A critical temperature threshold for early Acer rubrum leaf litter decomposition

Background/Question/Methods

Freshly senesced leaf litter contains a large quantity of labile carbon (C) that is rapidly consumed by microorganisms during early decomposition, (< 20% litter mass loss). Microbial decomposition is highly sensitive to temperature, and warming could accelerate decomposition rates. However, we know little about the dynamic relationship between temperature and microbial activity during the initial breakdown of labile C in freshly senesced leaf litter. To better understand how microorganisms respond to temperature changes in early decomposition, we asked: how does temperature affect C mineralization rates during the early stage of Acer rubrum litter decay in a temperate deciduous forest? We conducted a study in the Oak Openings Preserve Metropark of Northwest Ohio in November 2011 and measured CO₂ efflux on freshly senesced Acer rubrum leaf litter daily over the first 27 days of decomposition. Five replicate plots were constructed approximately 50 meters apart and arranged in a 2 x 2 factorial design with a soil-only control, soil + leaf litter treatment, soil+ added moisture control, and soil + litter + moisture treatment.

Results/Conclusions

We found that when leaf litter was added, respiration rates during the first month of decomposition were significantly higher than respiration without added leaf litter (P < 0.05). We observed a rapid acceleration in C mineralization from 9-11°C. Litter respiration rates doubled from 0.15 g C/cm²/day at 6-8°C to 0.30 g C/cm²/day at 9-11°C, with increasing variability at higher temperatures. These results suggest that microbial activity on decomposing litter was temperature limited below 9 °C, while other driving factors, such as litter chemistry and nutrient availability, may have played a major role in determining decay rates above 9 °C. Furthermore, within the 9-11°C range, soil + litter Q₁₀ values were more than double the values for soil alone (23 and 11, respectively), indicating that respiration from decomposing litter is more temperature sensitive than from soil organic matter decomposition. We conclude that there is a critical temperature threshold for Acer rubrum decomposition between 9-11°C.