Methane is an important greenhouse gas and its atmospheric concentration has almost tripled since pre-industrial times. It plays a central role in atmospheric oxidation chemistry and affects stratospheric ozone and water vapour levels. Most of the methane from natural sources in Earth's atmosphere is thought to originate from biological processes in anoxic environments. Here we demonstrate using stable carbon isotopes that methane is readily formed in situ in terrestrial plants under oxic conditions by a hitherto unrecognized process. Significant methane emissions from both intact plants and detached leaves were observed during incubation experiments in the laboratory and in the field. If our measurements are typical for short-lived biomass and scaled on a global basis, we estimate a methane source strength of 62-236 Tg yr(-1) for living plants and 1-7 Tg yr(-1) for plant litter (1 Tg = 10(12) g). We suggest that this newly identified source may have important implications for the global methane budget and may call for a reconsideration of the role of natural methane sources in past climate change.

Although fluorine in the form of fluoride minerals is the most abundant halogen in the Earth's crust, only 12 naturally occurring organofluorine compounds have so far been found, and how these are biosynthesized remains a mystery. Here we describe an enzymatic reaction that occurs in the bacterium Streptomyces cattleya and which catalyses the conversion of fluoride ion and S-adenosylmethionine (SAM) to 5'-fluoro-5'-deoxyfluoroadenosine (5'-FDA). To our knowledge, this is the first fluorinase enzyme to be identified, a discovery that opens up a new biotechnological opportunity for the preparation of organofluorine compounds.

Atmospheric chloromethane (CH3Cl) plays an important role in stratospheric ozone destruction, but many uncertainties exist regarding the strengths of its sources and sinks and particularly regarding the processes generating this naturally occurring gas. Evidence is presented here that CH3Cl is produced in many terrestrial environments by a common mechanism. Abiotic conversion of chloride to CH3Cl occurs readily in plant material, with the widespread plant component pectin acting as a methyl donor. Significant CH3Cl emissions from senescent and dead leaves were observed at ambient temperatures; those emissions rose dramatically when temperatures increased. This ubiquitous process acting in terrestrial ecosystems and during biomass burning could contribute the bulk of atmospheric CH3Cl.

Abstract. Atmospheric chloromethane (CH 3 Cl) plays an important role in stratospheric ozone destruction, but many uncertainties still exist regarding strengths of both sources and sinks and the processes leading to formation of this naturally occurring gas. Recent work has identified a novel chemical origin for CH 3 Cl, which can explain its production in a variety of terrestrial environments: the widespread structural component of plants, pectin, reacts readily with chloride ion to form CH 3 Cl at both ambient and elevated temperatures . It has been proposed that this abiotic chloride methylation process in terrestrial environments could be responsible for formation of a large proportion of atmospheric CH 3 Cl. However, more information is required to determine the global importance of this new source and its contribution to the atmospheric CH 3 Cl budget.