Litter Decomposition in Response to Nitrogen Addition and Soil Warming at Harvard Forest 2010-2012

The purpose of this study is to examine whether two environmental change stressors (warming and nitrogen deposition) differentially impact litter decomposition. We investigated this using a two year litterbag decomposition experiment at the chronic N amendment experiment and the Barre Woods Soil warming experiment, and measured litter decay dynamics, enzyme activities and litter chemistry. In both years mass loss of the mixed litter was suppressed under N addition, with most of the mass loss observed in the first year compared to the second year (70% and 30% of total mass loss, respectively). Both years showed either increased activity for some hydrolytic enzymes (e.g. cellobiohydrolase) or no difference (e.g. ß-N-acetylglucosaminidase) with increased N. The lignolytic enzymes (e.g. peroxidases) showed no difference in activity in the first year, but had a highly reduced activity in year 2 under elevated N conditions. Soil warming did not significantly affect litter mass loss, and only had an effect on the activity of a few enzymes. In the oak reciprocal litterbag study, decay of oak litter originating from the highest N addition plot was negatively affected by simulated N deposition in the first year of decomposition, while after two years, simulated N deposition negatively affected all litter, and litter originating from the highest N addition plot decayed more slowly than control litter even without added N (i.e. in the control plot). In addition, in the first year of decomposition lignolytic enzyme activities were suppressed in litter originating from the N addition treatments, but due to simulated N deposition in year two.