Soil microbial community determines vulnerability of soil carbon exposed to warming in northern permafrost

Background/Question/Methods

The plant carbon (C) has been accumulated in permafrost over hundreds to thousands of years because the low temperature and saturated soil condition protect organic C from microbial decomposition. As a result, enormous soil organic carbon is stored in permafrost, and likely more labile and thus vulnerable to climate change compared to the organic C stored in other ecosystems. The recent warming over the past decades has been documented in the northern high-latitude region and is likely to continue during the 21^stcentury. Through microbial decomposition, the release of previously frozen soil C in permafrost to the atmosphere under warming scenarios is one of the most likely positive feedbacks from terrestrial ecosystems to climate change. However, little is known about responses of soil microbial community to warming in permafrost. Here, we utilized microarray-based GeoChip and other metagenomic techniques to investigate the early phase response of soil microbial community one year after the establishment of winter warming treatment at the experiment site in Interior Alaska, compared with the microbial responses after one year continuous experimental warming in Central Oklahoma.

Results/Conclusions

Though warming increased soil temperature and substrates at both sites, the soil microbial community compositions were only altered at the AK site. More genes involved in C and N cycles were stimulated by warming at the AK site with greater magnitudes compare to limited warming effects observed at the OK site. These warming induced changes at the AK site caused substantial alterations in ecosystem functions, e.g. higher degree of decomposition indicated by increased soil ¹³C content and enhanced plant N update as indicated by higher foliar and litter N mass, and eventually affect the ecosystem net C exchange. The quick early phase responses of soil microbial community observed at the AK site indicates a rapid atmosphere CO₂ accumulation after plant growth cannot completely offset the C release from increased microbial decomposition under warming. This study demonstrates the importance of integrating soil microbes into models to project future scenarios of climate changes in different ecosystems as soil microbial community may not necessarily react to substrate increase and violate most modeling assumptions, as shown at the OK site.