Ecosystem engineers in the subarctic

生物的生长和分布主要由非生物条件决定。然而，一些生物体改变了它们的环境，使生长、分配和生态系统过程与场地条件分离。除了我们对营养相互作用如何影响群落和生态系统的传统理解外，生态系统工程的概念还提供了一套机制，使某些物种可以改变栖息地和资源的可用性。我的工作将是独一无二的，研究了亚北极碎屑和消费者食物链中两个对立的生态系统工程过程。首先，我将确定植物及其菌根在多大程度上改造了林线附近的低生产力土壤，抑制了许多植物物种在这些栖息地生存的能力，并减少了消费者食物链的食物供应。其次，我将研究食肉动物如何通过粪便和尿液沉积来破坏这些栖息地。因此，它们将对消费者食物链产生积极的反馈，在冻土带和林地上创造独特的植物群落，并增加冻土带上树岛的生长和存活。最近的研究表明，一些菌根协会允许植物从土壤有机质中获得养分。在亚北极高地栖息地占主导地位的芥科植物，其菌根真菌可能在分解有机物方面特别有效，因为它们保留了腐生祖先的纤维素降解酶。通过获取有机质中的养分，这些真菌可能会通过减少土壤养分的有效性来减缓分解。我将确定这种营养循环的短路是否发生在亚北极地区，这将解释这些系统中土壤有机质的大量积累，以及依赖传统无机营养来源的植物的缺乏。我将使用稳定同位素分析来测量有机元素的摄取。利用根部和真菌排除法进行的施肥实验，以及监测野火过后的土壤发育，将使我们能够发现控制土壤养分循环和碳保持的机制。我还将在我之前关于狐狸放牧活动如何创造补丁营养丰富的工作的基础上，使独特的植物群落能够在通常营养不良的生境中建立起来。食肉动物土壤肥沃的概念将扩展到研究亚北极冻土带上的树线和树岛上的树木，在那里，大型食肉动物(狼和鹰)优先使用某些树岛作为避难所和栖息地。然后，植物生产力的变化将与食草动物种群动态联系在一起。考虑到在亚北极和那里发现的大型土壤有机质池中气候变化的快速发生，这些研究将为学生提供基本的培训，使他们成为在这些脆弱的系统中工作的研究人员和自然资源管理者，并为他们提供预测和管理自己命运的工具。

The growth and distribution of organisms are primarily determined by abiotic conditions. However, some organisms modify their environment, uncoupling growth, distribution and ecosystem processes from site conditions. In addition to our traditional understanding of how trophic interactions affect communities and ecosystems, the concept of ecosystem engineering offers a set of mechanisms whereby some species modify habitats and resource availability. My work will be unique, examining two opposing ecosystem engineering processes in the detrital and consumer food chains in the subarctic. First, I will determine the degree to which plants and their mycorrhizae engineer low productivity soils near the tree line, inhibiting the ability of many plant species to exist in these habitats and reducing food availability for the consumer food chain. Second, I will examine how carnivores disrupt these habitats via fecal and urine deposition. They will therefore have a positive feedback on the consumer food chain, creating unique plant communities on the tundra and woodlands, and increase the growth and survival of tree islands on the tundra. Recent research shows that some mycorrhizal associations allow plants access to nutrients from soil organic matter. Ericaceous plants, which dominate upland subarctic habitats, have mycorrhizal fungi that may be particularly effective at breaking down organic matter since they retain the cellulose-degrading enzymes of their saprophytic ancestors. By accessing nutrients in organic matter, these fungi may slow decomposition by reducing soil nutrient availability. I will determine if this short-circuiting of the nutrient cycling occurs in the subarctic, which would explain the massive buildup of soil organic matter in these systems and the absence of plants that rely on conventional inorganic sources of nutrients. I will use stable isotope analysis to measure organic element uptake. Fertilization experiments using root and fungal exclusion, and monitoring soil development after wildfires, will allow us to discover the mechanisms controlling soil nutrient cycling and carbon retention. I will also build on my previous work on how fox denning activity creates patches of nutrient enrichment, allowing unique plant communities to establish in what would typically be nutrient-poor habitat. The concept of soil enrichment by carnivores will be extended to studying trees at the treeline and tree islands on the subarctic tundra where large carnivores (wolves and eagles) preferentially use certain tree islands for shelter and perching. Modification of plant productivity will then be linked to herbivore population dynamics. Given the rapid rate of climate change occurring in the subarctic and large pools of soil organic matter found there, these studies will provide essential training to students becoming researchers and natural resources managers working in these fragile systems, and give them tools to predict and manage their fate.