In conjunction with the OP3 campaign in Danum Valley, Malaysian Borneo, flux measurements of methyl chloride (CH3Cl) and methyl bromide (CH3Br) were performed from both tropical plant branches and leaf litter in June and July 2008. Live plants were mainly from the Dipterocarpaceae family whilst leaf litter samples were representative mixtures of different plant species. Environmental parameters, including photosynthetically-active radiation, total solar radiation and air temperature, were also recorded. The dominant factor determining magnitude of methyl halide fluxes from living plants was plant species, with specimens of the genus Shorea showing persistent high emissions of both gases, e.g. Shorea pilosa: 65 ± 17 ng CH3Cl h-1 g-1 (dry weight foliage) and 2.7 ± 0.6 ng CH3Br h-1 g-1 (dry weight foliage). Mean CH3Cl and CH3Br emissions across 18 species of plant were 19 (range

Abstract. Fluxes of CH 3 Br and CH 3 Cl and their relationship with potential drivers such as sunlight, temperature and soil moisture, were monitored at fortnightly to monthly intervals for more than two years at two contrasting temperate salt marsh sites in Scotland. Manipulation experiments were conducted to further investigate possible links between drivers and fluxes. Fluxes followed both seasonal and diurnal trends with highest fluxes during summer days and lowest (negative) fluxes during winter nights. Mean (± 1 sd) annually and diurnally-weighted net emissions from the two sites were found to be 300 ± 44 ng m −2 h −1 for CH 3 Br and 662 ± 266 ng m −2 h −1 for CH 3 Cl. The fluxes from this work are similar to findings from this and other research groups for salt marshes in cooler, higher latitude climates, but lower than values from salt marshes in the Mediterranean climate of southern California. Statistical analysis generally did not demonstrate a strong link between temperature or sunlight levels and methyl halide fluxes, although it is likely that temperatures have a weak direct influence on emissions, and both certainly have indirect influence via the annual and daily cycles of the vegetation. CH 3 Cl flux magnitudes from different measurement locations depended on the plant species enclosed whereas such dependency was not discernible for CH 3 Br fluxes. In 14 out of 18 collars with vegetation CH 3 Br and CH 3 Cl net fluxes were significantly positively correlated. The CH 3 Cl/CH 3 Br net-emission mass ratio was 2.2, a magnitude lower than mass ratios of global methyl halide budgets (∼22) or emissions from tropical rainforests (∼60). This is likely due to preference for CH 3 Br production by the relatively high bromine content in the salt marsh plant material. Extrapolation based solely on data from this study yields Correspondence to: M. R. Heal (m.heal@ed.ac.uk) salt marsh contributions of 0.5-3.2% and 0.05-0.33%, respectively, of currently-estimated total global production of CH 3 Br and CH 3 Cl, but actual global contributions likely lie between these values and those derived from southern California.

The original report that plants emit methane (CH 4) under aerobic conditions caused much debate and controversy. Critics questioned experimental techniques, possible mechanisms for CH 4 production and the nature of estimating global emissions. Several studies have now confirmed that aerobic CH 4 emissions can be detected from plant foliage but the extent of the phenomenon in plants and the precise mechanisms and precursors involved remain uncertain. In this study, we investigated the role of environmentally realistic levels of ultraviolet (UV) radiation in causing the emission of CH 4 and other gases from foliage obtained from a wide variety of plant types. We related our measured emissions to the foliar content of methyl esters and lignin and to the epidermal UV absorbance of the species investigated. Our data demonstrate that the terrestrial vegetation foliage sampled did emit CH 4, with a range in emissions of 0.6–31.8 ng CH 4 g−1 leaf DW h−1, which compares favourably with the original reports of experimental work. In addition to CH 4 emissions, our data show that carbon monoxide, ethene and propane are also emitted under UV stress but we detected no significant emissions of carbon dioxide or ethane.

Oilseed rape (OSR, Brassica napus L.) is an important feedstock for biodiesel; hence, carbon dioxide (CO2), methane (CH4) and particularly fertilizer‐derived nitrous oxide (N2O) emissions during cultivation must be quantified to assess putative greenhouse gas (GHG) savings, thus creating an urgent and increasing need for such data. Substrates of nitrification [ammonium (NH4)] and denitrification [nitrate (NO3)], the predominant N2O production pathways, were supplied separately and in combination to OSR in a UK field trial aiming to: (i) produce an accurate GHG budget of fertilizer application; (ii) characterize short‐ to medium‐term variation in GHG fluxes; (iii) establish the processes driving N2O emission. Three treatments were applied twice, 1 week apart: ammonium nitrate fertilizer (NH4NO3, 69 kg‐N ha−1) mimicking the farm management, ammonium chloride (NH4Cl, 34.4 kg‐N ha−1) and sodium nitrate (NaNO3, 34.6 kg‐N ha−1). We deployed SkyLine2D for the very first time, a novel automated chamber system to measure CO2, CH4 and N2O fluxes at unprecedented high temporal and spatial resolution from OSR. During 3 weeks following the fertilizer application, CH4 fluxes were negligible, but all treatments were a net sink for CO2 (ca. 100 g CO2 m−2). Cumulative N2O emissions (ca. 120 g CO2‐eq m−2) from NH4NO3 were significantly greater (P < 0.04) than from NaNO3 (ca. 80 g CO2‐eq m−2), but did not differ from NH4Cl (ca. 100 g CO2‐eq m−2) and reduced the carbon sink of photosynthesis so that OSR was a net GHG source in the fertilizer treatment. Diurnal variation in N2O emissions, peaking in the afternoon, was more strongly associated with photosynthetically active radiation (PAR) than temperature. This suggests that the supply of carbon (C) from photosynthate may have been the key driver of the observed diurnal pattern in N2O emission and thus should be considered in future process‐based models of GHG emissions.

[1] Methyl bromide and methyl chloride fluxes were measured at several sites in a sub-arctic wetland near Abisko, Sweden (68°28 0 N 18°49 0 E) throughout the 2008 growing season. Averaged over 92 flux measurements the sub-arctic wetland was found to be a small net sink for CH 3 Br, with mean (±1 sd) uptake of À25 (±20) ng m À2 h À1 , but a small net source of CH 3 Cl with mean emissions of 400 (±1600) ng m À2 h À1. Seasonal trends were observed in both CH 3 Br and CH 3 Cl net fluxes, but diurnal trends for CH 3 Cl only, with peak emissions observed during the afternoon. CH 3 Cl fluxes differed significantly with hydrological status of measurement locations; however, no other substantial correlations were observed between fluxes and external parameters (air and soil temperature and PAR). This study shows that the single previous estimated sink flux for CH 3 Cl in tundra globally (derived from measurements in Alaska) requires revision, although not that for CH 3 Br.