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Effects of Possible Warming-Induced Increases in Freeze-Thaw Cycles on Soil Microbes
Haei, M., Rousk, J., Ilstedt, U., Oquist, M., Baath, E. and Laudon, H. 2011. Effects of soil frost on growth, composition and respiration of the soil microbial decomposer community. Soil Biology and Biochemistry 41: 2069-2077.

The authors write that "in addition to a general warming trend, most climate change models predict that the variability of weather fluctuations, including precipitation and temperature patterns, will increase in coming decades," and they say that at high-latitudes "the three primary regulators of microbial activity in soil -- substrate availability, temperature and moisture -- are all strongly influenced by freeze-thaw cycles," and that "any perturbations of freezing and freeze-thaw cycles may strongly influence the soil microbial community."

What was done
In a study designed to explore this possibility, Haei et al., as they describe it, "sampled riparian soil from a Swedish boreal forest and applied treatments with variations in four factors related to soil freezing (temperature, treatment duration, soil water content and frequency of freeze-thaw cycles), at three levels in a laboratory experiment" in which they measured "bacterial and fungal growth, basal respiration, soil microbial phospholipid fatty acid composition, and concentration of dissolved organic carbon."

What was learned
After analyzing the results of the many aspects of their investigation, the six scientists were forced to conclude that the number of freeze-thaw events had no effect on the microbial variables they studied, specifically noting that they "did not find any significant effects of the number of freeze-thawing cycles on the soil basal respiration rate," which findings they describe as being "compatible with those reported by Schimel and Clein (1996).

What it means
Contrary to several prior suppositions, Haei et al. conclude that the higher frequency of freeze-thaw events predicted to follow global warming -- if global warming ever kicks in and begins raising temperatures again, and if the predicted increase in freeze-thaw cycling ever occurs -- "will likely have a limited impact on soil microorganisms" and, therefore, the various ecosystem services they provide, which fortunately does not sound like a very threatening scenario.

Schimel, J.P. and Clein, J.S. 1996. Microbial response to freeze-thaw cycles in tundra and taiga soils. Soil Biology and Biochemistry 28: 1061-1066.

Reviewed 28 December 2011