Methane is an important greenhouse gas that is produced and consumed in soils by microorganisms. Soils play an important role in the global methane cycle as soils can be methane sources and/or sinks depending on abiotic and biotic parameters. Until recently, studies of the contribution of plants to the global methane flux have focused on the role of plants as conduits for soil-borne methane emissions from wetlands. Barely examined to date are the influence of plants on methane flux and the presence of methanogenic and methanotrophic microorganisms in aerobic upland soils. The present study used soils from two grassland sites located in the Inn Valley in Northern Tyrol at ~750 m a.s.l. Soil sites were chosen to represent soils from siliceous and calcareous bedrock. Besides in situ methane measurements and profound soil microbiology analyses, labscale gas measurements were performed. In special pots with sieved soils from the study sites, two site typical plants Poa pratensis and Plantago lanceolata were grown from surface sterilized seeds in six parallel pots per soil site. To determine methane flux from soil itself, pots without plant coverage were analyzed as well. The pots were incubated at 10, 25 and 37° C and water content was kept at in situ conditions by rewetting with a.deion. To measure methane flux, the pots were closed with special plastic-hoods. Gas samples were withdrawn through inserted septa at the top of the plastic hoods and subsequently analyzed on CH4 and CO2 by gas chromatography. In our investigations, we could prove a distinct influence of plants on methane fluxes in upland soils on a lab-scale basis. Temperature was a crucial factor that influenced the effect of plants on the methane flux significantly. At 25° C Poa pratensis showed significant lower methane oxidation rates than soils covered with Plantago lanceolata and uncovered soil whereas no significant difference could be detected between flux measurements of the pots from siliceous bedrock and those of calcareous parent material. Our data proved not only a clear influence of plants on methane flux in grassland soils in comparison to uncovered soil but between the investigated plants as well. The study emphasizes the need to better resolve the influence of plants on the methane cycle and its involved microorganisms. Future studies will focus on microbial and molecular studies that should give an insight in how the differences in the net methane flux measurements are reflected in community compositions of methanogenic and methanotrophic microorganisms.
