Collaborative Research: Headwater stream networks in a warming world: predicting heterotrophic ecosystem function using theory, multi-scale temperature manipulations and modeling

地球的河流系统接收、运输、储存和分解陆地生态系统产生的相当大比例的死亡植物材料。这种有机物分解的许多步骤很大程度上受到水温的影响，水温随着全球气温的上升而上升。虽然温度对其中一些步骤的影响在小范围内得到了较好的理解，但它们如何作为一个复杂的、综合的生态系统层面的过程相互作用，以在地球河流系统运行的大空间和时间尺度上推动温度上升的影响，仍然是一个悬而未决的问题。因此，需要进行研究，测试温度对整个生态系统中有机物分解的影响，明确目标是扩大这些结果，以了解整个河流和网络是如何处理有机物的。该项目将使用多个空间和时间尺度上的温度操纵数据来：1)提供生态学理论，利用基本原理来理解温度尺度如何从单个生物体到整个生态系统的影响；以及2)建立一个模型，模拟温度对整个森林溪流网络中有机质处理的影响。这项研究很重要，因为气温上升可能会以目前无法预测的方式改变溪流和河流的全球生物地球化学作用，使结果在未来的河流健康管理中有用。教育计划将是这一项目的组成部分，将包括开发公民科学项目，以及培训本科生、研究生和研究技术人员。该项目的野外工作将在美国北卡罗来纳州的考韦塔水文实验室进行，该实验室在河流生态系统中的有机物处理方面具有数十年的研究历史。第一个目标是了解气候变暖如何影响生物(真菌和无脊椎动物)，这些生物在河流中的有机物分解中起着至关重要的作用。该项目的这一部分将结合详细的基于实验室的真菌研究、在加热的河边水道中的实验以及对一条小森林溪流的整个范围的升温，以了解更高的温度如何改变真菌和动物分解者的群落结构。第二个目标是使用不同的温度控制来了解温度如何变化，以及溪流和河流中有机物处理的路径和速率。有机质的命运将通过实验室调查、河边水道和野外实验，结合有机质预算和食物网描述，在实验升温的溪流和匹配的参考溪流中进行研究。前两个目标的结果将与Coweeta站点现有的大量数据集相结合，以告知最终目标：建立一个生态模型，预测气候变暖对整个河流网络中有机物处理的影响。该模型还将纳入未来可能发生变化的其他重要因素，如降水和进入河流生态系统的有机物的相对质量。总而言之，这项研究将提供关于气候变暖如何影响溪流和河流的重要生物地球化学作用的亟需信息。

Earth's river systems receive, transport, store, and break down a substantial proportion of the dead plant material produced in terrestrial ecosystems. Many of the steps in the breakdown of this organic matter are greatly affected by water temperature, which is increasing along with air temperature globally. While the effects of temperature on some of these steps are understood relatively well at small scales, it remains an open question how they interact as a complex, integrated ecosystem-level process to drive the effects of rising temperatures at the large spatial and temporal scales over which Earth's river systems operate. Consequently, research is needed that tests the effects of temperature on organic matter breakdown in whole ecosystems, with the explicit goal of scaling up these results to understand how entire river reaches and networks process organic matter. This project will use data from temperature manipulations at multiple spatial and temporal scales to: 1) inform ecological theory that uses basic principles to understand how the effects of temperature scale from individual organisms to entire ecosystems; and 2) build a model that simulates the effects of temperature on organic matter processing in an entire forest stream network. This research is important because rising temperatures may alter the global biogeochemical role of streams and rivers in currently unpredictable ways, making the results useful in the future management of river health. An education program will be an integral part of this project and will include the development of a citizen science project, as well as training of undergraduates, graduate students and research technicians. Fieldwork for this project will take place at the Coweeta Hydrologic Laboratory, North Carolina, U.S.A., a site with a decades-long history of research on organic matter processing in stream ecosystems. The first objective is to understand how warming affects the organisms (fungi and invertebrates) that are critically important in organic matter breakdown in streams. This component of the project will combine detailed laboratory-based studies of fungi, experiments in heated streamside channels and the warming of an entire reach of a small forest stream to understand how higher temperatures change community structure of fungal and animal decomposers. The second objective is to use the various temperature manipulations to understand how temperature changes pathways and rates of organic matter processing in streams and rivers. The fates of organic matter will be studied using laboratory investigations, streamside channels, and field experiments combined with organic matter budgets and food web descriptions in the experimentally warmed stream and a matching reference stream. The results of these first two objectives will be combined with extensive existing datasets available at the Coweeta site to inform the final objective: construction of an ecological model that predicts the effects of warming on organic matter processing in an entire stream network. This model will also allow incorporation of other important factors that could potentially change in the future, such as precipitation and the relative quality of organic matter that enters stream ecosystems. Together, this research will provide much needed information about how warming influences the important biogeochemical role of streams and rivers.