Since the start of the Anthropocene, northern seasonally frozen peatlands have been warming at a rate of 0.6 °C per decade, twice that of the Earth’s average rate, thereby triggering increased nitrogen mineralization with subsequent potentially large losses of nitrous oxide (N2O) to the atmosphere. In this context, we found that seasonally frozen peatlands are important N2O emission sources in the Northern Hemisphere, and the thawing periods are the hot moment of annual N2O emissions (0.79±0.29 mg N2O m-2 d-1). Seasonally frozen peatlands have high N2O emission potential, but thawing significantly stimulates the expression of genes encoding N2O-producing protein complexes, resulting in high N2O emissions during spring. The hot moment of N2O emissions that occurred in the seasonally frozen peatlands was higher than those from drained peatland forests, permafrost, and non-managed northern peatland. The observed emission flux is even higher than those of tropical forests, the World’s largest natural terrestrial N2O source. This hot moment converts seasonally frozen peatlands into an important N2O emission source when it is otherwise a sink. Neglecting these hot moment emissions may lead to an underestimation of N2O emissions representing about 1.1% of N2O emissions from natural sources.
As the other two major greenhouse gases, the fluxes of CH4 and CO2 emissions were measured throughout an entire year in the seasonally frozen peatland. Interestingly, in contrast to N2O, we found that the thawed periods were the hot moments for annual CH4 and CO2 emissions and that seasonally frozen peatlands may represent a net source of CH4 and CO2.
With the intensification of global warming, the rate of carbon degradation and nitrogen mineralization in peatlands will be greatly increased. It can be predicted from our study that the warming effect caused by hot moment N2O, CH4, and CO2 emissions in seasonally frozen peatlands may make peatlands a net source of warming; however, both anthropogenic and natural disturbances may accelerate this occurrence. Thus, it is important to protect peatlands for the sake of ecological security and climate change at a global scale.
However, our study of seasonally frozen peatlands is far from over. Based on the mechanism of N2O emission hot moment in these peatlands, we were curious about the potential variations of viruses.
As the world’s largest storage of terrestrial organic C stocks, the abundant and seasonally-available nutrients stored in these soils are the most important substrates for the growth of microorganisms. Viruses have no intrinsic metabolism, replicating by infecting and parasitizing the cellular machinery of their hosts. Consequently, the high diversity of bacteria, fungi, and protozoa in peatland soils can support a wide diversity of viruses. In addition, during peat thawing, organic substrates are released and become more accessible for microorganisms, which in turn can then be infected by viruses. Hence, the seasonally frozen peatland may be an important reservoir and potential source of both DNA and RNA viruses. As such, we have continued our research on seasonally frozen peatlands, with a focus on investigating the presence of DNA and RNA viruses.
We found that the seasonally frozen peatland could be an important reservoir of DNA and RNA viruses, and these might pose a serious yet overlooked threat to human and planetary health. Under the background of global warming, there was a “hot horizon” and “hot moment” of virus fluxes in the seasonally frozen peatland, with a potential impact on ecosystem functions, especially the carbon and nitrogen cycles. With permafrost melting under climate change, viruses will increasingly be released from peatland, which covers more than half of the total land area in the northern hemisphere. This could affect ecosystem functions and climate change in these climate-critical habitats.
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Very interesting work!