The exact mechanism(s) controlling belowground responses to elevated N deposition in northern hardwood forest ecosystems are unknown; however, recent studies have suggested that suppressed soil respiration and elevated DOC export might be associated with changes in the decomposition of litter in the forest floor. To address the separate and combined effects of litter biochemistry, microbial decomposer community, and N availability in controlling these processes, we conducted a reciprocal litterbag transplant study using partially decomposed forest floor litter and freshly fallen leaf litter from two previously studied Great Lakes Sugar Maple-dominated northern hardwood forest stands receiving ambient and experimental (ambient + 3 g N m-2 yr-1) nitrate deposition. Prior to placing litterbags in the field, half of the bags were sterilized to eliminate the resident microbial community. Results demonstrated that suppression of soil respiration is not associated with process alterations in the forest floor. Differences were instead associated with significantly higher (146.5 μmol C m-2 s-1) litter-free soil respiration rates in the ambient N deposition sites versus the experimental N deposition sites (105.2 μmol C m-2 s-1). The treatments had little effect on potential DOC production from litter in the first 230 days, but potential production was effectively doubled after 630 days in all litter produced under elevated N regardless of litter treatment. The treatments also had little effect on litter mass loss after 230 days. However, the decomposition of fresh litter produced under elevated N was significantly suppressed after 630 days. These results suggest that experimental NO3- deposition alters soil respiration by influencing microbial processes in mineral soil, but alters DOC export and decomposition via changes in litter biochemistry.
