Decomposition can be thought of as a continuous process beginning with fresh plant litter and leading to formation of increasingly refractory organic matter. This refractory material in turn influences nutrient availability, production, and carbon sequestration in ecosystems. At present, only early stages of the decomposition process have been intensively researched. The few long-term data available indicate the decomposition process begins with an initial rapid loss of labile litter constituents and becomes progressively slower as more recalcitrant compounds compose an increasingly large fraction of the remaining material. This continuum can be divided into two phases: the first phase is characterized by a relatively rapid loss of mass, immobilization of nutrients, and a rapidly declining overall decomposition rate; the second phase is characterized by uniformly slow decomposition rates and is accompanied by nutrient mineralization. Transition between these two phases appears to occur when the lignocellulose index reaches 0.5. A team of scientists, LIDET (Long-term Intersite Decomposition Experiment Team), has started a set of experiments to test whether these general relationships are consistent across a wide range of macroclimates and substrate qualities. These long-term experiments involve 17 LTER and 4 other cooperating sites, and a total of 31 types of litter. Experiments are designed to follow changes in mass, carbon fractions, and total nitrogen and phosphorus for up to 10 years. This newly funded component of the study supports the addition of 7 new sites to represent conditions that are not yet covered. It also supports the chemical characterization of changes in litter as it decomposes and testing of four decomposition models (CENTURY, GEM, GENDEC, and VEGIE) to predict long term dynamics across the full suite of 28 sites. The analysis and modeling exercise will assess the ability of models to predict the amount of carbon, nitrogen, and phosphorus during the second phase of litter decomposition, as well as the timing of transition between the initial phase of constant mass loss and the final phase of very slow mass loss. The LIDET team of twenty-eight scientists is coordinated through the electronic mail network established under LTER to foster intersite communication. This outstanding research team is coordinated by Drs.Harmon, Melillo, Moorhead, Parton, Rastetter and Aber.
