Microbial mechanisms for CO and CH emissions in Robinia pseudoacacia forests along a North-South transect in the Loess Plateau.

Forest soil microbes play a crucial role in regulating atmospheric-soil carbon fluxes. Environmental heterogeneity across forest types and regions may lead to differences in soil CO and CH emissions. However, the microbial mechanisms underlying these emission variations are currently unclear. In this study, we measured CO and CH emissions of Robinia pseudoacacia forests along a north-south transect in the Loess Plateau. Using metagenomic sequencing, we investigated the structural and functional profiles of soil carbon cycling microbial communities. Results indicated that the forest CO emissions of Robinia pseudoacacia was significantly higher in the north region than in the south region, while the CH emission was oppositely. This is mainly attributed to changes in gene abundance driven by soil pH and moisture in participating carbon degradation and methane oxidation processes across different forest regions. The gene differences in carbon fixation processes between regions primarily stem from the Calvin cycle, where the abundance of rbcL, rbcS, and prkB genes dominates microbial carbon fixation in forest soils. Random forest models revealed key genes involved in predicting forest soil CO emissions, including SGA1 and amyA for starch decomposition, TYR for lignin decomposition, chitinase for chitin decomposition, and pectinesterase for pectin decomposition. Microbial functional characterization revealed that interregional differences in CH emissions during methane metabolism may originate from methane oxidation processes, and the associated gene abundances (glyA, ppc, and pmoB) were key genes for predicting CH emissions from forest soils. Our results provide new insights into the microbial mechanisms of CO and CH emissions from forest soils, which will be crucial for accurate prediction of the forest soil carbon cycle in the future.