Atmospheric\nTrace\nGas Oxidizers Contribute to Soil\nCarbon Fixation Driven by Key Soil Conditions in Terrestrial Ecosystems

Microbial oxidizers of trace gases\nsuch as hydrogen (H<sub>2</sub>) and carbon monoxide (CO) are widely\ndistributed in soil\nmicrobial\ncommunities and play a vital role in modulating biogeochemical cycles.\nHowever, the contribution of trace gas oxidizers to soil carbon fixation\nand the driving environmental factors remain unclear, especially on\nlarge scales. Here, we utilized biogeochemical and genome-resolved\nmetagenomic profiling, assisted by machine learning analysis, to estimate\nthe contributions of trace gas oxidizers to soil carbon fixation and\nto predict the key environmental factors driving this process in soils\nfrom five distinct ecosystems. The results showed that phylogenetically\nand physiologically diverse H<sub>2</sub> and CO oxidizers and chemosynthetic\ncarbon-fixing microbes are present in the soil in different terrestrial\necosystems. The large-scale variations in soil carbon fixation were\nhighly positively correlated with both the abundance and the activity\nof H<sub>2</sub> and CO oxidizers (<i>p</i> < 0.05–0.001).\nFurthermore, soil pH and moisture-induced shifts in the abundance\nof H<sub>2</sub> and CO oxidizers partially explained the variation\nin soil carbon fixation (55%). The contributions of trace gas oxidizers\nto soil carbon fixation in the different terrestrial ecosystems were\nestimated to range from 1.1% to 35.0%. The estimated rate of trace\ngas carbon fixation varied from 0.04 to 1.56 mg kg<sup>–1</sup> d<sup>–1</sup>. These findings reveal that atmospheric trace\ngas oxidizers may contribute to soil carbon fixation driven by key\nsoil environmental factors, highlighting the non-negligible contribution\nof these microbes to terrestrial carbon cycling.