Harnessing biological complexity to improve food security: How do mycorrhizal networks control resource transfer and plant productivity in inter- and mono-crop model systems?

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A long tradition of research suggests that exchange of resources between plants and their fungal symbionts in linked networks in the soil can increase the resilience of ecosystems to environmental change. There is growing interest in harnessing the resilience building power of these networks of plant and fungi to enhance the sustainability of ecosystems that are managed for food production, but progress in this field has been hindered by difficulties in understanding complex network behaviors that arise from different plant and fungal communities, especially when under stress. This project will address this challenge by combining field experiments, laboratory studies, and mathematical models to quantitatively characterize the exchange of carbon and nitrogen in networks of prairie and pasture systems across the Pacific Northwest. In this region, increasingly severe seasonality, characterized by wetter winters and drier summers, are expected to cause declines in prairie and pasture productivity. This is a significant problem to address because Northwest prairie and pasture systems currently sustain more than 1 million beef cows and cow-calf production costs are expected to increase to offset the effects of drought. The project will test the hypothesis that variation in plant species traits, caused by a decline in native species cover in favor of exotic grasses, will be reflected in the plant-fungi network's function. Network behaviors that regulate responses to drought will be measured to quantify interactions between plants and soil microbial communities that are complex, yet predictable. The project will assess plant and soil community sensitivity to experimentally imposed drought across a 520 kilometer latitudinal gradient. General hypotheses pertaining to the role of root-fungal networks in maintaining diverse prairie and low-diversity pasture productivity will be tested to address a major challenge for sustainability in the region and in similar systems elsewhere. Specifically, the proposed tasks will identify plant and fungal species that best maintain primary productivity, plant water-use efficiency, and foster carbon and nitrogen exchange in communities under stress. This knowledge will be used to determine thresholds of species composition and soil resource availability beyond which intervention is needed to prevent loss of biodiversity and resilience to drought. Alterations of mycorrhizal networks-mediated transfer or retention of carbon and nitrogen will be monitored using stable isotope labeling experiments to determine whether and how inter-specific connectivity increases community resilience and productivity under stress. A replicated nested design across a latitudinal gradient will be used to characterize network behaviors that can be simplified to improve inter-specific connectivity and resource transfer in native and managed systems. Passive and active resource transport among different plant species and fungi will be distinguished through stable isotope probing of DNA sequences and used to develop a spatially-explicit model for the scaling of mutualistic and competitive interactions affecting composition and function of common mycorrhizal networks.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.