Frequent freeze-thaw cycles yield diminished yet resistant and responsive microbial communities in two temperate...

Few studies have been conducted on adaptations of microbial communities to low and fluctuating temperatures using environmentally relevant conditions. In this study, six Himalayan and two temperate soils were selected as candidates for low-temperature/freeze-thaw (FT)-adapted and susceptible soils, respectively. Redundancy analysis with forward selection was used to create a model of environmental parameters explaining variability in the initial microbial abundance and 4 °C activities. The best predictor was soil carbon, explaining more than 74% of data variability (P=0.002), despite significant differences in the soil characteristics and environmental history. We tested the hypothesis that the reproduced Himalayan FT fluctuations select physiologically similar communities in distinct soils. Microcosms were experimentally subjected to two separate 50 and 60 FT cycle (FTC) experiments. A significant decrease in abundance, 4 °C basal respiration and drastic rearrangements in community-level physiological profiles (CLPP) were observed in microcosms with temperate soils until 40 FTC. CLPP remained distinct from those of the Himalayan soils. Minor changes were observed in the Himalayan soils, confirming that microbial populations with physiological traits consistent with the noncontinuous permafrost conditions reside in the Himalayan soils, whereas the surviving temperate soil microorganisms actively adjusted to novel environmental conditions.