Urban park metagenomics highlights sediments as a potential hotspot for CH(4) and N(2)O emission across diverse habitats.

内容摘要

Urban areas contribute the vast majority of greenhouse gas (GHG) emissions, and urban greenspaces, including urban parks, are being established to promote environmental health by mitigating GHG emissions. However, the diversity of CH4 and N2O cycling genes and microbiomes in urban park ecosystems remains poorly understood. Here, we sampled five types of habitats in subtropical urban parks, including moss, sediment, soil, tree hole, and water, to explore the microbial communities and microbially mediated CH4 and N2O cycling processes using metagenomic sequencing. We found strongly positive biodiversity-ecosystem-functioning (BEF) relationships in nitrogen cycling functions, as well as in CH4 cycling, except in sediment, indicating the microbial community in the sediment had reached function saturation for CH4 cycling. CH4 cycling was driven by a few specific microbial genera, whereas many microorganisms participated in the denitrification process. Microbes in sediment exhibited the highest CH4 and N2O metabolic potential among the five habitats, especially for methanogenesis and N2O production processes. Significant positive correlations were observed between the mcrA and N2O cycling genes, suggesting methanogenesis could be coupled with denitrification. Environmental factors, such as dissolved oxygen, total nitrogen, and total carbon greatly affected microbial community composition and functional gene families. These results highlight that pond sediments are an overlooked potential source of CH4 and N2O emissions, which may undermine the role of urban greenspace in reducing GHG emissions. Reducing nitrogen pollution and eutrophication is recommended to mitigate CH4 and N2O emissions from pond sediments in urban environments.