Dimensions US-China: Collaborative Research: Quantifying the Impact of Eutrophication on the World's Grassland Soil Microbial Biodiversity and Functioning

Human activities are increasing the amount of biologically limiting nutrients, such nitrogen (N) and phosphorus (P), flowing into ecosystems on every continent, and this increased nutrient supply is causing dramatic impacts such as biodiversity loss. Microbes comprise most of the biodiversity on earth, and the diversity of microbes in the soil is a critical link in maintaining the health of our ecosystems. However, we have little understanding of how alteration of global nutrient supplies are affecting soil microbial diversity. The proposed work will quantify how increased nutrient supplies affect soil microbial diversity and how these changes affect the functioning of grassland ecosystems around the world. The research will leverage a worldwide network of scientists, the Nutrient Network (NutNet), who are replicationg an identical nutrient-addition experiment at more than 100 grassland sites across 26 countries. Using this global research platform, this project will explore different 'diversities' of the soil microbes by counting their idenities (taxonomic diversity, TD), their evolutionary relationships (phylogenetic diversity, PD), the genes encoded in their DNA (genetic diversity, GD), and what they are doing (functional diversity, FD). The scientists on this research team will not only determine how these different dimensions of diversity respond to the nutrient change but also why they are changing. Are microbial communities changing because some microbes can grow better (abiotic filtering), compete or cooperate with other microbes or plants (biotic interactions), or are good or bad at migration (dispersal), or appear by chance (drift)? This project will develop new mathematical models to predict how nutrients change the diversity of soil microbes and their functions in different regions in the future. Broader impacts of this project include (i) increased public engagement and literacy in STEM via K12 education that will reach over 4,000 K-12 students including from under-served schools using NutNet plots set up for education at Cedar Creek and activities at Oklahoma; (ii) enhanced research infrastructure of the global NutNet collaboration, which benefits the greater research community via published data, provision of samples, and space for additional projects; and (iii) advanced training in international cross-disciplinary collaboration for project post-docs and students, that will generate a more competitive workforce to engage in systems-level problem solving for agriculture, environment, ecology and climate research.

The project will use high throughput metagenomics technologies and integrative mathematical and statistical modeling to analyze soil grassland microbial diversity responses to experimental eutrophication along global gradients in climate, plant diversity, and edaphic conditions. The research will test theory-based predictions about the responses of soil microbes to nutrient supply across scales of space and time, generating novel insights into: (i) global patterns of soil microbial biodiversity (TD, PD, GD, FD) along broad gradients of climate, plant diversity, and edaphic conditions; (ii) the context-dependence and interactive effects of N and P supply on grassland soil microbial communities, nutrients, and soil C storage; (iii) the importance of plant, microbe and soil elemental stoichiometry for controlling the responses of microbial biodiversity and functioning to nutrient supply, as well as the role of plant-microbe interactions in mediating plant responses to nutrient addition; (iv) the relative importance of stochastic (e.g., dispersal) and deterministic (e.g., abiotic filtering, biotic interactions) processes controlling responses by each of the dimensions of microbial biodiversity to nutrient addition across global environmental and geographic gradients; (v) the importance of biodiversity and community assembly in controlling soil microbial ecosystem functioning, and the influence of environmental factors (e.g., soil, plant, climate, geography); (vi) potential 'biomarkers' (key taxa or genes) of grassland soil functions; (vii) novel metagenomics-enabled ecosystem models for global simulation of grassland soil C dynamics; and (viii) model-inferred impacts of nutrient addition on soil C dynamics across biogeographic gradients in climate, plants and edaphic conditions.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.