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，有些生物改变了它们的环境，使生长、分布和生态系统过程与场地条件脱钩。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，使某些物种能够改变栖息地和资源可用性。我的工作将是独特的，研究两个对立的生态系统工程过程中的碎屑和消费者的食物链在亚北极。首先，我将确定植物和它们的真菌在多大程度上改造了林木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中生存的能力，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生存。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。杜鹃花科植物，占主导地位的高地亚北极栖息地，有菌根真菌，可能是特别有效的分解有机物，因为他们保留了纤维素降解酶的saceritic祖先。通过获取有机物质中的营养物质，这些真菌可能会通过减少土壤养分的可用性来减缓分解。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缺乏依赖传统无机营养源的植物。我将使用稳定同位素分析来测量有机元素的吸收。利用根系和真菌排除的施肥实验，以及野火后监测土壤发育，将使我们能够发现控制土壤养分循环和碳保持的机制。我还将建立在我以前的工作上，关于狐狸筑巢活动如何创造营养富集的补丁，允许独特的植物群落在通常营养贫乏的栖息地建立。食肉动物的土壤富集的概念将扩展到研究树木的树线和树岛的亚北极苔原，大型食肉动物（狼和鹰）优先使用某些树岛的住房和栖息。植物生产力的改变将与食草动物种群动态联系起来。鉴于亚北极地区气候变化的速度很快，而且在那里发现了大量的土壤有机物，这些研究将为学生提供必要的培训，使他们成为在这些脆弱系统中工作的研究人员和自然资源管理人员，并为他们提供预测和管理其命运的工具。

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.