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

许多关于分解的研究都集中在有机物分解的短期、瞬时效应上。从这些研究中，我们了解到凋落物养分含量和碳质量在控制养分通过凋落物层向土壤有机质（SOM）循环中的作用。然而，人们对植物凋落物的命运及其在确定SOM含量和养分循环中的作用知之甚少，时间尺度从几十年到几个世纪不等。为了弥补这一差距，在三个美国LTER和一个国际LTER站点的森林站点独立建立了控制土壤有机质形成的长期实验研究，或DIRT（碎屑输入和去除处理）。DIRT地块处理包括长期的地上和地下凋落物加倍和清除。虽然这些装置的基本实验设计是相似的，但有一些共同的测量，每个站点的仪器都有很大的不同。这一LTER跨站点研究项目的目的是使这四个站点具有普遍的实验和测量一致性，并通过这一网络测试各个站点的模型和假设。LTER计划是新兴的跨站点DIRT网络的理想宿主，因为它是许多研究者的焦点，也因为它专注于长期研究。DIRT项目的中心目标是评估植物凋落物输入的速率和来源如何在十年时间尺度上控制森林土壤中有机物质和养分的积累和动态。这种跨站点的比较将解决三个具体目标：（1）检查森林地面生物量，有机质输入，来源和化学对净N保留和渗滤液中无机与有机N损失的比例的影响：（2）检查森林地面化学对总N矿化，固定和硝化速率的影响。（3）评价土壤呼吸碳源模型的通用性。

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.