Mode-specific chemisorption of CH4 on Pt{110}-(1 x 2) explored by first-principles molecular dynamics

The chemisorption of CH4 on Pt{110}-(1 x 2) has been studied by vibrational analysis of the reaction pathway defined by the potential energy surface and, in time reversal, by first-principles molecular dynamics simulations of CH4 associative desorption, with the electronic structure treated explicitly using density functional theory. We find that the symmetric stretch vibration ν1 is strongly coupled to the reaction coordinate; our results therefore provide a firm theoretical basis for recently reported state-resolved reactivity measurements, which show that excitation of the ν1 normal mode is the most efficient way to enhance the reaction probability

Impact of variation in structure of condensed tannins from sainfoin (Onobrychis viciifolia) on in vitro ruminal methan production and fermentation characteristics

Our study investigated the effects of condensed tannins (CT) on rumen in vitro methane (CH4) production and fermentation characteristics by incubating lucerne in buffered rumen fluid in combination with different CT extracts at 0 (control), 40, 80 and 120 g CT/kg of substrate DM. Condensed tannins were extracted from four sainfoin accessions: Rees ‘A’, CPI63763, Cotswold Common and CPI63767. Gas production (GP) was measured using a fully automated GP apparatus with CH4 measured at distinct time points. Condensed tannins differed substantially in terms of polymer size and varied from 13 (Rees ‘A’) to 73 (CPI63767) mean degree of polymerization, but had relatively similar characteristics in terms of CT content, procyanidin: prodelphinidin (PC: PD) and cis:trans ratios. Compared to control, addition of CT from CPI63767 and CPI63763 at 80 and 120 g CT/kg of substrate DM reduced CH4 by 43% and 65%, and by 23% and 57%, respectively, after 24-h incubation. Similarly, CT from Rees ‘A’ and Cotswold Common reduced CH4 by 26% and 46%, and by 28% and 46% respectively. Addition of increasing level of CT linearly reduced the maximum rates of GP and CH4 production, and the estimated in vitro organic matter digestibility. There was a negative linear and quadratic (p < 0.01) relation between CT concentration and total volatile fatty acid (VFA) production. Inclusion of 80 and 120 g CT/kg of substrate DM reduced (p < 0.001) branched-chain VFA production and acetate: propionate ratio and was lowest for CPI63767. A decrease in proteolytic activity as indirectly shown by a change in VFA composition favouring a shift towards propionate and reduction in branched-chain VFA production varied with type of CT and was highest for CPI63767. In conclusion, these results suggest that tannin polymer size is an important factor affecting in vitro CH4 production which may be linked to the CT interaction with dietary substrate or microbial cells.

Metrics for linking emissions of gases and aerosols to global precipitation changes

Recent advances in understanding have made it possible to relate global precipitation changes directly to emissions of particular gases and aerosols that influence climate. Using these advances, new indices are developed here called the Global Precipitation-change Potential for pulse (GPP_P) and sustained (GPP_S) emissions, which measure the precipitation change per unit mass of emissions. The GPP can be used as a metric to compare the effects of different emissions. This is akin to the global warming potential (GWP) and the global temperature-change potential (GTP) which are used to place emissions on a common scale. Hence the GPP provides an additional perspective of the relative or absolute effects of emissions. It is however recognised that precipitation changes are predicted to be highly variable in size and sign between different regions and this limits the usefulness of a purely global metric. The GPP_P and GPP_S formulation consists of two terms, one dependent on the surface temperature change and the other dependent on the atmospheric component of the radiative forcing. For some forcing agents, and notably for CO2, these two terms oppose each other – as the forcing and temperature perturbations have different timescales, even the sign of the absolute GPP_P and GPP_S varies with time, and the opposing terms can make values sensitive to uncertainties in input parameters. This makes the choice of CO2 as a reference gas problematic, especially for the GPP_S at time horizons less than about 60 years. In addition, few studies have presented results for the surface/atmosphere partitioning of different forcings, leading to more uncertainty in quantifying the GPP than the GWP or GTP. Values of the GPP_P and GPP_S for five long- and short-lived forcing agents (CO2, CH4, N2O, sulphate and black carbon – BC) are presented, using illustrative values of required parameters. The resulting precipitation changes are given as the change at a specific time horizon (and hence they are end-point metrics) but it is noted that the GPPS can also be interpreted as the time-integrated effect of a pulse emission. Using CO2 as a references gas, the GPP_P and GPP_S for the non-CO2 species are larger than the corresponding GTP values. For BC emissions, the atmospheric forcing is sufficiently strong that the GPP_S is opposite in sign to the GTP_S. The sensitivity of these values to a number of input parameters is explored. The GPP can also be used to evaluate the contribution of different emissions to precipitation change during or after a period of emissions. As an illustration, the precipitation changes resulting from emissions in 2008 (using the GPP_P) and emissions sustained at 2008 levels (using the GPP_S) are presented. These indicate that for periods of 20 years (after the 2008 emissions) and 50 years (for sustained emissions at 2008 levels) methane is the dominant driver of positive precipitation changes due to those emissions. For sustained emissions, the sum of the effect of the five species included here does not become positive until after 50 years, by which time the global surface temperature increase exceeds 1 K.

