The Effect of Temperature and Heat Treatment on Soil Metabolism

Summary The respiration of subantarctic and subtropical soils was found to increase as temperature increased from 100 to 37°C. The gas exchange decreased between 37° and 50°C., but increased with further increase in temperature. The oxygen uptake of soil subjected to various heat treatments showed an increase with the severity of treatment. The ratio of COa evolved to oxygen consumed of heat‐sterilized soil was always below 0.4, indicating a different oxidation process from that of unsterilized soils in which the ratio approximates 1.0. The activity of heat‐sterilized soil was not inhibited by NaCl, NaN 3 , or HgCl 2 , indicating that a non‐enzymic oxygen uptake and CO, evolution were occurring. Chemical oxidation also seems to occur in unsterilized soils at high temperatures, and is likely to be a factor in the decline in organic matter in dry, exposed soils. Oxidative enzymes of ‘dead’ micro‐organisms appear to be chiefly responsible for the immediate respiration on wetting an air‐dry soil.