Litter quality and stream food webs: a new paradigm for understanding interactions between microbes and invertebrates.

秋天落在溪流和河流中的树叶可以为生活在其中和周围的生物提供重要的食物资源。当树叶进入水中，细菌和真菌迅速殖民他们，并开始分解他们。叶子和微生物殖民者为生活在水中的昆虫幼虫提供食物，而昆虫幼虫反过来又为鱼类提供食物，最终在出现时，鸟类，蝙蝠和蜥蜴。这项研究将测试不同树木的叶子如何影响溪流和河流生态系统的食物网。研究人员将评估不同树种树叶的命运，以确定树叶是否主要被微生物分解剂转化为二氧化碳，或者树叶是否主要是昆虫幼虫的食物资源。科学家们认为，快速分解的叶子是昆虫更好的食物来源，这项研究挑战了这一假设，因为它们特殊的化学成分，分解较慢的叶子是昆虫更好的食物来源。该研究还将确定哪些微生物定殖特定的叶片类型，以及叶片类型沿着微生物定殖者如何影响食用它们的昆虫的营养质量。了解不同的树种如何影响生活在溪流中和溪流附近的动物，将指导管理人员种植最有益的树木。研究人员还将研究溪流的温度和水质如何影响昆虫利用树叶的方式。这可以帮助土地管理者了解某些河流条件是否使树叶成为昆虫更好的资源。 本研究项目将培训本科生和研究生，并与高中教师和学生合作。 研究结果将与致力于改善河流健康的政府和非政府组织分享。研究人员将使用多种最先进的技术来测试不同的树叶物种如何将能量和营养物质转移给微生物和昆虫。首先，研究人员将在绿色房子里种植12种不同的植物品种，使用13 C和15 N来标记将用于喂养昆虫的叶子。叶片衰老后，研究人员将收集叶片，并在亚利桑那州和新罕布什尔州的溪流中孵化，利用稳定的同位素特征来追踪叶片碳和氮向微生物和昆虫的转移。在溪流中吃树叶的昆虫将被带回实验室，在那里它们将被同位素比质谱仪分析，以准确测量有多少树叶碳和氮最终进入它们的组织。其次，研究人员将使用稳定同位素探测和DNA测序来研究哪些微生物是昆虫的良好食物来源，哪些微生物通过快速消耗储存在叶子中的碳和氮来与昆虫竞争。第三，科学家们将建造溪流中生态系统来控制温度和水质，以测试溪流条件如何影响树叶的营养质量。

Leaves that fall into streams and rivers in autumn can provide an important food resource for organisms that live in and around them. When leaves enter the water, bacteria and fungi rapidly colonize them and begin to decompose them. The leaves and microbial colonizers provide food for insect larvae that live in the water, which in turn, provide food for fish, and ultimately upon emergence, birds, bats and lizards. This study will test how leaves from different trees impact the food webs of stream and river ecosystems. The researchers will assess the fate of leaves from different tree species to determine whether the leaves are primarily converted into carbon dioxide by the microbial decomposers or whether the leaves are primarily a food resource for insect larvae. Scientists have assumed that leaves that decompose quickly are a better food source for insects and this research challenges that assumption by suggesting that leaves that decompose more slowly, because of their particular chemical composition, are a better food resource for insects. The research will also determine which microbes colonize specific leaf types and how leaf types along with their microbial colonizers affect the nutritional quality for insects that eat them. Understanding how different tree species affect the animals living in and near streams will guide managers to plant trees that are most beneficial. The researchers will also study how the temperature and water quality of streams affects how insects use leaves. This could help land managers understand if certain stream conditions make leaves a better resource for insects.  This research project will train undergraduate and graduate students and work with high school teachers and students. Results will be shared with the governmental and non-governmental organizations that are working to improve stream health.The researchers will use multiple state-of-the-art techniques to test how different leaf species transfer energy and nutrients to microbes and insects. First, investigators will grow twelve different plant species in the green house using 13C and 15N to label the leaves that will be feed to insects. After the leaf senescence, the researchers will collect the leaves and incubate them in streams in Arizona and New Hampshire, using the stable isotopic signatures to trace the transfer of leaf carbon and nitrogen to microbes and insects. Insects that eat the leaves in the stream will be brought back to the laboratory where they will be analyzed with an isotope ratio mass spectrometer to measure exactly how much of the leaf carbon and nitrogen ends up in their tissues. Second, the researchers will use stable isotope probing and DNA sequencing to study which microbes are a good food source for insects versus which microbes compete with insects by quickly using up the carbon and nitrogen stored in leaves. Third, scientists will construct stream mesocosms to control temperature and water quality to test how stream conditions affect the nutritional quality of leaves.