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

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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.