Divergent drivers of the microbial methane sink in temperate forest and grassland soils

Abstract

Aerated topsoils are important sinks for atmospheric methane (CH4) via oxidation by CH4‐oxidizing bacteria (MOB). However, intensified management of grasslands and forests may reduce the CH4 sink capacity of soils. We investigated the influence of grassland land‐use intensity (150 sites) and forest management type (149 sites) on potential atmospheric CH4 oxidation rates (PMORs) and the abundance and diversity of MOB (with qPCR) in topsoils of three temperate regions in Germany. PMORs measurements in microcosms under defined conditions yielded approximately twice as much CH4 oxidation in forest than in grassland soils. High land‐use intensity of grasslands had a negative effect on PMORs (−40%) in almost all regions and fertilization was the predominant factor of grassland land‐use intensity leading to PMOR reduction by 20%. In contrast, forest management did not affect PMORs in forest soils. Upland soil cluster (USC)‐α was the dominant group of MOBs in the forests. In contrast, USC‐γ was absent in more than half of the forest soils but present in almost all grassland soils. USC‐α abundance had a direct positive effect on PMOR in forest, while in grasslands USC‐α and USC‐γ abundance affected PMOR positively with a more pronounced contribution of USC‐γ than USC‐α. Soil bulk density negatively influenced PMOR in both forests and grasslands. We further found that the response of the PMORs to pH, soil texture, soil water holding capacity and organic carbon and nitrogen content differ between temperate forest and grassland soils. pH had no direct effects on PMOR, but indirect ones via the MOB abundances, showing a negative effect on USC‐α, and a positive on USC‐γ abundance. We conclude that reduction in grassland land‐use intensity and afforestation has the potential to increase the CH4 sink function of soils and that different parameters determine the microbial methane sink in forest and grassland soils.

Microbial community composition in the rhizosphere of Larix decidua under different light regimes with additional focus on methane cycling microorganisms

“…Additionally, of USCα methanotrophs which are characterized by pmoA genes that distantly cluster from known methanotrophs 51 , 52 a draft genome has been recovered from forest soils via metagenomics sequencing methods and shedded light on CH 4 metabolic potential and environmental adaptions 53 . The derived high affinity for CH 4 and potential to oxidize atmospheric CH 4 concentrations was especially proposed for upland soils, mainly for acidic soils 12 , 15 , 16 , making USCα a major biological sink of CH 4 in forest soils 54 , 55 . Furthermore, methanotrophic Beijerinckiaceae strains to which members of the USCα belong were mostly isolated from peatlands or forest soils 12 .…”

Transcriptional dynamics of methane-cycling microbiomes are linked to seasonal CH4 fluxes in two hydromorphic and organic-rich grassland soils

“…Gas concentrations were measured on an Agilent 7890 gas chromatograph equipped with a flame ionization detector (for CH4) coupled with a methanizer (for CO2) (Agilent Technologies Inc., Santa Clara, CA, USA). Gas flux rates were calculated by the slope of the regression line of a linear regression of the gas concentration against time [17].…”

“…However, it is not fully understood which microorganisms oxidize CH4 at atmospheric concentrations in soils. Bacteria of upland soil clusters (USC-α) and USC-γ have been identified as likely important atmospheric CH4 oxidizers in upland soils [12,17,18], while well-known methanotrophic lineages also account for CH4 oxidation in anoxic paddy soils [19].…”

Nitrogen addition decreases methane uptake caused by methanotroph and methanogen imbalances in a Moso bamboo forest

“…Previous studies have demonstrated that the abundance, diversity, and community structure of methanotrophs and methanogens are mainly influenced by soil pH 51,52 , NH 4 + concentration 16 , and soil substrate 53 . For example, pH has a negative effect on upland soil cluster (USC)-α and a positive effect on USC-γ abundance 54 . USC-α has been detected in mostly acidic upland soils 55 , whereas USC-γ is detected in alkaline upland soils 56,57 .…”

“…USC-α has been detected in mostly acidic upland soils 55 , whereas USC-γ is detected in alkaline upland soils 56,57 . Furthermore, few studies have linked CH 4 fluxes to the abundances of methanotrophs and methanogens and the environmental factors influencing their abundances 54 . Thus, it is equally important to investigate N deposition on the relationship between soil CH 4 flux and the abundance and community structure of the methanotrophs and methanogens in Moso bamboo forests.…”