Effect of temperature stress on structure and function of the methanogenic archaeal community in a rice field soil

The effect of a brief (24 h) temperature shift to 4°C (low‐temperature stress) or 50°C (high‐temperature stress) was studied in methanogenic slurries of Italian rice field soil incubated at either constant 30°C or 15°C. Low‐temperature (low‐T) stress showed no effect in either the 30°C or the 15°C incubations. High‐temperature (high‐T) stress, on the other hand, generally resulted in an increase in the partial pressure of H 2 , and the concentrations of acetate and propionate, which accumulated to about 100–200 Pa, 4–6 mM and 0.7–0.9 mM, respectively. The increase in H 2 was transient for 8–15 days. The increases in acetate and propionate were transient for about 20 days only in the 30°C incubations, but persisted in the 15°C incubations until the end of the experiment. The high‐T stress did not result in inhibition of CH 4 production in the 30°C incubations, but transiently inhibited the 15°C incubations for about 25–30 days. The archaeal community in the soils was analyzed by terminal restriction fragment length polymorphism of the gene of the SSU rRNA. In the 15°C incubations, the relative gene frequency of members of the Methanosarcinaceae decreased over an incubation period of 54 days, while those of Methanosaetaceae and of methanogenic rice cluster I increased. Temperature stress, high‐T stress in particular, tended to reverse this trend. In the 30°C incubations, on the other hand, the relative gene frequency of archaeal members showed the opposite temporal trend or remained constant unlike the 15°C incubations. Again, high‐T stress tended to reverse these trends, but the observed effects were much smaller in the 30°C incubations than in the 15°C incubations. In conclusion, a brief high‐T stress affected structure and function of the methanogenic archaeal community of rice field soil.