Sink or Source: Alternative Roles of Glacier Foreland Meadow Soils in Methane Emission Is Regulated by Glacier Melting on the Tibetan Plateau

Abstract

Glacier foreland soils have long been considered as methane (CH4) sinks. However, they are flooded by glacial meltwater annually during the glacier melting season, altering their redox potential. The impacts of this annual flooding on CH4 emission dynamics and methane-cycling microorganisms are not well understood. Herein, we measured in situ methane flux in glacier foreland soils during the pre-melting and melting seasons on the Tibetan Plateau. In addition, high-throughput sequencing and qPCR were used to investigate the diversity, taxonomic composition, and the abundance of methanogenic archaea and methanotrophic bacteria. Our results showed that the methane flux ranged from −10.11 to 4.81 μg·m−2·h−1 in the pre-melting season, and increased to 7.48–22.57 μg·m−2·h−1 in the melting season. This indicates that glacier foreland soils change from a methane sink to a methane source under the impact of glacial meltwater. The extent of methane flux depends on methane production and oxidation conducted by methanogens and methanotrophs. Among all the environmental factors, pH (but not moisture) is dominant for methanogens, while both pH and moisture are not that strong for methanotrophs. The dominant methanotrophs were Methylobacter and Methylocystis, whereas the methanogens were dominated by methylotrophic Methanomassiliicoccales and hydrogenotrophic Methanomicrobiales. Their distributions were also affected by microtopography and environmental factor differences. This study reveals an alternative role of glacier foreland meadow soils as both methane sink and source, which is regulated by the annual glacial melt. This suggests enhanced glacial retreat may positively feedback global warming by increasing methane emission in glacier foreland soils in the context of climate change.

Salinity causes differences in stratigraphic methane sources and sinks

“…Iron and manganese content was determined by inductively coupled plasma mass spectrometry (ICP–MS) [ 48 ]. Moisture was measured by the gravimetric method as described previously [ 49 ]. The soil organic matter (OM) content was determined by the potassium dichromate oxidation method with air-dried soils.…”

Grazing exclusion alters soil methane flux and methanotrophic and methanogenic communities in alpine meadows on the Qinghai–Tibet Plateau

“…In the plots, 12 chambers were installed and vegetation was cut. CH 4 flux was measured at 9:00–11:00 daily for 1 week, and the gas in the box was collected using a syringe every 15 min ( Xing et al, 2022 ). The box was covered with a white insulating foam during sampling to avoid the warming effect of sunlight ( Zhang et al, 2013 ).…”

“…CH 4 was tested using a flame ionization detector, and N 2 was used as the carrier gas to remove O 2 and water vapor ( Chen et al, 2017 ). The CH 4 flux was calculated according to the method reported by Xing et al (2022) .…”

Potential Effects of Methane Metabolic Microbial Communities on the Glacial Methane Budget in the Northwestern Tibetan Plateau

“…During glacial melting season, cryoconite holes, subglacial sediments, glacial meltwater at the terminus, and glacier runoff in the northern, southern, and southeastern regions of the TP are possible sources of CH 4 [7,12]. The permafrost rivers in the eastern TP are weak sources of CH 4 [33], whereas soil at glacier forelands in the northern regions is a potential source that might transform from a sink into a source of CH 4 [34]. However, research on the influence of CH 4 -metabolic microbial communities within glaciers on the CH 4 budget remains scarce, especially for the northwestern TP regions.…”