CARBON-DIOXIDE AND METHANE FORMATION IN FOREST MINERAL AND PEAT SOILSDURING AEROBIC AND ANAEROBIC INCUBATIONS

Mineral and peat forest soils, sampled at three depths, were incubated aerobically and anaerobically at 16-degrees-C for 26 wk and were moni tored for CH4 and CO2 formation. Mean CO2 production rates were simila r under aerobic and anaerobic conditions in mineral subsoils with very low organic matter content, whereas in organic soils the rate was abo ut 10 times greater under aerobic than anaerobic conditions. The corre lations coefficient (r) between mean aerobic and mean anaerobic produc tion rates was 0.98, for the entire data set. Mineral and organic samp les incubated anaerobically both showed a decline in CO2 production ra te with increasing time of incubation. The decline was more strongly r elated to incubation time than to the absolute concentrations of CO2 i n the vials. The rates after 19 wk were approx. 10% of the initial rat es. This inhibition was largely offset by flushing the vials with N2 g as, indicating the volatile nature of the inhibiting substances. Altho ugh CO2 production rates increased immediately upon flushing, there we re still weak indications of a residual inhibiting effect. That, toget her with the rapid return of inhibition, suggested that non-volatile s ubstances were also involved. One implication of these results is that the activity in anaerobic field soils very much depends on the remova l of the inhibiting agents, e.g. by aeration during periodic draining of soil layers and by the movement of water through the soil. Methane formation occurred in most mor layers and peats. A well humified wood- Cyperaceae peat was, however, a notable exception. Methane production rates increased during the experimental period. The increasing CH4 pro duction rates, and the final (26 wk) measured rates, were approximatel y proportional to the frequency of anaerobic conditions in the origina l field situation.