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

我们的项目将为新兴的动物地球化学领域做出重大的新贡献，作为在任何陆地生态系统中，实验量化动物控制的替代循环途径并确定其对生态系统生物地球化学的影响的第一个研究。生物地球化学循环，即生态系统中化学物质和营养物质的运动和转化，涉及植物物质的分解，对植物重新获得营养物质至关重要。动物直接和间接地影响元素循环，但通常被忽视的关键因素。人类正在通过改变火灾制度、生物多样性和气候变化来改变生物地球化学循环。因此，我们必须了解生物地球化学途径在不同地方的作用，以及全球变化对生物地球化学功能的影响。例如，大型食草动物退化或恢复对生态系统营养供应的影响是什么？本文通过草食和分解两种生物驱动的循环途径对植物生物量循环进行了量化，并确定了它们对生态系统生物地球化学的影响。我们将重点放在干旱的稀树草原上，在那里这些途径占主导地位，系统是可处理的（即，我们可以独特地操纵主要的分解者，白蚁和食草动物）。通过大规模的野外操作，我们将分离并量化关键动物群体（大型哺乳动物、食草动物、无脊椎动物、微生物）对生物量消耗和养分循环的重要性。然后，我们确定草食和分解对生态系统生物地球化学的影响。有两个工作包：WP1。每个循环途径中的生物质去除：优势，因子和相互作用：使用有针对性的抑制方法来减少白蚁的丰度，并结合大型哺乳动物的暴露，我们将划分和量化不同途径和动物群体对生物质去除的贡献。我们还将探索路径之间的加性效应和相互作用，并确定系统冗余的水平（即，是否有任何群体可以在生态上补偿其他群体的缺失）。途径对生物地球化学循环的贡献：我们将量化生态系统生产力和养分循环，以确定不同途径对生态系统生物地球化学循环的贡献。在此过程中，我们将对稀树草原的功能方式和不同动物群体的贡献提供新的评估。通过使用大规模的实验操作来同时确定干旱稀树草原中两种主要循环途径（草食和分解）的相对贡献及其对稀树草原生物地球化学的影响，我们提出的项目将为这些系统的功能提供新颖和基本的见解，从而更好地理解途径改变的生物地球化学后果。据我们所知，这也是在任何大型陆地生态系统中首次对这些替代途径进行实验量化。

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.