Competing uses of biomass for energy and chemicals: implications for long‐term global CO2 mitigation potential

Biomass is considered a low carbon source for various energy or chemical options. This paper assesses it's different possible uses, the competition between these uses, and the implications for long‐term global energy demand and energy system emissions. A scenario analysis is performed using the TIMER energy system model. Under baseline conditions, 170 EJ yr^?1 of secondary bioenergy is consumed in 2100 (approximately 18% of total secondary energy demand), used primarily in the transport, buildings and nonenergy (chemical production) sectors. This leads to a reduction of 9% of CO₂ emissions compared to a counterfactual scenario where no bioenergy is used. Bioenergy can contribute up to 40% reduction in emissions at carbon taxes greater than 500/tC. As higher CO₂ taxes are applied, bioenergy is increasingly diverted towards electricity generation. Results are more sensitive to assumptions about resource availability than technological parameters. To estimate the effectiveness of bioenergy in specific sectors, experiments are performed in which bioenergy is only allowed in one sector at a time. The results show that cross‐sectoral leakage and emissions from biomass conversion limit the total emission reduction possible in each sector. In terms of reducing emissions per unit of bioenergy use, we show that the use of bioelectricity is the most effective, especially when used with carbon capture and storage. However, this technology only penetrates at a high carbon price (>100/tC) and competition with transport fuels may limit its adoption.     

Carbon and Water Footprints and Energy Use of Greenhouse Tomato Production in Northern Italy

This study reports on the carbon, water, and energy footprints of tomatoes grown in a greenhouse in Northern Italy and two possible future variations of heating and carbon dioxide (CO₂) fertilization on the current setup. The heat supply in place, consisting of natural gas (NG) and canola oil combustion, is compared to cogeneration and incineration of municipal solid waste for heating and CO₂ from industrial exhaust for fertilization. As a benchmark, the current system is also compared to a conventional system, in which heat is delivered solely based on NG. Each kilogram (kg) of fresh tomatoes (“Cuore di Bue” variety) produced in the current greenhouse emits 2.28 kg CO₂ equivalents (eq) and uses 95.5 megajoules (MJ) eq energy and 122 liters (L) of water. Relative to the system in place, the carbon footprint (CF) is 57.5% and 18% higher with conventional NG heating and cogeneration and is 40% lower with waste valorization. Further, 33%, 55%, and 63% less energy and 9%, 96%, and 14% less water are used in the conventional, cogeneration, and waste valorization scenarios, respectively. This confirms that there are multiple strategies to reduce the impact of the tomato production under consideration.     

Distributions of carbon in calcareous soils under different land uses in western Iran

Concentrations of Natural stable and unstable carbon in ecosystems have been used extensively to help to understand a wide range of soil processes and functions. This study was conducted to explore the effects of land use changes on different carbon fractions (F₁, F₂, F₃ and F₄), permanganate oxidizable carbon (POXC), soil organic carbon (SOC) and total organic carbon (TOC) associated with soils in calcareous soils of western Iran. Four popular land uses in the selected site including natural forest, range land, dryland farming and irrigated farming systems were employed as the basis of soil sampling. The results showed a strong relationship between land use conversion and SOC stocks changes. The greatest mean values for carbon content and the least mean values of CaCO₃ in bulk topsoil (0–15 cm) in the forest land were observed. Dryland farming had the least both active and passive pools of C in comparison with the other land uses. The positive and significant correlations was observed between SOC, Total C and POXC contents and different C fractions. Taking C and POXC pools into account, a more definitive picture of the soil C is obtained than when only total C is measured. The influence of land use changes on overall soil carbon stocks could be helpful for making management decision for farmers and policy makers in the future, for enhancing the potential of C sequestration in western Iran.     

