Three factors affect decomposition: biota, climate, and litter quality. Biotic effects are typically treated as a simple function of climate variables (e.g., the interaction between temperature and moisture). Theory now suggests that decomposition rates will be influenced by biotic resource histories and that these histories will alter ecosystem biogeochemical cycling. However, this research has not yet addressed the influence of climate history, a microbial community’s preference for 'optimal' temperature and moisture levels on the decomposition of a common litter. In this experiment, we determine the 'optimal' temperature and moisture regimes for three climatically- and geographically-distinct soils (arctic, temperate, tropical) by manipulating temperature and moisture in a 3 x 5 x 4 (soil type x moisture x temperature) full-factorial design in a laboratory-controlled, 100-day decomposition experiment.

Results/Conclusions

'Optimal' moisture and temperature conditions were determined by greatest cumulative litter mineralization after 100 days. Marked effects of climate history were evident as soils respired at different rates depending on temperature and moisture conditions. Arctic soils exhibited the greatest cumulative CO₂-C production at 15°C and 55% water holding capacity, which are similar to peak arctic growing season conditions. Temperate soils experienced minimal benefit from additional moisture and heat availability as their greatest cumulative CO₂-C production occurred at levels marginally higher than peak growing season conditions. Tropical soil microbial communities displayed a marked preference for conditions at 30°C and 85% water holding capacity. Additionally, previous research shows that temperate and arctic soils are the most responsive to temporal changes (Lloyd and Taylor 1994). However, data from this experiment suggest that arctic soils at high temperatures (e.g., 30°C) will respire less because most cold-adapted bacteria are not physiologically capable of decomposition mechanisms at this elevated temperature. Thus, the depressed respiration shown at high temperatures could be carried out by small communities of mesophilic bacteria in the arctic that thrive in 15°C to 40°C.  Overall, this experiment produced novel insights to a new theory, climate history, and the mechanisms of microbial resistance and adaptation in the context of climate change.