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及灰尘沉积的氮和磷等营养物质的供应非常缓慢，这些外部来源只能满足植物年生产力的不到5%。相反，这些生态系统积累了数千年的营养物质，并通过内部营养循环对其进行再利用和再循环。这种几乎完全依赖于内部再循环的养分意味着这些生态系统对环境变化或干扰的反应必须依赖于生态系统中已有养分的重新分配，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各种类型的生态系统，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，以及它们对回收养分的依赖如何影响它们对变化的气候，二氧化碳浓度升高以及野火，生物质收获或风暴破坏等干扰的反应。这项研究有望为我们理解一般生态系统功能做出重要贡献，这将有助于加深对世界各地生态系统如何调节，它们如何应对气候和干扰以及如何管理它们作为未来二氧化碳的汇的理解。它还将增加对生态系统在稳定性和对干扰的恢复力方面如何以及为什么不同的理解。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控。该模型和相关数据将在网上提供给研究人员和教育工作者，并将有助于将海洋生物实验室的研究和教育方案联系起来。该项目将支持一名全职博士后学者和一名硕士级研究助理。该项目建立在多元素限制模型中制定的生态系统内资源优化和元素相互作用的理论基础上，该模型模拟了植被和土壤微生物对资源获取的优化，生态系统内养分循环的同步，以及这些养分循环与生态系统中能量，碳和水通量的耦合。通过综合现有数据，实施和分析陆地生态系统中碳、氮、磷和水之间相互作用的模型，本项目将研究生物地球化学对气候和干扰反应的制约，以及对碳固存和生态系统养分资本的影响。资源优化描述了植物和微生物如何调节重要资源的获取，以保持其代谢平衡并最大限度地增长。正是通过这种优化以及植物和土壤微生物之间的平衡相互作用，生态系统可以积累重要的营养物质并在内部进行循环，从而实现比其他方式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的响应和从干扰中恢复，该项目将进一步推进生态系统中资源优化和元素相互作用的理论，评估生态系统内紧密的养分循环同步的机制，并评估整个地球仪的碳和养分固存或损失的潜力。

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.