What happens to the green stuff? Applying a novel zoogeochemical lens to ecosystem nutrient cycling

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Our project will make a major new contribution to the emerging field of zoogeochemistry as the first study, in any terrestrial ecosystem, to experimental quantify alternative animal-controlled recycling pathways and determine their influence on ecosystem biogeochemistry at a large scale.Biogeochemical cycling, the movement and transformation of chemicals and nutrients in an ecosystem, involves the breakdown of plant matter and is essential for making nutrients available again for plants. Animals directly and indirectly affect elemental cycling, but have typically been overlooked as key agents. Humans are altering biogeochemical cycles through changes to fire regimes, biodiversity and climate change. As such it is essential we understand what biogeochemical pathways operate in different places, and what the consequences of global changes are for biogeochemical functions. For example, what are the impacts of megaherbivore defaunation or restoration on ecosystem nutrient supply? Here, we quantify plant biomass recycling via the two biotically-driven recycling pathways, herbivory and decomposition, and determine their influence on ecosystem biogeochemistry.We focus on an arid savannas where these pathways are dominant and the system is tractable (i.e. uniquely, we can manipulate the dominant decomposer, termites, and also herbivores). Using large-scale field manipulations, we will separate out and quantify the importance of key animal groups (large mammalian herbivores, invertebrates, microbes) for biomass consumption and nutrient recycling. We then determine the consequences of herbivory and decomposition for ecosystem biogeochemistry.There are two work packages (WPs):WP1. Biomass removal in each recycling pathway: dominance, agents & interactions: using targeted suppression methods to reduce the abundance of termites combined with large mammal exclosures we will be partition and quantify the contribution of different pathways and animal groups to biomass removal. We will also explore additive effects and interactions among the pathways, and determine levels of system redundancy (i.e. whether any groups can compensate ecologically for others in their absence).WP2. Contribution of pathways to biogeochemical cycling: we will quantify ecosystem productivity and nutrient cycling to determine the contribution of the different pathways to ecosystem biogeochemical cycling. In doing so we will provide novel assessments of the way savannas function and the contributions that different animal groups make.By using large-scale experimental manipulations to simultaneously determine the relative contribution of two dominant recycling pathways in arid savannas (herbivory and decomposition) and their influence on savanna biogeochemistry, our proposed project will deliver novel and fundamental insights into the functioning of these systems enabling a better understanding of the biogeochemical consequences of altered pathways. This would also be, to our knowledge, the first such experimental quantification of these alternative pathways in any large-scale terrestrial ecosystem.