In the next one hundred years, increasing nitrogen deposition and higher temperatures due to climate change could profoundly alter the decomposition of woody debris in New England forests.  In addition, these environmental changes are predicted to shift the species composition of these forests, thus influencing the quality of the woody debris pool.  Previous research has shown that warming, nitrogen addition and litter quality all individually influence decomposition by the microbial community.  However, it is not known how these variables will interact to modify the decomposition of woody debris.  Here we quantified the interactive effects of nitrogen addition, soil warming and carbon quality on the decomposition of woody debris in an eight-week lab study.  We used wood shavings of two New England tree species with varying lignin contents: Tsuga canadensis (high lignin) and Betula lenta (low lignin).  Wood shavings were mixed with soil in a ratio of 1:3 in small pots.  We then exposed the differing substrates to two nitrogen treatments (ambient and nitrogen addition added as 35.7 mg ammonium nitrate per week) and two warming treatments (20ºC and 25ºC).  Carbon dioxide efflux from the differing substrates was measured on a weekly basis using an Infrared Gas Analyzer.

Results/Conclusions

We found that substrate and temperature influenced decomposition rates, with the lower lignin B. lenta decomposing faster than T. canadensis, and both decomposing faster at higher temperatures.  We did not find an overall effect of nitrogen on decomposition; we did, however, find that the increased decomposition caused by warming was eliminated by nitrogen addition.  In addition, there was a trend towards the higher lignin T. canadensis having a suppressed decomposition under warming and nitrogen addition that was not seen with the lower lignin B. lenta.  These results suggest that though substrate and temperature are the major drivers of woody debris decomposition, nitrogen addition may interact with these variables to give differing results.