LTREB renewal: Progressive Responses to Environmental Change Across Multiple Ecosystems

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This project investigates how four different ecosystems in the southwestern U.S. respond to changes in temperature and precipitation. This is important because temperature and precipitation have strong effects on ecosystems. The main effects are on the flow of carbon, the supply of nutrients, the types of soil microbes, and the growth of plants. However, the exact rate and magnitude of change are unknown. This project will investigate a key knowledge gap by using experimental treatments that reduce precipitation and warm soil. This experiment has been sustained for almost two decades. This project will support the completion of the experiment in the next five years. The main question is whether the initial responses to shifts in temperature and precipitation are consistent over time, or whether the ecosystems adjust to the new conditions. In addition, this project will support scientific workforce training. Undergraduate and graduate students will be trained in methods of data collection and analysis. Outreach activities will be conducted with broad audiences through local non-profit groups. Finally, data will be provided online about primary production, plant community composition, and ecosystem carbon and nutrient balance, in open access format.This project will extend a unique long-term experiment conducted across multiple ecosystem types, extending the timeline to over two decades. This experiment occurs along the C. Hart Merriam elevation gradient, extending from the forested slopes of the San Francisco Peaks to the woodlands and deserts of the Colorado Plateau, a region identified for its high sensitivity to climate. The project follows up on an earlier hypothesis that change in temperature and precipitation will elicit progressive reductions in primary production in semi-arid ecosystems that are sustained on decadal timescales. In other words, primary production may increasingly decline in response to the interactive effects of drought and heat. Here, two mechanisms will be tested that could drive this change: shifts in the plant community and changes in the nitrogen cycle. The prediction is that the combination of these two effects modulates long-term carbon and nutrient balance responses to experimental warming. Because these progressive effects operate on the timescales of community change and biogeochemistry (years to decades), measuring them requires continuing this long-term dataset. In this case, two decades will be sufficient time to see experimental responses of total ecosystem carbon and nitrogen balance. It is likely that that these responses will vary among the biomes represented along the elevational gradient, with the variation largely explained by the magnitude of the progressive effects. Testing these progressive effects across ecosystems ranging from desert grasslands to coniferous forests will fill critical knowledge gaps in ecosystem science.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.