Biogeochemical Responses to Variations in Climate and Disturbance in Terrestrial Ecosystems

与农业生态系统几乎完全依赖于通过施肥提供的外部养分不同，大多数自然的陆地生态系统，如森林、草原和苔原，几乎完全依赖于内部循环的养分来支持植物生长。在这些自然生态系统中，来自风化基岩和雨水和灰尘沉积的氮和磷等营养物质的供应非常缓慢，以至于这些外部来源只能满足不到5%的年植物生产力。相反，这些生态系统在数千年的时间里积累养分，并通过内部营养循环重新利用和回收它们。这种对内部循环养分的几乎完全依赖意味着，这些生态系统对不断变化的环境或干扰的反应必须依赖于生态系统中已有养分的再分配，至少在最初的几十年里是这样。数百年来，这些反应取决于生态系统保留和回收更多营养物质的能力。该项目将比较和对比不同类型的生态系统，从草原到森林，从热带到北极，并开发一个通用模型来描述这些生态系统如何随着时间的推移积累养分，以及它们对循环养分的依赖如何影响它们对气候变化、二氧化碳升高以及野火、生物质收获或风暴破坏等干扰的反应。这项研究有望对我们对一般生态系统功能的理解做出重要贡献，这将有价值地增加对世界各地生态系统如何被调节，它们如何应对气候和干扰，以及它们如何在未来作为二氧化碳汇进行管理的理解。它还将增加对生态系统在稳定性和对干扰的恢复能力方面如何以及为何不同的理解。研究人员还将开发一个用于本科课程的教学模块，让学生探索生态系统的营养调节。该模型和相关数据将在网络上提供给研究人员和教育工作者，也将用于连接海洋生物实验室的研究和教育项目。本项目将支持1名全职博士后学者和1名硕士级研究助理。该项目建立在多元素限制模型中阐述的生态系统内资源优化和元素相互作用理论的基础上，该模型模拟了植被和土壤微生物获取资源的优化，生态系统内营养循环的同步，以及这些营养循环与生态系统中能量、碳和水通量的耦合。通过对现有数据的综合和陆地生态系统中碳、氮、磷和水之间相互作用模型的实施和分析，该项目将研究生物地球化学对气候和扰动响应的限制，以及对碳固存和生态系统营养资本的影响。资源优化描述了植物和微生物如何调节重要资源的获取，以维持其代谢平衡和最大化生长。正是通过这种优化和植物与土壤微生物之间的平衡相互作用，生态系统才能积累重要的营养物质并在内部循环利用，从而实现更高的产量和碳固存。通过比较和对比几种不同类型陆地生态系统对气候和干扰恢复的响应，本项目将进一步推进生态系统中资源优化和元素相互作用理论，评估生态系统内紧密的营养循环同步机制，并评估全球碳和营养封存或损失的潜力。

Unlike agricultural ecosystems that rely almost exclusively on an external supply of nutrients through fertilizer application, most natural, land-based ecosystems, like forests, prairies, and tundra, rely almost exclusively on internally recycled nutrients to support plant growth. In these natural ecosystems, the supplies of nutrients like nitrogen and phosphorus from weathering bedrock and deposition in rain and dust are so slow that less than 5% of the annual plant productivity can be met from these external sources. Instead, these ecosystems accumulate nutrients over thousands of years and reuse and recycle them via internal nutrient cycles. This almost exclusive dependence on internally recycled nutrients means that the response of these ecosystems to a changing environment or to disturbance has to rely on a redistribution of nutrients already in the ecosystem, at least for the first few decades. Over hundreds of years, these responses depend on the ability of the ecosystem to retain and recycle more nutrients. This project will compare and contrast various types of ecosystems, from grassland to forest, from tropical to arctic, and develop a general model to describe how these ecosystems accumulate nutrients over time and how their dependence on recycled nutrients affects their responses to a varying climate, elevated carbon dioxide, and disturbances like wildfire, biomass harvest, or storm damage. The study promises to make an important contribution to our understanding of general ecosystem function, which will be valuable to increase understanding of how ecosystems around the world are regulated, how they respond to climate and disturbance, and how they can be managed as a sink for carbon dioxide in the future. It will also increase understanding of how and why ecosystems differ in their stability, resilience to disturbance. Researchers also will develop a teaching module for use in undergraduate courses to allow students to explore nutrient regulation of ecosystems. The model and associated data will be available to researchers and educators on the web and will also serve to link both research and educational programs at the Marine Biological Laboratory. This project will support one full-time post-doctoral scholar and a masters-level research assistant. This project builds on a theory of resource optimization and element interactions within ecosystems as formulated in the Multiple Element Limitation model, which simulates the optimization of resource acquisition by vegetation and soil microbes, the synchronization of nutrient cycles within ecosystems, and the coupling of these nutrient cycles with energy, carbon, and water fluxes through ecosystems. Through synthesis of existing data and the implementation and analysis of a model of the interactions among carbon, nitrogen, phosphorus, and water in terrestrial ecosystems, this project will examine biogeochemical constraints on responses to climate and disturbance and the consequent effects on carbon sequestration and ecosystem nutrient capital. Resource optimization describes how plants and microbes regulate the acquisition of vital resources to both maintain their metabolic balance and maximize growth. It is through this optimization and the balanced interactions between plants and soil microbes that ecosystems can accumulate vital nutrients and recycle them internally, which in turn allows higher production and carbon sequestration than would otherwise be possible. By comparing and contrasting responses to climate and recovery from disturbance in several different types of terrestrial ecosystem, this project will further advance the theory of resource optimization and element interactions in ecosystems, assess the mechanisms by which tight within-ecosystem nutrient cycles are synchronized, and evaluate the potentials of carbon and nutrient sequestration or loss across the globe.