We compared leaf, root, cellulose filter paper and wood decomposition rates over 38 months in acidic tussock tundra under increased nutrient availability (10 g N m² y^-1, 5 g P m² y^-1) and air temperature (5-6 ^oC) at Toolik Lake, Alaska. Nutrient additions and elevated growing season air temperature have been on going since 1989. Five treatments were compared: control (CT), warmed (GH), fertilized since 1996 (NP11), fertilized since 1989 (NP18), and warmed plus fertilized since 1989 (GHNP). The experiment began in July 2003; samples were collected in August of each year between 2003 and 2006. Betula nana leaf litter from treatment plots was placed in both treatment plots and a common garden to examine how environmental changes associated with treatments altered decomposition rates.

Results/Conclusions

The greatest impact was that GH and GHNP litter in treatment plots had reduced decomposition rates (20% more mass remaining) compared to the same litter within a common garden suggesting environmental conditions within the greenhouses slowed decomposition. Comparing decomposition rates between a common Betula nana litter and treatment litter within treatment plots NP11 litter in NP11 plots had 5% less mass remaining compared to the common litter.  However, little difference was observed in the NP18 plots.  Overall litter in GH and GHNP plots decomposed more slowly with 15% greater mass remaining.  Filter paper place aboveground decomposed very slowly in the GH and GHNP plots with 10-20% mass loss, respectively. Filter paper decomposition rates were greatest both above and belowground in NP11 and NP18 plots. Betula wooden dowels placed both above and belowground decomposed slowly with 3-10% mass loss. Dowels placed aboveground had a greater mass remaining compared to belowground samples.  Betula nana roots decomposition varied little between treatments with 25% mass loss.  Wooden dowels and filter paper placed belowground had consistent mass loss over the 3 plus year period. Materials place aboveground decomposed substantially over the first growing season, not much occurred during the following 2 years, but rates increased again during the final year. In conclusion, litter and soil characteristics in GH and GHNP plots decreased decomposition rates. Betula nana leaf litter decomposed the most rapidly (30-50% mass loss), following by Betula nana roots and finally wooden dowels. Filter paper decomposition was the most variable (10-90% mass loss).