Utilization of organic nitrogen by ectomycorrhizal fungi (Hebeloma spp.) of arctic and temperate origin

Arctic and temperate strains of Hebeloma spp. were grown in axenic culture on glutamic acid, alanine, lysine and NH4+ as sole sources of nitrogen (N), with excess carbon (C) or deficient C (supplied as glucose). Their ability to utilize seed protein as a natural N source was also assessed. All strains tested had the capacity to assimilate amino acids and generally utilized alanine and glutamic acid more readily than NH4+. Some strains were able to utilize amino C when starved of glucose C, and could mineralize amino-N to NH3-N. Arctic strains, in particular, appeared to be pre-adapted to the utilization of seed protein N and glutamic acid N, which is often liberated in high concentrations after soil freezing. The results are discussed in relation to their possible ecological importance.

Design, implementation and interpretation of in vitro batchculture experiments to assess enteric methane mitigation in ruminants—a review

In vitro fermentation techniques (IVFT) have been widely used to evaluate the nutritivevalue of feeds for ruminants and in the last decade to assess the effect of different nutritionalstrategies on methane (CH4) production. However, many technical factors may influencethe results obtained. The present review has been prepared by the ‘Global Network’ FACCE-JPI international research consortium to provide a critical evaluation of the main factorsthat need to be considered when designing, conducting and interpreting IVFT experimentsthat investigate nutritional strategies to mitigate CH4emission from ruminants. Given theincreasing and wide-scale use of IVFT, there is a need to critically review reports in the lit-erature and establish what criteria are essential to the establishment and implementationof in vitro techniques. Key aspects considered include: i) donor animal species and numberof animal used, ii) diet fed to donor animals, iii) collection and processing of rumen fluidas inoculum, iv) choice of substrate and incubation buffer, v) incubation procedures andCH4measurements, vi) headspace gas composition and vii) comparability of in vitro andin vivo measurements. Based on an evaluation of experimental evidence, a set of techni-cal recommendations are presented to harmonize IVFT for feed evaluation, assessment ofrumen function and CH4production.

Fast and slow precipitation responses to individual climate forcers: a PDRMIP multi-model study

Precipitation is expected to respond differently to various drivers of anthropogenic climate change. We present the first results from the Precipitation Driver and Response Model Intercomparison Project (PDRMIP), where nine global climate models have perturbed CO2, CH4, black carbon, sulfate, and solar insolation. We divide the resulting changes to global mean and regional precipitation into fast responses that scale with changes in atmospheric absorption and slow responses scaling with surface temperature change. While the overall features are broadly similar between models, we find significant regional intermodel variability, especially over land. Black carbon stands out as a component that may cause significant model diversity in predicted precipitation change. Processes linked to atmospheric absorption are less consistently modeled than those linked to top-of-atmosphere radiative forcing. We identify a number of land regions where the model ensemble consistently predicts that fast precipitation responses to climate perturbations dominate over the slow, temperature-driven responses.