Warming alters surface soil organic matter composition despite unchanged carbon stocks in a Tibetan permafrost ecosystem

Fei Li, Yunfeng Peng, Leiyi Chen, Guibiao Yang, Benjamin W. Abbott, Dianye Zhang, Kai Fang, Guanqin Wang, Jun Wang, Jianchun Yu, Li Liu, Qiwen Zhang, Kelong Chen, Anwar Mohammat and Yuanhe Yang

Proposed conceptual model of warming effects on surface soil organic carbon (SOC) stocks and their compositions. Image provided by authors.
Proposed conceptual model of warming effects on surface soil organic carbon (SOC) stocks and their compositions. Image provided by authors.

Permafrost ecosystems, mainly distributed in high-latitude and high-altitude regions, are very sensitive to climate warming. A warmer climate could alter carbon (C) inputs and outputs in these ecosystems, and thus induce changes in soil organic carbon (SOC) stocks. However, experimental evidence about warming effects on SOC stocks is still lacking in permafrost ecosystems. In particular, it remains unclear whether and how climate warming will modify the composition of soil organic matter (SOM).

Here we quantified the responses to experimental warming of C inputs via vegetation production, C losses via soil respiration, and SOC stocks in the top 30 cm in a typical permafrost ecosystem on the Tibetan Plateau. We then characterized the dynamics of SOM composition using 13C nuclear magnetic resonance and biomarker analyses. We further measured microbial community composition and soil extracellular enzyme activity to explore the potential mechanisms responsible for SOC dynamics.

Based on field and laboratory measurements across three growing seasons during 2014-2016, we found that warming significantly stimulated root biomass and heterotrophic respiration (i.e. respiration of soil organisms and microbes). The increased ecosystem C inputs (root biomass) and outputs (respiration) may counterbalance each other, resulting in non-significant changes in SOC stocks. However, warming altered the SOM composition in the top 10 cm during the fourth experimental year. It increased the abundance of alkyl C component, but decreased aromatic C, primarily lignin (one of the main constituents of wood). The decrease in the abundance of lignin-derived compounds was largely driven by the increased soil phenol oxidase activity under warming treatment. These results demonstrate that Tibetan permafrost ecosystem SOC stocks are vulnerable to climate warming, which may in turn trigger a positive C–climate feedback in a warmer world.

Read the paper in full here.

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