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.
Highlights
The tropospheric concentration of methane (CH4) has increased by 150% since the beginning of the industrial era and its warming potential is 28 times higher than that of CO2 (Ciais et al, 2013)
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 marker have found that CH4-oxidizing bacteria (MOB) in topsoils of three temperate regions in Germany
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 Upland soil cluster (USC)-α, and a positive on USC-γ abundance
Summary
The tropospheric concentration of methane (CH4) has increased by 150% since the beginning of the industrial era and its warming potential is 28 times higher than that of CO2 (Ciais et al, 2013). Other MOB assumed to be involved in atmospheric CH4 oxidation are members of USC-γ, which was detected in neutral to alkaline upland soils and have recently been identified as the main methanotrophs in alpine grassland soils (Deng et al, 2019; Knief, 2015). Few studies have linked atmospheric CH4 oxidation to the abundances of the methanotrophic groups and the environmental factors influencing their abundances It has been found for different soils that the proportion of USC-α was positively correlated with CH4 uptake (Nazaries et al, 2013) and might be a key group of MOB contributing to the global atmospheric CH4 sink. We hypothesized that in grasslands, high management intensity (fertilization and/ or frequent grazing and mowing) will reduce CH4 oxidation rates due to higher availability of ammonium in soils and to greater soil compaction by machinery use and/or livestock trampling. We assume that soil environmental properties drive both CH4 uptake and the abundance of MOB in soils
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