Detritus Inputs and Forest Soil Organic Matter Formation: Is There a Linear Relationship Between Detrital Input Rates and Soil Carbon Accumulation?.

Temperate forests presently remove the equivalent of up to ¼ of fossil fuel carbon emissions from the atmosphere and store much of this carbon in soil organic matter (SOM).  However, we lack a predictive understanding of how forest SOM pools respond to changes in aboveground detrital inputs and rhizodeposition that will accompany changes in net primary productivity associated with climate warming, precipitation shifts, and forest community composition.  Ecosystem models are often constructed assuming that increased detrital inputs associated with factors such as longer growing seasons, increased precipitation, warming-induced increases in nitrogen mineralization should contribute to larger accumulations of forest SOM and thus greater carbon storage in forest soils.  Likewise, models typically assume that environmental drivers functioning to decrease primary productivity and detrital inputs, such as drought, heat stress, and pathogens, should lead to decreases in forest SOM pool sizes and decreased carbon storage.  We present results from a network of long-term forest manipulation experiments- the DIRT (Detritus Input and Removal) Project, to test whether sustained increases and decreases in leaf litter inputs litter result in linear increases and decreases, respectively, in forest SOM pools when climatic and other variables are held constant at individual sites.  We also used root exclusion (with trenching), both alone and in combination with aboveground litter exclusion, to measure patterns of SOM change as related to belowground inputs.  Results of our DIRT studies and mechanistic studies conducted at DIRT sites and elsewhere will be used to evaluate whether carbon storage in forest SOM changes linearly with changes in above- and belowground plant inputs.