Effects of hummock–hollow microtopography on soil microbial communities and their links to soil carbon cycling in a sedge peatland of the Changbai mountains

Abstract

In peatlands, hummock–hollow microtopography generates distinct environmental gradients, leading to significant variations in carbon emissions and stocks between hummocks and hollows. However, the influence of such microtopographic differences on soil microbial communities remains poorly understood, hindering a clear understanding of the mechanisms underlying microtopography-driven carbon cycling. Here, we used high-throughput sequencing to investigate how hummock-hollow microtopography affects bacterial and fungal communities, as well as their relationships with soil carbon emissions, in the sedge peatlands of the Changbai Mountains in Northeast China. Our results revealed that soil CO₂ and CH₄ emissions varied significantly across three microtopographic positions, with hummocks exhibiting the highest CO₂ emissions, whereas under-hummock and hollow soils presented higher CH₄ emissions than hummocks did. Bacterial community metrics displayed significant variations across microtopographic positions, with hummocks exhibiting higher bacterial Shannon indices, a greater abundance of the bacterial phylum Proteobacteria, and more complex co-occurrence networks, whereas Chloroflexi were more abundant in hollows and Bacteroidetes were more abundant in under-hummocks. In contrast, microtopography had no significant effect on fungal diversity, community composition, and co-occurrence networks. Partial least squares path models showed that microtopographic variations between hummocks and under-hummocks created divergent hydrothermal conditions, which in turn altered the availability of organic substrates and nutrients. These environmental differences further shape bacterial communities and thereby modulate the significant variations in carbon emissions across microtopographic positions. Our study highlights that microtopography-driven environmental heterogeneity primarily regulates bacterial but not fungal community dynamics and that this bacterial-mediated pathway constitutes a core mechanism shaping peatland carbon cycling.