The Detrital Input and Removal Treatment (DIRT) Project was established to assess how rates and sources of plant litter inputs influence accumulations or losses of organic matter in forest soils. DIRT employs chronic additions and exclusions of aboveground litter inputs and exclusion of root ingrowth to permanent plots at eight forested and two shrub/grass sites in the northern hemisphere to investigate how soil organic matter (SOM) dynamics are influenced by plant detrital inputs across ecosystem and soil types. The long-term DIRT study at the H.J. Andrews Experimental Forest was established in an old-growth forest stand on the valley floor and aims to address how detrital quality and quantity control soil organic matter accumulation and stabilization. The DIRT plots consist of treatments that double leaf litter, double woody debris inputs, exclude aboveground litter inputs, remove root inputs via trenching, or remove all organic matter inputs. We measured changes in soil solution chemistry with depth, and conducted long-term incubations of bulk soils from different treatments in order to elucidate effects of detrital inputs on the relative amounts and lability of different soil C pools. These data include various properties of the DIRT plots obtained during re-measurements at various intervals. C and N concentrations and content in soil, CO2 efflux, and soil solution chemistry are measured from bulk samples to 1 m depth, field respiration measurements, and lysimeters at 2 depths, respectively, and assessed at Oregon State University.
April Strid, Derek Pierson, Fox Sparky Peterson, Hayley Peter-Contesse, Jennifer Dawn Wig, Kate Lajtha, Kim Townsend, Phillip Sollins
Soil organic matter (SOM) is the terrestrial biosphere's largest pool of organic carbon and is an integral part of the global C cycle. Therefore, changes in SOM formation and decomposition due to climate change, land management, disturbance or other factors can feed back to the climate system to either sequester CO2 into organic forms or release it to the atmosphere. Despite its pivotal role in the global C cycle, the relative importance and linkages of the various biological, chemical and physical processes regulating SOM balances are not well understood. Although forests contain more than 3x the soil C (575 x 1015 g) of agricultural lands (180 x 1015 g), forest SOM dynamics and their relation to detrital inputs and soil biotic processing remain poorly understood. Even fundamental relationships, such as between mean annual temperature and SOM turnover rates, are controversial. A major challenge for environmental science is to develop a predictive understanding of how climate and vegetation interact to determine how detritus and soil biota affect SOM formation and stability. Over the years, our informal group of ecologists, biogeochemists and ecosystem modelers has been using a common set of experimental manipulations, referred to collectively as DIRT (Detritus Input and Removal Treatments), to assess how rates and sources of plant inputs control the accumulation and dynamics of SOM and nutrients in forest soils over decadal time scales. The original DIRT treatments consist of chronically altering plant inputs to forest soils by regularly removing surface litter from permanent plots and adding it to others. Our network of DIRT sites now includes four operational temperate forest sites. The central goal of the DIRT project is to assess how rates and sources of plant litter inputs control the accumulation and dynamics of organic matter and nutrients in forest soils over decadal time scales. The project examines processes at multiple levels, across decades and centuries, exploring the intricate interconnections of biology and chemistry that lead to the formation of humic materials over these hitherto unexplored long time spans. Our plots are part of an informal network of similar experimental treatments that span a significant climatic gradient and that encompass both coniferous and deciduous forests, and that vary widely in anthropogenic N loading. Current DIRT sites include Harvard Forest, MA (oak forest, established 1991); Bousson Experimental Research Reserve, PA (deciduous forest, established 1992); Sikfokut Forest, Hungary (turkey oak forest, established 2001), and the Michigan Biological Station, MI (pine forest, established 2004).