methane in the biosphere is mainly produced by prokaryotic methanogenic archaea, biomass burning, coal and oil extraction, and to a lesser extent by eukaryotic plants. Here we demonstrate that saprotrophic fungi produce methane without the involvement of methanogenic archaea. Fluorescence in situ hybridization, confocal laser-scanning microscopy and quantitative realtime PCR confirm no contribution from microbial contamination or endosymbionts. our results suggest a common methane formation pathway in fungal cells under aerobic conditions and thus identify fungi as another source of methane in the environment. stable carbon isotope labelling experiments reveal methionine as a precursor of methane in fungi. These findings of an aerobic fungus-derived methane formation pathway open another avenue in methane research and will further assist with current efforts in the identification of the processes involved and their ecological implications.

Cryptogamic covers, which comprise some of the oldest forms of terrestrial life on Earth (Lenton & Huntingford, ), have recently been found to fix large amounts of nitrogen and carbon dioxide from the atmosphere (Elbert etal., ). Here we show that they are also greenhouse gas sources with large nitrous oxide (N2O) and small methane (CH4) emissions. Whilst N2O emission rates varied with temperature, humidity, and N deposition, an almost constant ratio with respect to respiratory CO2 emissions was observed for numerous lichens and bryophytes. We employed this ratio together with respiration data to calculate global and regional N2O emissions. If our laboratory measurements are typical for lichens and bryophytes living on ground and plant surfaces and scaled on a global basis, we estimate a N2O source strength of 0.32-0.59 Tg year(-1) for the global N2O emissions from cryptogamic covers. Thus, our emission estimate might account for 4-9% of the global N2O budget from natural terrestrial sources. In a wide range of arid and forested regions, cryptogamic covers appear to be the dominant source of N2O. We suggest that greenhouse gas emissions associated with this source might increase in the course of global change due to higher temperatures and enhanced nitrogen deposition

Abstract. Methane (CH 4 ), an important greenhouse gas that affects radiation balance and consequently the earth's climate, still has uncertainties in its sinks and sources. The world's oceans are considered to be a source of CH 4 to the atmosphere, although the biogeochemical processes involved in its formation are not fully understood. Several recent studies provided strong evidence of CH 4 production in oxic marine and freshwaters, but its source is still a topic of debate. Studies of CH 4 dynamics in surface waters of oceans and large lakes have concluded that pelagic CH 4 supersaturation cannot be sustained either by lateral inputs from littoral or benthic inputs alone. However, regional and temporal oversaturation of surface waters occurs frequently. This comprises the observation of a CH 4 oversaturating state within the surface mixed layer, sometimes also termed the "oceanic methane paradox". In this study we considered marine algae as a possible direct source of CH 4 . Therefore, the coccolithophore Emiliania huxleyi was grown under controlled laboratory conditions and supplemented with two 13 C-labeled carbon substrates, namely bicarbonate and a position-specific 13 C-labeled methionine (R-S-13 CH 3 ). The CH 4 production was 0.7 µg particular organic carbon (POC) g −1 d −1 , or 30 ng g −1 POC h −1 . After supplementation of the cultures with the 13 C-labeled substrate, the isotope label was observed in headspace CH 4 . Moreover, the absence of methanogenic archaea within the algal culture and the oxic conditions during CH 4 formation suggest that the widespread marine algae Emiliania huxleyi might contribute to the observed spatially and temporally restricted CH 4 oversaturation in ocean surface waters.