding Meirelles, Gabriela

Titre : Soil microbial attributes and function across multiple scales in Neotropical Savanna

Auteur : Siewerding Meirelles, Gabriela

Université de soutenance : Lancaster University dual Universidade Federal de Lavras, Brazil

Grade : Doctor of Philosophy 2020

Savannas are the most sensitive ecosystems to future changes in land use and climate. Therefore, understanding of the factors underpinning savanna ecosystem function is urgently required for ecologically-relevant conservation and management. This thesis aims to address this knowledge gap, investigating how local conditions and landscape features influence soil microbial attributes, and the resistance and resilience of soil functioning within the three distinct vegetation types of the Brazillian Cerrado biome : Gallery forest, Veredas and Cerrado sensu stricto. Firstly, I evaluated how local vegetation characteristics and soil physico-chemical properties interact and influence soil microbial attributes (Chapter 2). Secondly, I investigated how landscape-scale anthropogenic disturbance and topography affect soil microbial community structure and enzyme activity (Chapter 3). I also assessed how soil CO2 emissions are related to microbial attributes and topography, and the resistance and resilience of soil functioning (respiration) of the vegetation types in response to drought and drying-rewetting (Chapter 4). Lastly, I conducted an experiment to investigate the mechanisms underpinning C mineralisation in rewetted soils from the different Cerrado vegetation types (Chapter 5). At the local scale, I found different patterns in above- and below-ground interactions within the three vegetation types. Soil physico-chemical properties strongly affected soil microbial attributes in Gallery forests and Veredas, whereas vegetation characteristics were the main determinant in Cerrado sensu stricto. At the landscape scale, I found topography to be the major predictor of microbial attributes in all vegetation types, and that anthropogenic disturbance influences soil microbial communities both positively and negatively. Veredas soils were the most resistant to drought, while Gallery forests soils were the most resilient in their reponse to rewetting after drought. I also discovered that soil organic matter quality combined with nutrient availability influenced different mechanisms underpinning soil C stock and release to the atmosphere across the different Cerrado types. Based on these findings, I discuss the importance of flooding regimes in the wetland vegetation types (Gallery forest and Veredas) for ecosystem functioning, and implications for future land-use and climate change in the Cerrado biome (Chapter 5). I emphasize the need for Brazilian environmental legislation to prioritize the integral conservation of periodically flooded areas.


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