LTER Cross-site: Collaborative Research: DIRT: A Cross-continental, Experimental Study of Forest Soil Organic Matter and Nitrogen Dynamics

关于分解的大量研究都集中在有机物分解的短期、瞬时影响上。从这些研究中已经了解到许多关于凋落物养分含量和碳质在控制养分通过凋落物层循环到土壤有机质(SOM)中的作用。然而，关于植物凋落物的命运及其在决定土壤有机质含量和养分循环中的作用，人们所知的要少得多，时间尺度从几十年到几百年不等。为了解决这一差距，在三个美国和一个国际LTER地点的林地独立开展了控制土壤有机质形成或污垢(碎屑输入和清除处理)的长期实验研究。污地处理包括长期的地上和地下凋落物翻倍和清除。虽然这些装置的基本实验设计是相似的，但几乎没有共同的测量方法，每个地点的仪器都有很大的不同。这个LTER跨站点研究项目的目的是将这四个站点纳入统一的实验和测量范围，并通过这个网络测试各个站点所做的模型和假设。LTER项目是新兴的跨站点污垢网络的理想东道主，这既是因为它是许多研究人员的焦点，也是因为它专注于长期研究。土壤项目的中心目标是评估植物凋落物投入的比率和来源如何在十年时间尺度上控制森林土壤中有机质和养分的积累和动态。这种跨地比较将涉及三个具体目标：(1)研究森林地上部分生物量、有机质输入、来源和化学对净N保持和渗滤液中无机/有机N损失的影响；(2)研究森林地上部分化学对总N矿化、固定和硝化速率的影响；以及(3)评估碳源对土壤呼吸的模型的通用性。

0087006McDowellNumerous studies of decomposition have focused on short-term, transient effects of organic matter breakdown. Much has been learned from these studies about the roles of litter nutrient content and carbon quality in controlling the cycling of nutrients through the litter layer to soil organic matter (SOM). However, far less is known about the fate of plant litter and its role in determining SOM content and nutrient cycling over time scales ranging from decades to centuries. To address this gap, long-term experimental studies of controls on soil organic matter formation, or DIRT (Detritus Input and Removal Treatments), have been established independently at forested sites in three US LTERs and one international LTER site. DIRT plot treatments consist of long-term above- and below ground litter doubling and removal. While the fundamental experimental design of these installations is similar, there are few measurements in common and each site is instrumented quite differently. The purpose of this LTER cross-site research project is to bring these four sites into a general experimental and measurement uniformity, and to test models and hypotheses made at individual sites over this network. The LTER program serves as an ideal host for the emerging cross-site DIRT network both because it serves as a focal point for many investigators and because of its focus on long-term studies. The central goal of the DIRT project is to assess how rates and sources of plant litter inputs control accumulation and dynamics of organic matter and nutrients in forest soils over decadal time scales. This cross-site comparison will address three specific goals: (1) to examine effects of forest floor biomass, organic matter inputs, sources, and chemistry on net N retention and the ratio of inorganic to organic N losses in leachate; (2) to examine the effects of forest floor chemistry on gross N mineralization, immobilization, and nitrification rates; and (3) to evaluate the generality of models of sources of C to soil respiration.