Autumnal Litter Input in DIRT Litter Manipulation Experiment at Harvard Forest 2008

Climate change will alter forest ecosystem productivity, changing the quantity and quality of detrital inputs to soil and altering rates of soil organic matter (SOM) accumulation and stabilization. To examine changes in forest soil SOM pools, we have used the Detritus Input and Removal Treatments (DIRT) Project to alter organic matter input rates and sources (roots, leaves) to soils, allowing us to measure contributions of organic matter sources to long-term SOM storage at five temperate forests (Harvard Forest, HJ Andrews, Bousson (PA) Experimental Forest (BEF), U. Michigan Biological Station (UMBS), Síkfokut ILTER, Hungary). Organic matter inputs are altered by excluding or adding leaf inputs, or by excluding roots from forested plots. Soil respiration partitioning at HF, BEF, and UMBS shows that soil fertility controls the allocation of C to above- and belowground tissue. At UMBS, glacial outwash sandy soils are extremely low in N, and C released from root respiration plus root litter decomposition is 87% of total soil respiration. Conversely, at the N-rich BEF site, total belowground sources of CO2 are only 61% of soil respiration, with 47% attributed to root litter. These data suggest that at BEF, leaf litter, comprising only 39% of soil respiration, would be a more important source of long-term SOM than root litter. However, soil chemistry and radiocarbon data have shown us that long-term soil C storage is complex. The year 2010 represents the 20-year anniversary of the initiation of DIRT treatments at the Harvard Forest (2010), and we are therefore planning to conduct systematic sampling campaigns for a comprehensive study of changes in SOM quality after long-term manipulation of inputs. One objective is to quantify how 20 years of litter input alterations have affected SOM quantity and quality at the surface (0-20 cm) and deeper in the soil profile (20-100 cm). To uderstand these changes, we need to quantify the quantity and quality of aboveground litter inputs. Total aboveground litter inputs were 300.4 + 8.9 (SE, n=21) g m-2. In congruence with the data for aboveground biomass, black oak contributed the dominant mass (73.9%) of litter inputs; red maple and paper birch together contributed 23.26% of the total. Six other tree species collectively constituted the balance of litter inputs.