Climate warming induced permafrost thaw changes soil microbial communities

Background/Question/Methods

Climate warming has been reported to intensify thawing in northern circumpolar permafrost, one of the largest vulnerable carbon (C) pools that potentially lead to positive feedbacks to climate warming. Soil microbial community plays important roles in releasing the terrestrial C, yet the mechanisms and magnitudes of the C decomposition process is unclear. To reveal the effect of regional climate change induced permafrost thawing on soil microbial functions, soil microbial communities were collected in Eightmile Lake region, Alaska with a gradient of permafrost degenerations. At each of the minimal (Mi), moderate (Mo) and extensive (Ex) permafrost thawing sites, six soil cores (0~115cm) were taken as replicates, each separated into 6-7 fractions by depth. Microbial community DNA samples of soil fractions within active layer but below thaw depth (80 samples) were analyzed by a comprehensive functional gene array, GeoChip 4.2.

Results/Conclusions

Microbial community functional structures were significantly different (p < 0.006, adonis in Bray-Curtis distance) among three sites, indicating a strong impact of thawing on the soil microbial community. Moderate thawing caused negative disturbance on microbial functional community, indicated by the significantly decreased (p < 0.001, t-test) functional α-diversity in the Mo site compared with that in Mi site. The Ex site had lower functional α-diversity than the Mi site but higher (p = 0.003, t-test) than the Mo site, which might be a sign of microbial community adaptation to thawing. As for individual genes, eight of 33 GeoChip detected C degradation genes were substantially different (p<0.05, analysis of variance) among sites. The Mo site had the lowest overall C degradation gene abundance. Regardless of the significantly lower functional α-diversity in the Ex site than in the Mi site, the overall C degradation gene abundance had no difference between the two sites. This revealed that the microbial functional community in the Ex site shifted towards more efficient C degradation. These results demonstrates that the microbial functional structure change under permafrost thawing may be one of the mechanisms that cause more intense C decomposition at Northern permafrost regions, leading to positive feedbacks to climate change.