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

Pregitzer 9615509植物将相当大的能量用于生产和维护小直径的根及其相关的菌根真菌。这种地下碳分配如何应对氮等资源的可获得性变化，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)增加N的有效性会减少C向根的分配；(2)N的增加会增加C向根的分配。了解细根产量和死亡率是这场冲突的核心。PIs的总体假设是，根-菌根联合的类型是控制向根分配碳、根寿命和对根系对N有效性变化的反应的主导因素。PIs建议直接和独立地量化四个长期研究地点的根产量和死亡率、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，这些研究地点代表了北美典型的一系列生态系统。研究地点利用了外生菌根(EM)和丛枝菌根(AM)针叶和硬木之间的对比，并代表了广泛的环境条件。N的试验性添加旨在解决C向根的分配问题，这将解决关于生态系统水平上的根生长和周转如何对N有效性增加做出反应的争议。通过对不同气候和土壤条件下EM和AM主导的生态系统的比较和对比，我们将能够对控制细根周转的因素做出更普遍的陈述。

Pregitzer 9615509 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.