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

摘要

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)-alpha was the dominant group of MOBs in the forests. In contrast, USC-gamma was absent in more than half of the forest soils but present in almost all grassland soils. USC-alpha abundance had a direct positive effect on PMOR in forest, while in grasslands USC-alpha and USC-gamma abundance affected PMOR positively with a more pronounced contribution of USC-gamma than USC-alpha. 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-alpha, and a positive on USC-gamma 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.