Abstract
Cloud forests are unique yet understudied ecosystems regarding CH(4) exchange despite their significance in carbon storage. We investigated CH(4) fluxes in peat soil and tree stems of two tropical cloud forests on Réunion Island, one featuring Erica reunionensis and the second a mix of E. reunionensis and Alsophila glaucifolia. The study examined microbiomes across below-ground (soil) and above-ground (canopy soil, leaves, and stems) forest compartments. Metagenomics and qPCR analyses targeted key genes in methanogenesis and methanotrophy in soil and above-ground samples, alongside soil physicochemical measurements. CH(4) fluxes from peat soil and tree stems were measured using gas chromatography and portable trace gas analyzers. Peat soil in both forests acted as a CH(4) sink (- 23.8 ± 4.84 µg C m(- 2) h(- 1)) and CO(2) source (55.5 ± 5.51 µg C m(- 2) h(- 1)), with higher CH(4) uptake in sites dominated by endemic tree species E. reunionensis. In forest soils, a high abundance of n-DAMO 16 S rRNA gene (3.42 × 10(7) ± 7 × 10(6) copies/g dw) was associated with nitrate levels and higher rates of CH(4) uptake and CO(2) emissions. NC-10 bacteria (0.1-0.3%) were detected in only the Erica forest soil, verrucomicrobial methanotrophs (0.1-3.1%) only in the mixed forest soil, whereas alphaproteobacterial methanotrophs (0.1-3.3%) were present in all soils. Tree stems in both forests were weak sinks of CH(4) (-0.94 ± 0.4 µg C m(- 2) h(- 1)). The canopy soil hosted verrucomicrobial methanotrophs (0.1-0.3%). The leaves in both forests exhibited metabolic potential for CH(4) production, e.g., exhibiting high mcrA copy numbers (3.5 × 10(5) ± 2.3 × 10(5) copies/g dw). However, no CH(4)-cycling functional genes were detected in the stem core samples. Tropical cloud forest peat soils showed high anaerobic methanotrophy via the n-DAMO process, while aerobic methanotrophs were abundant in canopy soils. Leaves hosted methanotrophs but predominantly methanogens. These results highlight the significant differences between canopy and soil microbiomes in the CH(4) cycle, emphasizing the importance of above-ground microbiomes in forest CH(4) gas budgets.