HR: 1340h
AN: B23D-1610    [Abstracts]
TI: Influence of Soil Organic Matter Stabilization Mechanisms on Temperature Sensitivity of Soil Respiration
AU: Gillabel, J
EM: jeroen.gillabel@biw.kuleuven.be
AF: Division Soil and Water Management, Department of Earth and Environmental Sciences, K.U.Leuven, Kasteelpark Arenberg 20, Heverlee, 3010, Belgium
AU: De Gryze, S
EM: sdegryze@ucdavis.edu
AF: Agroecology Lab, Department of Plant Sciences, UC Davis, 1 Shields Avenue, Davis, Ca 95616, United States
AU: * Six, J
EM: jwsix@ucdavis.edu
AF: Agroecology Lab, Department of Plant Sciences, UC Davis, 1 Shields Avenue, Davis, Ca 95616, United States
AU: Merckx, R
EM: roel.merckx@biw.kuleuven.be
AF: Division Soil and Water Management, Department of Earth and Environmental Sciences, K.U.Leuven, Kasteelpark Arenberg 20, Heverlee, 3010, Belgium
AB: Knowledge on the sensitivity of soil organic matter (SOM) respiration to changes in temperature is crucial for predicting future impacts of climate change on soil C stocks. Temperature sensitivity of respiration is determined by the chemical structure of the compound to be decomposed and by the availability of the organic matter for decomposers. Biochemically recalcitrant SOM has a higher temperature sensitivity than biochemically labile SOM. However, it is hypothesized that the stabilization of SOM by interaction with the soil matrix could be an important attenuating control on temperature sensitivity. We investigated the effect of different SOM stabilization mechanisms on temperature sensitivity of SOM respiration. Two main mechanisms were considered: chemical interactions of SOM with clay and silt particles, and physical protection inside aggregates. Soil samples from an agricultural silt loam soil were fractionated by wet-sieving into macroaggregates, microaggregates and silt+clay fractions. SOM stabilization in the silt+clay fraction occurs mainly chemically, whereas in aggregates physical protection of SOM is more important. Samples of each fraction and of bulk soil were incubated at two temperatures (20°C and 30°C) for one month. After 2% of total soil carbon was respired, temperature sensitivity was determined for respiration of the next 0.5% of total soil carbon. This was done by calculating a Q10 value as the ratio of the times needed at each temperature to respire that fraction of the soil C. This method allows determination of temperature sensitivity independent of C quality. Calculated Q10 values decreased in the order bulk soil > macroaggregates > microaggregates > silt+clay, with the difference between macroaggregate Q10 and silt+clay Q10 being the only significant difference. These results indicate that protection of SOM attenuates temperature sensitivity, with chemical protection (silt+clay) having a larger effect than physical protection (aggregates).
DE: 0428 Carbon cycling (4806)
DE: 1630 Impacts of global change (1225)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting