31 July 2023

In Tibetan permafrost 54% of the carbon comes from microbes


A Chinese study quantifies for the first time the weight of major soil organic carbon components released due to rising temperatures

by Matteo Cavallito


The thawing of the permafrost of the Tibetan Plateau, favoured by climate change, causes a dispersion of the organic carbon stored in the soil and expecially in the microbial necromass. This was revealed by a Chinese study published in the journal Environmental Science & Technology.

The investigation is particularly important as it reveals, for the first time, the weight of different organic sources of the element in the soil. Previous studies, underlines a statement by the Chinese Academy of Sciences, had shown the link between rising temperatures and the loss of the element from the soil, but the composition and characteristics of the organic carbon itself had not yet been described in detail.

The preeminence of microbes

Researchers, led by Kang Shichang, professor at the Academy’s Northwest Institute of Environment and Resources, collected soil samples in the northeastern Tibetan Plateau to study the variations of different components of organic carbon from two main sources: microorganisms and plants.

To estimate the weight of the different components, the scientists took into account two ‘markers’, namely amino sugars, which are associated with microbes, and lignin phenols, which are present in the plant mass.

The study was thus able to “provide direct evidence that microbial necromass carbon is a major component of lost carbon in a retrogressive permafrost thaw slump.”

The research

In summary: “The retrogressive thaw slump led to a ∼61% decrease in soil organic carbon (SOC),” the research explains. “As evident in the levels of amino sugars (average of 55.92 ± 18.79 mg g–1 of organic carbon, OC) and lignin phenols (average of 15.00 ± 8.05 mg g–1 OC), microbial-derived carbon (microbial necromass carbon) was the major component of the SOC loss, accounting for ∼54% of the SOC loss in the permafrost thaw slump.”

The researchers also found that changes in amino sugars were mainly related to pH, plant inputs and soil moisture content. Soil moisture content also influenced changes in lignin phenols.

Alpine permafrost is more vulnerable to climate change

The word ‘permafrost‘ refers to the type of perennially frozen (but not necessarily ice-covered) soil found in some cold regions. To date, according to an estimate quoted by the University of Arizona, this type of soil contains, on a global scale,“a whopping 1,500 trillion grams (1.5 billion tonnes, ed.) of SOC. That’s twice as much as what’s stored in the atmosphere.”

Much of this amount is located in the Arctic regions while a minority share, 85 million tonnes, is concentrated in the Alpine permafrost of which the Tibetan plateau represents the largest area.

The problem, said a research carried out last year by scientists of the University of Arizona, is that territories at lower latitudes are more vulnerable to the effects of climate change than those at the poles. Prediction models, in particular, suggest that under current global warming conditions, thawing would affect 20 per cent of the surface of Arctic permafrost and 60 per cent of that of Alpine permafrost in the future (but the time horizon is not defined).