Accounting for Algae

Interest and research in the use of algae for energy is growing but an analysis of the different methods for the accounting for the carbon dioxide (CO ₂) emissions that result, is lacking. In this article, four accounting systems are evaluated for their completeness, simplicity, sectoral accuracy, and scale‐independence. Two options under the Kyoto Protocol (KP), a value‐chain (end‐user responsibility) approach, and Point of Uptake and Release (POUR) are evaluated. Algal material is used in biofuels, animal feeds, human foods, and food supplements, and a range of products such as paints, cosmetics, and plastics. There are also proposals for using algae as a soil amendment. This variety of uses for algal material together with the fact that it will probably contain carbon of fossil origin presents accounting challenges and reveals inconsistencies that have lain in the KPs treatment of biomass emissions. Furthermore, a key conclusion of the article is that neither proposed KP accounting approach for algae leads to correct accounting of emissions for all uses. Both value chain and POUR approaches more correctly and consistently account for algal emissions across uses. POUR offers the potential to provide comprehensive, consistent emission accounting across all uses of biomass, which represents a major step forward in accounting for CO ₂ emissions due to use of biomass.     

Selective Etching of Nitrogen‐Doped Carbon by Steam for Enhanced Electrochemical CO2 Reduction

Nitrogen‐doped carbon structures have recently been demonstrated as a promising candidate for electrocatalytic CO₂ reduction, while in the meantime the pyridinic and graphitic nitrogen atoms also present high activities for electroreduction of water. Here, an etching strategy that uses hot water steam to preferentially bind to pyridinic and graphitic nitrogen atoms and subsequently etch them in carbon frameworks is reported. As a result, pyrrolic nitrogen atoms with low water affinity are retained after the steam etching, with a much increased level of among all nitrogen species from 22.1 to 55.9%. The steam‐etched nitrogen‐doped carbon catalyst enables excellent electrocatalytic CO₂ reduction performance but low hydrogen evolution reaction activity, suggesting a new approach for tuning electrocatalyst activity.     

Physiological and ecological controls on carbon sequestering in terrestrial ecosystems

Carbon cycling processes in ecosystems are generally believed to be well understood. Carbon, hydrogen, oxygen and other essential elements are chemically converted from inorganic to organic compounds primarily in the process of photosynthesis. Secondary metabolic processes cycle carbon in and among organisms and carbon is ultimately released back to the environment as CO₂ by respiratory processes. Unfortunately, our understanding of this cycle was determined under the assumption that the primary inorganic form of C (CO₂ in the atmosphere) was relatively constant. With the emerging concensus that atmospheric carbon concentration is increasing, we must now reassess our understanding of the carbon cycle. How will plants, animals and decomposers respond to a doubling of carbon supply? Will biological productivity be accelerated? If plant productivity increases will a predictable percentage of the increase be accumulated as increased standing crop? Or, is it possible that doubling the availability of CO₂ will increase metabolic activity at all trophic levels resulting in no net increase in system standing crop? The purpose of this paper is to review evidence for physiological and growth responses of plants to carbon dioxide enhancement. Essentially no research has been completed on the ecological aspects of these questions. From this review, I conclude that accurate predictions of future ecosystem responses to increasing atmospheric carbon dioxide concentration are not possible without additional understanding of physiological and ecological mechanisms.     

帽儿山地区不同土地利用方式下土壤-微生物-矿化碳氮化学计量特征

土地利用方式的变化导致土壤碳氮含量及其化学计量关系的变化,然而土壤微生物化学计量及其驱动的碳氮矿化过程如何响应这种变化仍不明确。以帽儿山地区天然落叶阔叶林、人工红松林、草地和农田4种不同土地利用类型为对象,测定其土壤有机碳(C_(soil))、全氮(N_(soil))、微生物生物量碳和氮(C_(mic)和N_(mic))、土壤碳和氮矿化速率(C_(min)和N_(min)),旨在比较不同土地利用方式对土壤、微生物碳氮化学计量特征及矿化速率的影响,探索土壤-微生物-矿化之间碳氮化学计量特征的相关性,揭示微生物对土壤碳氮化学计量变化的响应和调控机制。结果显示:C_(soil)、N_(soil)、C_(mic)、N_(mic)和C_(min)均呈现天然落叶阔叶林人工红松林草地农田,而天然落叶阔叶林和草地的N_(min)显著高于人工红松林和农田。土地利用方式显著影响土壤和微生物碳氮比(C∶N_(soil)和C∶N_(mic)),均呈现农田最高。不同土地利用方式的数据综合分析发现:碳氮矿化速率比与C∶N_(mic)呈负相关,而和微生物与土壤碳氮化学计量不平衡性(C∶N_(imb))显著正相关。单位微生物生物量的碳矿化速率(qCO_2)随着C∶N_(mic)的增加而降低,而单位微生物生物量的氮矿化速率(qAN)随着C∶N_(mic)的增加而增加。C∶N_(imb)与qCO_2正相关,与qAN负相关。以上结果表明,微生物会通过改变自身碳氮化学计量、调整碳氮之间相对矿化速率,以适应土地利用变化导致的土壤碳氮及其化学计量的变异性,以满足自身生长和代谢的碳氮需求平衡。     

