Ecosystem engineers in the subarctic

生物的生长和分布主要是由非生物条件决定的。然而，一些生物改变它们的环境，使生长、分布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之外，生态系统工程的概念还提供了一些物种改变栖息地和资源可用性的机制。我的工作将是独特的，研究两个相反的生态系统工程过程在碎屑和消费食物链在亚北极。首先，我将确定植物及其菌根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，并促进冻土带上树岛的生长和生存。最近的研究表明，一些菌根关联允许植物从土壤有机质中获取营养。占据亚北极高地栖息地的Ericaceous plants有菌根真菌，它们在分解有机物方面可能特别有效，因为它们保留了腐生植物祖先的纤维素降解酶。通过获取有机物中的养分，这些真菌可能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，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失。我将使用稳定同位素分析来测量有机元素的吸收。利用根和真菌隔离的施肥试验，以及监测野火后土壤的发育，将使我们能够发现控制土壤养分循环和碳保持的机制。我还将在我之前的工作基础上，研究狐狸的筑巢活动如何创造营养丰富的斑块，使独特的植物群落在通常营养贫乏的栖息地建立起来。食肉动物丰富土壤的概念将扩展到研究亚北极苔原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住所和栖息。植物生产力的改变将与食草动物种群动态联系起来。考虑到亚北极地区气候变化的速度之快，以及在那里发现的大量土壤有机质，这些研究将为成为在这些脆弱系统中工作的研究人员和自然资源管理者的学生提供必要的培训，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.