Dimensions: Taxonomic, genetic and functional biodiversity of above-ground bacterial endophytes in subalpine conifers

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Nitrogen (N) is essential to all life on Earth, but only select microbes can reduce or 'fix' N to a form that plants can use. Typically, plants can only use atmospheric N can when fixed by microbes that live in the soil or via a symbiotic relationship with legumes, but recent findings indicate that bacteria inside pine needles can also perform this critical function. In this research, investigators at University of California, Merced will examine the symbiosis between bacteria and limber pine (Pinus flexilis). The goals are to understand the diversity of bacteria present in pine needles, calculate how much N microbes fix and under what conditions, and infer how this fixed N is transferred to the tree. The research could significantly improve our understanding of the N cycle and help identify a currently unknown source of fixed N within coniferous forests. A more complete understanding of the N cycle will also help improve climate models, and a better characterization of the microbes that can fix Nitrogen could lead to advances in crop development. This research will train undergraduates. graduate students and post-doctoral researchers in both field and lab techniques. Additionally, the research will include outreach to teachers, administrators and students at a K-8 STEM school serving under-represented groups, and will develop inquiry-based learning modules in line with Common Core educational standards for incorporation within the K-8 STEM curriculum.The investigators will examine how the phylogenetic diversity and genetic potential of subalpine tree endophytes affect N fixation within western coniferous forests. Their central hypothesis is that across its broad geographic range, limber pine hosts a broad taxonomic, genetic and functional biodiversity of mutualistic N fixing endophytes, shaped by the local environment, and shared, in part, with neighboring trees. To test this, investigators will examine the biodiversity of endophytes in limber pine and co-occurring species across the limber pine range, identify the factors that structure the patterns of diversity, and determine the relationship between taxonomic diversity and N fixation. Cutting-edge methods in sequencing and genome analysis will be integrated with established and highly sensitive methods for detecting and visualizing N fixing activity in situ to understand how endophyte diversity is shaped by the environment and shapes the N cycle in subalpine forests.