Effects of mixing and various temperature regimes on the respiration of fresh and air-dried coniferous raw humus materials

O₂ uptake of fresh and air-dried L. F and H layer materials from a coniferous-forest floor was studied in the laboratory under regimes of progressively-increasing temperature and also at constant temperature. Experiments were carried out on separate materials from each layer and on mixtures of these materials. A marked apparent “priming” of microbial activity was found when previously air-dried materials were mixed and then rewetted. Some evidence of “priming” was also found when fresh L. F and H layer materials which had not been air dried were mixed. There were large differences between the O₂ uptake patterns of the fresh and air-dried materials when incubated in the same manner. Microbial activity in fresh materials was found to be stimulated when the same number of accumulated heat units were provided under a regime of increasing temperatures as compared to a regime of constant temperature. Results of the respiration studies are discussed in the light of possible differences in species diversity of the soil microbial population resulting from treatment of these organic horizon materials.