LTER: The Role of Biogeochemical and Community Openness in Governing Ecological Change in Arctic Ecosystems

北极是地球上变暖最快的地区之一，因此可以很好地提供未来可能发生在更南方的变化的想法。这种变暖增加了阿拉斯加北部生态系统中野火和永久冻土融化等干扰。由于气候变暖和干扰增加，陆地、溪流和湖泊中的动植物群落正在发生变化。这些群落变化的基础是养分的可得性和循环、土壤和植被中储存的碳量以及北极景观与大气、下游河流和海洋之间二氧化碳和养分交换的变化。总的来说，这些变化可能会产生深远的影响，不仅对北极生态系统，而且对全球，对人类也有影响。更好地了解这些变化可以更好地预测未来，而这些预测可以为更好的规划提供基础。为了了解这些变化，北极长期生态研究（ARC-LTER）项目的科学家们监测了阿拉斯加图里克湖附近陆地、河流和湖泊生态系统的长期变化。他们观察这些生态系统从自然和实验施加的干扰中恢复的情况，并发起和维持长期实验，旨在了解北极物种之间的相互作用、营养循环以及北极景观中陆地和水生生态系统之间的联系。在ARC-LTER站点工作的科学家将吸引来自阿拉斯加巴罗的学生，为记者开展一个项目，并参加在三个社区为阿拉斯加原住民举办的短期课程，所有这些都旨在增加公众对北极生态的了解。向国家和州的土地管理者和资源管理者提供简报将有助于提供可以为政策提供信息的科学知识。研究围绕生态系统开放性和景观连通性的概念进行。生物地球化学开放性是指生态系统对外部营养物质和有机碳来源的依赖程度，而不是生态系统内部循环的营养物质和光合作用在当地产生的有机碳。群落开放性是指生物在生态系统内外的运动决定群落和食物网结构的程度。最后，景观连通性描述了景观中生态系统之间相互作用的性质和强度，以及由此产生的对景观中干扰的响应的传播。北极景观的组成部分在生物地球化学和社区开放方面差异很大。ARC-LTER的研究将比较北极的主要生态系统，以确定它们的开放程度如何控制它们对气候变化和急性干扰（如火灾和与永久冻土融化相关的地表滑坡）的反应。拟议的研究还将确定景观连通性以及北极景观中营养物质、碳和生物的运动如何调节对气候和干扰的响应。为了实现这些目标，ARC-LTER研究将包括持续的长期肥料和增温试验；监测化学收支、群落变化和物种运动；监测以前施肥过的苔原、河流和湖泊的恢复情况；在不同的古老景观中建立新的更大的温室；阻止鱼类进入与洄游溪流相连的湖泊，并将鱼类添加到目前与河流网络隔离的湖泊；寻找陆地产量与水生代谢和营养浓度之间的相关性。这项研究每年将支持两名本科生研究人员，并为从事其他项目的学生提供在北极LTER站点和实验工作的机会。

The Arctic is one of the fastest warming regions on Earth and as such may well provide an idea of the future changes likely to occur further south. This warming has increased disturbances such as wildfire as well as thawing of permafrost in ecosystems of Northern Alaska. As a result of this warming and increased disturbance, animal and plant communities on land and in streams and lakes are changing. Underlying these community changes are changes in the availability and cycling of nutrients, in the amount of carbon stored in soils and vegetation, and in the exchange of carbon dioxide and nutrients between arctic landscapes and the atmosphere and downstream rivers and oceans. Collectively, these changes may have profound effects, not just on the arctic ecosystems, but globally, with implications for humans. A better understanding of these changes can lead to better predictions of the future, and those predictions could provide the basis for better planning. To understand these changes, scientists with the Arctic Long-Term Ecological Research (ARC-LTER) Project monitor long-term changes in terrestrial, stream, and lake ecosystems in the vicinity of Toolik Lake, Alaska. They make observations of the recovery of these ecosystems from natural and experimentally imposed disturbances, and initiate and maintain long-term experiments designed to understand interactions among arctic species, nutrient cycles, and the connections among terrestrial and aquatic ecosystems on the arctic landscape. Scientists working at the ARC-LTER site will engage students from Barrow, Alaska, run a program for journalists, and participate in short courses for Alaskan Natives in three communities, all designed to increase the public understanding of Arctic Ecology. Briefings to national and state land managers and resource managers will help provide scientific knowledge that can inform policy.The research is organized around the concepts of ecosystem openness and landscape connectivity. Biogeochemical openness is the degree to which ecosystems depend on external sources of nutrients and organic carbon versus nutrients recycled within the ecosystem and organic carbon produced locally by photosynthesis. Community openness is the degree to which the movement of organisms in and out of the ecosystem determines community and food-web structure. Finally, landscape connectivity describes the nature and strength of interactions among ecosystems on the landscape and the resultant propagation of responses to disturbances across the landscape. Components of the arctic landscape differ widely in biogeochemical and community openness. Research at the ARC-LTER will compare key ecosystems of the Arctic to determine how their degree of openness governs their responses to climate variation and to acute disturbance such as fire and surface slumping associated with permafrost thaw. The proposed research will also determine how the responses to climate and disturbance are mediated by landscape connectivity and the movement of nutrients, carbon, and organisms across arctic landscapes. To accomplish these goals, ARC-LTER research will include continued long-term fertilizer and warming experiments; monitoring of chemical budgets, community changes, and species movements; monitoring recovery of tundra, rivers, and lakes that were previously fertilized; establishing new larger greenhouses in different aged landscapes; blocking fish movement into a lake connected to migratory streams and adding fish to a lake currently isolated from a stream network; and searching for correlations between terrestrial production and aquatic metabolism and nutrient concentrations. This research will support two undergraduate student researchers per year and provide opportunities for students working on other projects to work on Arctic LTER sites and experiments.