The flux of carbon from rivers: the case for flux from England and Wales

This study uses the extensive monitoring datasets of the Environment Agency of England and Wales to calculate the flux of dissolved organic carbon (DOC); particulate organic carbon (POC); and excess dissolved CO₂ through English and Welsh rivers. The innovation of this study’s approach is to account for the losses of carbon within the fluvial system as well as fluxes at the catchment outlet. In order to make this assessment this study considers: the biochemical oxygen demand (BOD) as a measure of the degradation of DOC; and the dissolved CO₂ concentration of groundwater as calculated and apportioned into surface waters on the basis of Ca concentrations. The study shows that the best estimate of carbon export, via rivers, from England and Wales is 10.34 Mg C/km²/year, with 4.19 Mg C/km²/year of this going to the atmosphere. The mapping of the carbon export shows that there are regional hotspots of carbon export and in a small number of cases rivers could be net sinks of carbon due to their low dissolved CO₂ content relative to the atmosphere. The flux calculated by this approach is probably still an underestimate of the carbon flux through fluvial systems but the scale of the export is greater than that previously reported and there is evidence that the fluvial flux of carbon is increasing on a decadal scale.     

An improved hexagon open‐top chamber system for stable diurnal and nocturnal warming and atmospheric carbon dioxide enrichment

The use of solar passive hexagonal open‐top chambers (POTCs) is a viable method for experimentally manipulating daytime air temperatures in low‐stature plant communities at high latitudes. Here we describe a new hexagon POTC‐based system that uses thermal inertia to increase overnight temperatures and variable chamber height to reduce overheating in summer. Field data collected in tall temperate grasslands show that the presence of thermal mass raised minimum and mean nighttime air temperatures by up to 1.5 °C while lowering chamber height, along with thermal mass, limited the development of extreme daytime chamber temperatures in summer. We also demonstrate that, by using a simple, inexpensive twin carbon dioxide (CO₂) injection system regulated by an infrared gas monitor, it is possible to generate targeted and stable atmospheric CO₂ enrichment within these chambers. These innovations significantly improve the conventional hexagon POTC design and represent a low‐cost method for assessing the effects of warming and CO₂ enrichment on low‐stature vegetation in low latitude environments.     

岩溶区不同土地利用方式下土壤CO2排放模拟研究

土地利用变化作为全球气候变化研究的重要内容之一,对土壤CO₂的排放具有重要影响。岩溶区石漠化治理过程中植被恢复伴随着土地利用方式的转变,其对土壤CO₂排放的影响有待进一步研究。基于控制性实验,以土壤、岩溶含水介质初始条件相同,仅土地利用方式不同的贵州普定沙湾模拟试验场为研究对象,通过1年的土壤CO₂浓度和通量数据,研究岩溶区不同土地利用方式下土壤CO₂的排放规律及其影响因素。结果表明：(1)土壤CO₂的浓度和通量具有明显的季节变化规律,不同季节下的土壤CO₂通量呈现昼夜变化规律,温度和降雨影响着土壤CO₂的排放,前者可促进排放量,后者可抑制排放量,且不同土地利用方式受影响的程度不同;(2)耕作活动也会影响土壤CO₂的排放,耕作使得土壤变得松散,加上岩溶区下伏基岩的溶蚀作用,增加了土壤CO₂向含水层的扩散,导致春季耕地表现为负通量;(3)不同土地利用方式下土壤CO₂的年排...     

