Effects of warming on decomposition of submerged plant litter and associated microorganisms in streamside channels

Surface air temperatures are predicted to increase in the near future, which will likely affect microbial activity and carbon flow in stream ecosystems. I performed an experiment in streamside channels at Coweeta Hydrological Laboratory, NC to assess responses of litter-associated microorganisms to moderate increases in water temperature (5 levels, ambient to +4°C). The objectives of the experiment were to determine: (1) if there are differences in the magnitude of responses to temperature among various microbial parameters and (2) whether microbial responses to temperature vary among plant litter of different carbon quality. Thus, I measured litter decomposition rate, fungal biomass (ergosterol), fungal growth rate, fungal and bacterial production (radiolabeled tracers) and microbial respiration associated with submerged decaying Acer rubrum and Rhododendron maximum leaf litter, Quercus alba wood and Liquidambar styraciflua leaf litter grown at ambient and elevated CO2 levels. Fungal growth rate and microbial respiration responded to temperature increases in a similar way and were highly sensitive to warming at relatively low water temperatures, while litter decomposition rate tended to be less sensitive. Estimates of temperature sensitivity of microbial parameters (apparent activation energy) were greater (often ca. 1 eV) than those typically reported for respiratory complex (ca. 0.65 eV). Temperature increases affected microbial activity onsubstrates of different carbon quality in a similar way. Under the current climate change predictions these trends portend important implications for the future of stream ecosystems, since microbial activity tends to be more sensitive to temperature changes during the coldest season (autumn-winter) when leaf litter standing stock and associated microbial activity are at their peak