Increasing stomatal conductance inresponse to rising atmospheric CO2

Background and Aims: Studies have indicated that plant stomatal conductance (gs) decreases in response to elevated atmospheric CO2, a phenomenon of significance for the global hydrological cycle. However, gs increases across certain CO2 ranges have been predicted by optimisation models. The aim of this work was to demonstrate that under certain environmental condition, gs can increase in response to elevated CO2. Methods: When using (i) an extensive, up-to-date, synthesis of gs responses in FACE experiments, (ii) in situ measurements across four biomes showing dynamic gs responses to a CO2 rise of ~50ppm (characterising the change in this greenhouse gas over the past three decades) and (iii) a photosynthesis-stomatal conductance model, it is demonstrated that gs can in some cases increase in response to increasing atmospheric CO2. Key Results: Field observations are corroborated by an extensive synthesis of gs responses in FACE experiments showing that 11.8% of gs responses under experimentally elevated CO2 are positive. They are further supported by a strong data-model fit (r2=0.607) using a stomatal optimization model applied to the field gs dataset. A parameter space identified in the Farquhar-Ball-Berry photosynthesis-stomatal conductance model confirms field observations of increasing gs under elevated CO2 in hot dry conditions. It was shown that contrary to the general assumption, positive gs responses to elevated CO2, although relatively rare, are a feature of woody taxa adapted to warm, low-humidity conditions, and that this response is also demonstrated in global simulations using the Community Land Model (CLM4). Conclusions: The results contradict the over-simplistic notion that global vegetation always responds with decreasing gs to elevated CO2, a finding that has important implications for predicting future vegetation feedbacks on the hydrological cycle at the regional level.Irish Research CouncilScience Foundation Irelan

Surface roughness noise prediction for silent aircraft experimental design SAX-40

Surface roughness noise is a potentially important contributor to airframe noise. In this paper, noise assessment due to surface roughness is performed for a conceptual Silent Aircraft design SAX-40 by means of a prediction model developed in previous theoretical work and validated experimentally. Estimates of three idealized test cases show that surface roughness could produce a significant noise level above that due to the trailing edge at high frequencies. Roughness height and roughness density are the two most significant parameters influencing surface roughness noise, with roughness height having the dominant effect. The ratio of roughness height to boundary-layer thickness is the relevant non-dimensional parameter and this decreases in the streamwise direction. The candidate surface roughness is selected for SAX-40 to meet an aggressive noise target and keep surface roughness noise at a negligible level. Copyright © 2008 by Yu Liu and Ann P. Dowling

Lifecycle greenhouse gas footprint and minimum selling price of renewable diesel and jet fuel from fermentation and advanced fermentation production technologies

Fermentation and advanced fermentation (AF) biofuel production technologies may offer a means to reduce the greenhouse gas (GHG) intensity of transportation by providing renewable drop-in alternatives to conventional middle distillate (MD) fuels, including diesel and jet fuel. To the best of our knowledge, this is the first peer-reviewed study of the environmental and economic feasibility of AF technologies. We find that the attributional lifecycle GHG footprint of AF MD from sugar cane, corn grain and switchgrass ranges from -27.0 to 19.7, 47.5 to 117.5, and 11.7 to 89.8 gCO 2e/MJMD, respectively, compared to 90.0 gCO 2e/MJMD for conventional MD. These results are most sensitive to the co-product allocation method used, the efficiency and utility requirements of feedstock-to-fuel conversion, and the co-generation technology employed. We also calculate the minimum selling price (MSP) of MD fuel produced from sugar cane, corn grain and switchgrass AF as a range from 0.61 to 2.63, 0.84 to 3.65, and 1.09 to 6.30 $per literMD, respectively, compared to the current price of conventional MD in the United States of approximately 0.80$ per literMD. The MSP results are most sensitive to feedstock-to-fuel conversion efficiency, feedstock costs, and capital costs. Finally, we demonstrate that emissions from land use change (LUC) directly attributable to the growth of biomass for AF fuel could dominate the GHG footprint of AF MD fuels. This journal is © 2014 the Partner Organisations

Halophytes for the Production of Liquid Biofuels

We discuss the potential of using halophytes as a source for producing liquid biofuels. We review the potential pathways for converting oilseeds into biodiesel and bio-derived synthetic paraffinic kerosene and presents some preliminary data on biomass composition and pretreatment of the halophyte Salicornia bigelovii. Six samples of S. bigelovii cultivated at three fertilizer levels (F1: 1 gN/m2, F2: 1.5 gN/m2 and F3: 2 gN/m2) and two salinity levels (S1: 10 ppt and S5: 50 ppt salt) were analyzed with regard to chemical composition and bioethanol potential. Chemical characterization showed that S. bigelovii contained, 16.31–55.67 g/100gTS (total solids) of carbohydrates, 5.42–16.60 g/100gTS of lignin, 27.85–66.37 g/100gTS of total extractives (including extractable ash), and 2.18–9.68 g/100gTS of structural ash, depending on the plant fraction and cultivation conditions. Enzymatic hydrolysis of the pretreated samples revealed high glucose recoveries of up to 90 % (of glucose in raw S. bigelovii) corresponding to ethanol yield of 111 kg ethanol/dry ton S. bigelovii