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Orwin K.H.,Lancaster University | Kirschbaum M.U.F.,Landcare Research | Kirschbaum M.U.F.,New Zealand Agricultural Greenhouse Gas Research Center | St John M.G.,Landcare Research | Dickie I.A.,Landcare Research
Ecology Letters

Understanding the factors that drive soil carbon (C) accumulation is of fundamental importance given their potential to mitigate climate change. Much research has focused on the relationship between plant traits and C sequestration, but no studies to date have quantitatively considered traits of their mycorrhizal symbionts. Here, we use a modelling approach to assess the contribution of an important mycorrhizal fungal trait, organic nutrient uptake, to soil C accumulation. We show that organic nutrient uptake can significantly increase soil C storage, and that it has a greater effect under nutrient-limited conditions. The main mechanism behind this was an increase in plant C fixation and subsequent increased C inputs to soil through mycorrhizal fungi. Reduced decomposition due to increased nutrient limitation of saprotrophs also played a role. Our results indicate that direct uptake of nutrients from organic pools by mycorrhizal fungi could have a significant effect on ecosystem C cycling and storage. © 2011 Blackwell Publishing Ltd/CNRS. Source

Reisinger A.,New Zealand Agricultural Greenhouse Gas Research Center | Meinshausen M.,Potsdam Institute for Climate Impact Research | Manning M.,Victoria University of Wellington
Environmental Research Letters

Global warming potentials (GWPs) are the metrics currently used to compare emissions of different greenhouse gases under the United Nations Framework Convention on Climate Change. Future changes in greenhouse gas concentrations will alter GWPs because the radiative efficiencies of marginal changes in CO2, CH4 and N2O depend on their background concentrations, the removal of CO2 is influenced by climate-carbon cycle feedbacks, and atmospheric residence times of CH4 and N 2O also depend on ambient temperature and other environmental changes. We calculated the currently foreseeable future changes in the absolute GWP of CO2, which acts as the denominator for the calculation of all GWPs, and specifically the GWPs of CH4 and N2O, along four representative concentration pathways (RCPs) up to the year 2100. We find that the absolute GWP of CO2 decreases under all RCPs, although for longer time horizons this decrease is smaller than for short time horizons due to increased climate-carbon cycle feedbacks. The 100-year GWP of CH4 would increase up to 20% under the lowest RCP by 2100 but would decrease by up to 10% by mid-century under the highest RCP. The 100-year GWP of N2O would increase by more than 30% by 2100 under the highest RCP but would vary by less than 10% under other scenarios. These changes are not negligible but are mostly smaller than the changes that would result from choosing a different time horizon for GWPs, or from choosing altogether different metrics for comparing greenhouse gas emissions, such as global temperature change potentials. © 2011 IOP Publishing Ltd. Source

Joos F.,University of Bern | Roth R.,University of Bern | Fuglestvedt J.S.,CICERO Center for International Climate and Environmental Research | Peters G.P.,CICERO Center for International Climate and Environmental Research | And 27 more authors.
Atmospheric Chemistry and Physics

The responses of carbon dioxide (CO2) and other climate variables to an emission pulse of CO2 into the atmosphere are often used to compute the Global Warming Potential (GWP) and Global Temperature change Potential (GTP), to characterize the response timescales of Earth System models, and to build reduced-form models. In this carbon cycle-climate model intercomparison project, which spans the full model hierarchy, we quantify responses to emission pulses of different magnitudes injected under different conditions. The CO2 response shows the known rapid decline in the first few decades followed by a millennium-scale tail. For a 100 Gt-C emission pulse added to a constant CO2 concentration of 389 ppm, 25 ± 9 % is still found in the atmosphere after 1000 yr; the ocean has absorbed 59 ± 12 % and the land the remainder (16 ± 14 %). The response in global mean surface air temperature is an increase by 0.20 ± 0.12°C within the first twenty years; thereafter and until year 1000, temperature decreases only slightly, whereas ocean heat content and sea level continue to rise. Our best estimate for the Absolute Global Warming Potential, given by the time-integrated response in CO2 at year 100 multiplied by its radiative efficiency, is 92.5 × 10-15 yr W m-2 per kg-CO2. This value very likely (5 to 95 % confidence) lies within the range of (68 to 117) × 10-15 yr W m-2 per kg-CO2. Estimates for time-integrated response in CO2 published in the IPCC First, Second, and Fourth Assessment and our multi-model best estimate all agree within 15% during the first 100 yr. The integrated CO2 response, normalized by the pulse size, is lower for pre-industrial conditions, compared to present day, and lower for smaller pulses than larger pulses. In contrast, the response in temperature, sea level and ocean heat content is less sensitive to these choices. Although, choices in pulse size, background concentration, and model lead to uncertainties, the most important and subjective choice to determine AGWP of CO2 and GWP is the time horizon. © Author(s) 2013. Source

Clark H.,New Zealand Agricultural Greenhouse Gas Research Center | Kelliher F.,Agresearch Ltd. | Pinares-Patino C.,Agresearch Ltd.
Asian-Australasian Journal of Animal Sciences

Almost half of New Zealand's greenhouse gas emissions arise from agriculture and enteric methane (CH4) emissions arising from ruminant animals constitute 30% of total CO2-e emissions. Enteric CH4 emissions have increased by 9% since 1990. Extensive research has been undertaken to develop reliable methods for measuring enteric CH4 emissions. New Zealand studies using the SF6 tracer technique suggest that on average this technique yields similar values to the 'gold' standard of calorimetry, but with a larger variance. National inventory estimates based on results obtained using the SF6 technique will therefore overestimate the uncertainty. Mitigating emissions can be achieved by changing feed type but there are practical and cost barriers to the use of alternative feeds. Forages containing condensed tannins do reduce emissions but are agronomically inferior to the forages currently used. Rumen additives have shown some success in-vitro but results from in-vivo trials with both monensin and fumaric acid have been disappointing. The development of methods for directly manipulating rumen microorganisms are at an early stage and work to develop vaccines that can inhibit methanogenesis has yielded mixed results. The successful identification of sheep with contrasting CH4 yields raises the possibility that, in the long term, a breeding approach to CH4 mitigation is feasible. Source

Clark H.,New Zealand Agricultural Greenhouse Gas Research Center

Concentrations of methane (CH4) in the atmosphere have almost doubled since the mid 1700s, and it is estimated that ∼30% of the global warming experienced by the planet in the last century and a half can be attributed to CH4. Between 25% and 40% of anthropogenic CH4, emissions are estimated to arise from livestock farming. Mitigating absolute emissions from livestock is extremely challenging technically and is made more difficult because of the need to increase food production to meet the demands of a burgeoning world population. Opportunities for manipulating the diet of intensively managed ruminant to reduce absolute CH4 exist, but in grazing livestock the opportunities are constrained practically and economically. Mitigating emissions per unit of product is more tractable, especially in the short term. Although the formation of CH4 is an anaerobic microbiological process, the host animal does seem to exert an influence, as animals differ in the quantity of CH4 they emit when fed the same diet. The reasons for this are not yet clear, but evidence is accumulating that these differences are consistent and have a genetic basis. Exploiting these between animal differences by animal breeding is an attractive mitigation option as it is potentially applicable to all animals and is open to continuous improvement. However, identifying the desired phenotype poses severe practical constraints. Vaccinating the host animal to produce antibodies that can modulate the activities of the organisms responsible for CH4 formation also presents a novel mitigation option. © 2011 The Animal Consortium. Source

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