PARENT SESSION
Contributed Oral Session 107: Soil Biota and Communities
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 524 B, Level 5, Palais des congrès de Montréal

Temperature effects on respiration of a ¹⁴C-labelled substrate and decomposer community structure.

Cooper, Julia¹, Burton, David², Griffiths, Bryan³, Daniell, Tim³, ¹ Dalhousie University, Halifax, NS, Canada² Nova Scotia Agricultural College, Truro, NS, Canada³ Scottish Crop Research Institute, Dundee, UK

ABSTRACT- An experiment was conducted to study the effects of temperature on decomposition. Soils were incubated with and without ¹⁴C-labelled wheat at 5°C, 15°C, 25°C and 35°C for approximately 120 days. Evolution of ¹⁴C-CO₂ was monitored as well as total CO₂ respiration. On day 7, 14, 21, 55 and 120 the composition of the microbial community was studied by extraction of community DNA and analysis using terminal restriction fragment length polymorphism (T-RFLP). Temperature affected the rate of added ¹⁴C respiration with the 25°C and 35°C treatments respiring a higher percentage of added ¹⁴C per day (0.90%) than the 5°C (0.37%) and the 15°C (0.60%) treatments. However, when expressed as rate of ¹⁴C respired per degree-day, the 5°C treatment had a significantly higher respiration rate (0.075%) than the other three temperature treatments. Total respiration of CO₂ was affected in a similar way with highest rates per day for the warmest temperature treatments (14.2 mg C kg soil^-1 d^-1 at 35°C), but highest rates per degree-day for the coldest temperature treatment (0.75 mg C kg soil^-1 d^-1 at 5°C). These results suggest a shift in function of the microbial community with temperature. T-RFLP analysis indicates differences in microbial community structure at different temperatures with fungal communities more dominant at cooler temperatures. The respiration data is being fit to a single-pool and double-pool exponential decomposition model to estimate the size of the potentially mineralizable pool of carbon at the different temperatures. Differences in the structure and function of microbial communities at various temperatures could result in a temperature-dependent change in the size of the pool of labile carbon. In addition, temperature-dependent variations in the C:N ratio of the decomposer community and its carbon assimilation efficiency could result in variations in the proportion of labile carbon respired as CO₂.

Key words: decomposition, temperature, T-RFLP, microbial community structure