Enhancing the relationship between biodiversity and ecosystem functioning under multiple anthropogenic stressors

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Biodiversity is the cornerstone of healthy ecosystem functioning and the delivery of benefits to human populations, and higher biodiversity has been shown to result in greater functioning. These biodiversity-ecosystem function (BEF) relationships have been repeatedly observed, yet, we actually have very little understanding about how anthropogenic stressors and ecosystem modifications influence BEF relationships. In human-dominated landscapes, stressors influence fundamental abiotic components of an ecosystem, such as nutrient availability, the flow of water, temperature fluctuations, soil fertility, the pH and salinity of soil and water. These anthropogenic influences also include the biotic components like the presence and spread of non-indigenous species, as well as the exclusion of large-bodied and long-lived organisms. While these novel ecosystems undeniably supply important functions and benefits to people, it remains unclear if increasing biodiversity in these systems provides the same return as in natural ecosystems. Anthropogenic stressors can act synergistically or antagonistically in influencing BEF relationships because they can impact individual species in a multitude of ways that can alter species coexistence and fitness. In plant ecosystems, these stressors can have three main effects: 1) a direct reduction of species fitness -thus reducing their competitive abilities; 2) an alteration of niche spaces that allow species to coexist; and 3) a disruption of species-specific interactions like pollination mutualisms or soil pathogens. To understand the impacts of anthropogenic stressors on BEF relationships, I will carry out a number of studies examining species performance, coexistence, community diversity and ecosystem function and then compare these to combinations of stressors. Observational studies will use real-world stressor gradients of urbanization, species invasion, chemical and road salt pollution, and soil fertility to evaluate BEF relationships in urban settings. Simulations will specifically assess assumptions about direct and indirect impacts of stressors on species and how increasing diversity influences functioning as competition and coexistence are impacted. This work will focus on the prevalence of stressor impacts on belowground plant-soil feedbacks and how stressors alter mutualistic associations, and further how these associations influence plant fitness and coexistence. Material from the observational studies will be used to initiate experiments, for example as stressor-influenced pools of soil microbes for pot experiments. Experiments will use growth chambers and field plots to factorially combine richness and stressor treatments to test whether increasing numbers of stressors reduce the strength of BEF relationships or whether diversity is increasingly important for maintaining function under multiple stressors.