In a recent study published in PNAS, a research team led by Prof. YANG Yuanhe from the Institute of Botany of the Chinese Academy of Sciences, provides compelling evidence that microbial carbon use efficiency (CUE; the proportion of C uptake used for microbial growth) increases after abrupt permafrost thaw.

Employing a substrate-independent ¹⁸O tracing approach, the researchers examined how microbial CUE changes after abrupt permafrost thaw. They collected the topsoil samples from a permafrost thaw sequence, and also from five additional thaw-affected sites on the Tibetan Plateau.

The results from both the thaw sequence and the regional-scale sites consistently revealed that microbial CUE increased after permafrost thaw, demonstrating the generality of the finding.

Further analyses revealed that the increase in microbial CUE was primarily due to the changes in microbial community composition: a larger biomass of fungi relative to bacteria and more fast-growing taxa in thawed area.

Moreover, the elevated soil phosphorus availability upon permafrost thaw could provide microorganisms with necessary nutrients to synthesize essential cell components, further promoting microbial growth and resulting in higher microbial CUE.

Abrupt permafrost thaw is generally considered as a trigger for substantial greenhouse gas emission and thus a positive permafrost carbon-climate feedback. However, the permafrost thaw-induced increase in microbial CUE observed here would potentially promote the incorporation of microbial-derived compounds into soil, consequently stimulating the formation of stable soil carbon and weakening the strength of carbon-climate feedback.

This study sheds light on how abrupt permafrost thaw affects microbial CUE, and highlights the importance of considering the dynamics of microbial physiology to better understand permafrost carbon fate.

 Increased microbial carbon use efficiency driven by altered microbial community composition and improved soil phosphorus availability. (Image by QIN Shuqi)