Epsilon Archive for Student Projects

Abstract

The increasing threat of climate change has led to a increased need for models to predict future climat. In these models the changes in the soil carbon pools due to changes in microbiel degradation of the organic matter can lead to both positive and negative feedback-effects. There is however a lack of consensues on the temperature respons on degradation soil organic matter. This paper aim to give a better understanding on the factors controlling the temperature respons. The factors studied were the carbon substrate qualitity and the physiological status of the microorganisms. The soil used as a model system was the mor-layer collected from a spruce dominated forest in Umeå. Different carbon sources together with nitrogen and phosforous were added to the soil and the respiration was measured with a respirometer. Each combination of carbon source and temperature was replicated 4 times at each of the temperatures, 4, 9, 14, and 19 degrees Celsius. Parameter values for each of the different physiological stages in microbial growth, base respiration, substrate induced respiration, exponential growth (my) and lag time, was extracted from the data.

The results indicateted differences in the temperature response both for the different carbon substrates and the different microbial growth stages. The more recalcitrant carbon substrate along with base respiration, in this case microbial growth on humus, displayed the lowest temperature responses, Q10-values of less than 2,5, while the more labile sugars displayed Q10-values from 2,5 and up to 4. Exponential growth (my) and base respiration was the physiological stages with the lowest Q10 while the substrate induced respiration and lag time showed generally higher Q10-values. The results indicate that the temperature response is dependent on both the physiological growth stage and the carbon substrate quality, with lower Q10 for the more recalcitrant sources.