Relative Importance of Physical Constraints on Decomposition

Abstract

Soil organic matter (SOM) stability is thought to be dependent almost entirely on temperature, moisture, and microbial dynamics. While soil physical factors are also known determinants of SOM decomposition, proportionally little work has attempted to determine how these factors could regulate future rates of CO2 release from soils under a changing climate. Here, paired lab-field experiments explore the effects of change in the physical environment and carbon dioxide (CO2) respiration of SOM in mineral soil from an 80-year old red spruce forest stand in Nova Scotia, Canada. Factors tested were substrate transport, solubilization, oxygen availability, and physical structure, and were performed using the following respective disturbance methodologies: electrokinetics, wetting, air-sparging, and abrasion and compaction. Most treatments drove change in SOM decomposition rates, and the effect of the disturbance usually decayed over several days. Interestingly, laboratory and field results differed strongly, and opposite responses were often observed for a given type of disturbance. Electrokinetics, or the movement of substrates independent of other disturbances, did not produce any change to the soil CO2 emission regime. Few studies have tackled the importance of physical controls on soil decomposition, but this is new and potentially important work for making accurate future predictions of terrestrial carbon cycling.

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