Collaborative Research: Factors Regulating Below-Ground Carbon Allocation in Terrestrial Ecosystems: A Cross-Site Experimental Design

植物为小直径根及其相关菌根真菌的产生和维持投入了相当大的能量。这种地下碳分配如何响应氮等资源可用性的改变，是我们理解生态系统功能的基础。目前有两种相互竞争的理论：(1)氮有效性的增加减少了根的碳分配；(2)氮可用性的增加增加了根系的碳分配。了解细根的产生和死亡是这场冲突的核心。pi的总体假设是，根-菌根结合类型是控制根系碳分配、根系寿命和根系对氮有效性变化响应的主导因素。pi建议在代表一系列典型北美生态系统的四个长期研究地点，直接和独立地量化根产量和死亡率、菌根群落组成和丰度、根呼吸、土壤二氧化碳通量和地上凋落物。研究地点利用了外生菌根（EM）和丛枝菌根（AM）针叶树和硬木之间的对比，并代表了广泛的环境条件。试验添加N旨在解决C在一定规模上分配给根系的问题，这将解决关于生态系统水平上根系生长和周转如何响应氮有效性增加的争议。通过比较和对比不同气候和土壤条件下EM和AM主导的生态系统，我们将能够对控制细根周转的因素做出更普遍的陈述。

Ruess 9616537 Plants devote considerable energy to the production and maintenance of small-diameter roots and their associated mycorrhizal fungi. How this below-ground allocation of carbon responds to altered availability of resources such as nitrogen is fundamental to our understanding of ecosystem function. There are currently two competing theories: (1) increased N availability decreases C allocation to roots; and (2) increased N availability increases C allocation to roots. Understanding fine root production and mortality is at the heart of this conflict. The overall hypothesis of the PIs is that the type of root-mycorrhizal association is a dominant factor controlling carbon allocation to roots, root longevity and the response to root systems to changes in N availability. The PIs propose to directly and independently quantify root production and mortality, mycorrhizal community composition and abundance, root respiration, soil CO2 flux, and above-ground litterfall at four long-term study sites that represent a range of ecosystems typical of North America. The study sites capitalize on contrasts between ectomycorrhizal (EM) and arbuscular mycorrhizal (AM) conifers and hardwoods and represent a wide range of environmental conditions. Experimental additions of N are designed to address the issue of C allocation to roots at a scale that will resolve the controversy about how root growth and turnover at the ecosystem level responds to increasing N availability. By comparing and contrasting EM and AM dominated ecosystems under a variety of climatic and edaphic regimes, we will be able to make more universal statements about the factors controlling fine root turnover.