Nitrogen fixation in lichens is important for improved rock weathering

It is known that cyanobacteria in cyanolichens fix nitrogen for their nutrition. However, specific uses of the fixed nitrogen have not been examined. The present study shows experimentally that a mutualistic interaction between a heterotrophic N₂ fixer and lichen fungi in the presence of a carbon source can contribute to enhanced release of organic acids, leading to improved solubilization of the mineral substrate. Three lichen fungi were isolated fromXanthoparmelia mexicana, a foliose lichen, and they were cultured separately or with a heterotrophic N₂ fixer in nutrient broth media in the presence of a mineral substrate. Cells of the N₂-fixing bacteria attached to the mycelial mats of all fungi, forming biofilms. All biofilms showed higher solubilizations of the substrate than cultures of their fungi alone. This finding has bearing on the significance of the origin and existence of N₂-fixing activity in the evolution of lichen symbiosis. Further, our results may explain why there are N₂-fixing photobionts even in the presence of non-fixing photobionts (green algae) in some remarkable lichens such asPlacopsis gelida. Our study sheds doubt on the idea that the establishment of terrestrial eukaryotes was possible only through the association between a fungus and a phototroph.     

Isolation and Characterization of Strains CVO and FWKO B, Two Novel Nitrate-Reducing, Sulfide-Oxidizing Bacteria Isolated from Oil Field Brine

Bacterial strains CVO and FWKO B were isolated from produced brine at the Coleville oil field in Saskatchewan, Canada. Both strains are obligate chemolithotrophs, with hydrogen, formate, and sulfide serving as the only known energy sources for FWKO B, whereas sulfide and elemental sulfur are the only known electron donors for CVO. Neither strain uses thiosulfate as an energy source. Both strains are microaerophiles (1% O₂). In addition, CVO grows by denitrification of nitrate or nitrite whereas FWKO B reduces nitrate only to nitrite. Elemental sulfur is the sole product of sulfide oxidation by FWKO B, while CVO produces either elemental sulfur or sulfate, depending on the initial concentration of sulfide. Both strains are capable of growth under strictly autotrophic conditions, but CVO uses acetate as well as CO₂ as its sole carbon source. Neither strain reduces sulfate; however, FWKO B reduces sulfur and displays chemolithoautotrophic growth in the presence of elemental sulfur, hydrogen, and CO₂. Both strains grow at temperatures between 5 and 40°C. CVO is capable of growth at NaCl concentrations as high as 7%. The present 16s rRNA analysis suggests that both strains are members of the epsilon subdivision of the division Proteobacteria, with CVO most closely related to Thiomicrospira denitrifcans and FWKO B most closely related to members of the genus Arcobacter. The isolation of these two novel chemolithotrophic sulfur bacteria from oil field brine suggests the presence of a subterranean sulfur cycle driven entirely by hydrogen, carbon dioxide, and nitrate.     

Influence of rhizodeposition under elevated CO2 on plant nutrition and soil organic matter

Atmospheric CO₂ concentrations can influence ecosystem carbon storage through net primary production (NPP), soil carbon storage, or both. In assessing the potential for carbon storage in terrestrial ecosystems under elevated CO₂, both NPP and processing of soil organic matter (SOM), as well as the multiple links between them, must be examined. Within this context, both the quantity and quality of carbon flux from roots to soil are important, since roots produce specialized compounds that enhance nutrient acquisition (affecting NPP), and since the flux of organic compounds from roots to soil fuels soil microbial activity (affecting processing of SOM).From the perspective of root physiology, a technique is described which uses genetically engineered bacteria to detect the distribution and amount of flux of particular compounds from single roots to non-sterile soils. Other experiments from several labs are noted which explore effects of elevated CO₂ on root acid phosphatase, phosphomonoesterase, and citrate production, all associated with phosphorus nutrition. From a soil perspective, effects of elevated CO₂ on the processing of SOM developed under a C4 grassland but planted with C3 California grassland species were examined under low (unamended) and high (amended with 20 g m^–2 NPK) nutrients; measurements of soil atmosphere 13C combined with soil respiration rates show that during vegetative growth in February, elevated CO₂ decreased respiration of carbon from C4 SOM in high nutrient soils but not in unamended soils.This emphasis on the impacts of carbon loss from roots on both NPP and SOM processing will be essential to understanding terrestrial ecosystem carbon storage under changing atmospheric CO₂ concentrations.Abbreviations SOM soil organic matter - NPP net primary productivity - NEP net ecosystem productivity - PNPP p-nitrophenyl phosphate     

