LTREB renewal: Progressive Responses to Environmental Change Across Multiple Ecosystems

这个项目调查了美国西南部四种不同的生态系统如何对温度和降水的变化做出反应。这一点很重要，因为温度和降水对生态系统有很强的影响。主要影响是碳的流动、养分的供应、土壤微生物的种类和植物的生长。然而，确切的变化速度和幅度是未知的。该项目将通过使用减少降水和温暖土壤的试验性处理来调查一个关键的知识缺口。这个实验已经持续了将近二十年。该项目将在未来五年内支持实验的完成。主要的问题是，对温度和降水变化的最初反应是否随着时间的推移而保持一致，或者生态系统是否会适应新的条件。此外，本项目将支持科学劳动力培训。本科生和研究生将接受数据收集和分析方法方面的培训。将通过当地非营利组织与广大受众开展外联活动。最后，将以开放获取格式在线提供有关初级生产、植物群落组成和生态系统碳和营养平衡的数据。该项目将扩展一个独特的长期实验，在多个生态系统类型中进行，将时间延长到20多年。这个实验沿着C. Hart Merriam海拔梯度进行，从旧金山山峰的森林斜坡延伸到科罗拉多高原的林地和沙漠，该地区对气候高度敏感。该项目是对先前的一个假设的后续，即温度和降水的变化将导致半干旱生态系统初级生产的逐步减少，这种减少在十年时间尺度上是持续的。换句话说，由于干旱和高温的相互作用，初级生产可能会日益下降。在这里，将测试两种机制来驱动这种变化：植物群落的变化和氮循环的变化。我们的预测是，这两种效应的结合调节了碳和养分平衡对实验变暖的长期响应。由于这些渐进式效应在群落变化和生物地球化学的时间尺度上（几年到几十年）起作用，测量它们需要持续这个长期的数据集。在这种情况下，20年的时间将足以观察生态系统总碳氮平衡的实验响应。这些响应很可能在不同海拔梯度的生物群系中有所不同，这种变化在很大程度上可以用递进效应的大小来解释。在从沙漠草原到针叶林的生态系统中测试这些渐进效应将填补生态系统科学的关键知识空白。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.