Soil organic carbon (SOC) is a primary regulator of the forest–climate feedback. However, its indicative capability for the soil CH4 sink is poorly understood due to the incomplete knowledge of the underlying mechanisms. Therefore, SOC is not explicitly included in the current model estimation of the global forest CH4 sink. Here, using in-situ observations, global meta-analysis, and process-based modeling, we provide evidence that SOC constitutes an important variable that governs the forest CH4 sink. We find that a CH4 sink is enhanced with increasing SOC content on regional and global scales. The revised model with SOC function better reproduces the field observation and estimates a 39% larger global forest CH4 sink (24.27 Tg CH4 yr−1) than the model without considering SOC effects (17.46 Tg CH4 yr−1). This study highlights the role of SOC in the forest CH4 sink, which shall be factored into future global CH4 budget quantification.
CH4 emission in the Arctic has large uncertainty
due
to the lack of mechanistic understanding of the processes. CH4 oxidation in Arctic soil plays a critical role in the process,
whereby removal of up to 90% of CH4 produced in soils by
methanotrophs can occur before it reaches the atmosphere. Previous
studies have reported on the importance of rising temperatures in
CH4 oxidation, but because the Arctic is typically an N-limited
system, fewer studies on the effects of inorganic nitrogen (N) have
been reported. However, climate change and an increase of available
N caused by anthropogenic activities have recently been reported,
which may cause a drastic change in CH4 oxidation in Arctic
soils. In this study, we demonstrate that excessive levels of available
N in soil cause an increase in net CH4 emissions via the
reduction of CH4 oxidation in surface soil in the Arctic
tundra. In vitro experiments suggested that N in the form of NO3
– is responsible for the decrease in CH4 oxidation via influencing soil bacterial and methanotrophic
communities. The findings of our meta-analysis suggest that CH4 oxidation in the boreal biome is more susceptible to the
addition of N than in other biomes. We provide evidence that CH4 emissions in Arctic tundra can be enhanced by an increase
of available N, with profound implications for modeling CH4 dynamics in Arctic regions.
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