Using ecosystem CO2 measurements to estimate the timing and magnitude of greenhouse gas mitigation potential of forest bioenergy

Forest bioenergy opportunities may be hindered by a long greenhouse gas (GHG) payback time. Estimating this payback time requires the quantification of forest‐atmosphere carbon exchanges, usually through process‐based simulation models. Such models are prone to large uncertainties, especially over long‐term carbon fluxes from dead organic matter pools. We propose the use of whole ecosystem field‐measured CO₂ exchanges obtained from eddy covariance flux towers to assess the GHG mitigation potential of forest biomass projects as a way to implicitly integrate all field‐level CO₂ fluxes and the inter‐annual variability in these fluxes. As an example, we perform the evaluation of a theoretical bioenergy project that uses tree stems as bioenergy feedstock and include multi‐year measurements of net ecosystem exchange (NEE) from forest harvest chronosequences in the boreal forest of Canada to estimate the time dynamics of ecosystem CO₂ exchanges following harvesting. Results from this approach are consistent with previous results using process‐based models and suggest a multi‐decadal payback time for our project. The time for atmospheric carbon debt repayment of bioenergy projects is highly dependent on ecosystem‐level CO₂ exchanges. The use of empirical NEE measurements may provide a direct evaluation of, or at least constraints on, the GHG mitigation potential of forest bioenergy projects.     

基于碳排放约束的北京市社区生态效率评价

在“双碳目标”的背景下,社区作为生态文明建设的基本单元,其碳排放核算及生态效率评估尤为重要。基于家庭消费视角,采用碳排放系数法和消费者生活方式法核算社区居民碳排放,并运用超效率DEA模型评估社区生态效率,最后通过计量分析识别生态效率影响因素。研究结果显示：(1)社区居民人均碳排放的评估结果呈现出商品房社区(528.85kgCO₂/月)>单位社区(475.66kgCO₂/月)>传统社区(368.33kgCO₂/月)的关系;(2)生态效率的评估结果呈现出传统社区(111.04%)>商品房社区(108.78%)>单位社区(105.70%)的关系;(3)社区管理工作参与意愿、家庭光照条件会对社区生态效率产生积极影响;此外,年龄结构(中青年人口占比)对商品房社区的生态效率有消极影响,受教育程度的提升则会提高生态效率。进一步提出针对三类社区特点的转型发展策略,为全国不同类型社区生态转型和绿色低碳发展提供参考范式和决策支持。     

Coassimilation of Organic Substrates via the Autotrophic 3-Hydroxypropionate Bi-Cycle in Chloroflexus aurantiacus

Chloroflexus aurantiacus is a facultative autotrophic green nonsulfur bacterium that grows phototrophically in thermal springs and forms microbial mats with cyanobacteria. Cyanobacteria produce glycolate during the day (photorespiration) and excrete fermentation products at night. C. aurantiacus uses the 3-hydroxypropionate bi-cycle for autotrophic carbon fixation. This pathway was thought to be also suited for the coassimilation of various organic substrates such as glycolate, acetate, propionate, 3-hydroxypropionate, lactate, butyrate, or succinate. To test this possibility, we added these compounds at a 5 mM concentration to autotrophically pregrown cells. Although the provided amounts of H₂ and CO₂ allowed continuing photoautotrophic growth, cells immediately consumed most substrates at rates equaling the rate of autotrophic carbon fixation. Using [¹⁴C]acetate, half of the labeled organic carbon was incorporated into cell mass. Our data suggest that C. aurantiacus uses the 3-hydroxypropionate bi-cycle, together with the glyoxylate cycle, to channel organic substrates into the central carbon metabolism. Enzyme activities of the 3-hydroxypropionate bi-cycle were marginally affected when cells were grown heterotrophically with such organic substrates. The 3-hydroxypropionate bi-cycle in Chloroflexi is unique and was likely fostered in an environment in which traces of organic compounds can be coassimilated. Other bacteria living under oligotrophic conditions acquired genes of a rudimentary 3-hydroxypropionate bi-cycle, possibly for the same purpose. Examples are Chloroherpeton thalassium, Erythrobacter sp. strain NAP-1, Nitrococcus mobilis, and marine gammaproteobacteria of the OM60/NOR5 clade such as Congregibacter litoralis.     

Evaluating soil biochemical/microbial indices as ecological indicators of different land use/cover in northern Iran

The objective of the study was to examine changes in microbial parameters have been used to monitor changes in soil quality under different land uses in north of Iran. The microbial parameters included microbial respiration (MR), substrate induced respiration (SIR), carbon availability index (CAI), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), ratio of MBC/MBN, metabolic quotient (qCO₂) and microbial ratio were determined under different land use/cover, i.e. virgin natural forest (VNF), degraded natural forest (DNF), alder plantation (AP), sequoia plantation (SP), improved fallow (IF) and home garden (HG) areas in northern Iran. Five composed samples per land use/cover were taken from the top 10 cm of the soil. MR and SIR (0.45 and 1.66 mg CO₂-C g^?1 day^?1, respectively) were found to be significantly higher under AP land uses than in the other areas. CAI did not differ for the land uses; MBC (591 and 590 mg kg^?1, respectively) had higher significantly under SP and VNF land uses than in the other areas. MBN (64.25 and 62.33, respectively mg kg^?1) was significantly higher in AP and VNF land uses, ratio of MBC/MBN (17.02) was higher in SP land use than other areas, HG had significantly higher qCO₂ (0.0012 μg CO₂-C mg^?1 MBC day^?1) and finally microbial ratio was significantly higher under IF (599.16) in comparison with HG > AP ≈ DNF > VNF > SP areas. Overall, our results indicate that AP land use (Alnus subcordata C. A. Mey.) increase of soil quality and alder plantation is suitable for rehabilitation of degraded natural forests.     

Experimental warming increases CO2 saturation in a shallow prairie pond

There is an urgent need to understand the effect of climate warming on the carbon dynamics of lakes and ponds in order to assess contributions to global carbon budgets. Currently, we are unable to predict how the exchange of carbon gases (i.e. CO₂) across the air–water boundary and organic carbon storage in the sediments will be altered with realistic warming scenarios downscaled from climatic models. Given the prevalence of shallow systems and tight atmospheric coupling, we conducted a mesocosm experiment to test the impacts of warming on CO₂ saturation in a shallow prairie pond. We outline and test three possible scenarios for the effect of warming on the CO₂ saturation of ponds, resulting in either an increase, decrease or no net effect for CO₂ saturation. We show that with approximately a two-degree (ºC) increase in average water temperature, the pCO₂ of the warmed mesocosms was nine times greater than the ambient temperature mesocosms by the end of the 5-week experiment. Changes in water colour (a measure of dissolved organic carbon) in warmed systems indicate that decomposition of organic matter in the sediments and water column was the main contributor to the increase in pCO₂ in the warmed mesocosms. Our results show that with warming, the release of CO₂ from shallow ponds to the atmosphere will increase and carbon storage in the sediments will decrease, altering the current functioning of shallow prairie ponds and influencing the contribution of ponds to the global carbon cycle.     

Significance of <Emphasis Type="Italic">Halimeda</Emphasis> bioherms to the global carbonate budget based on a geological sediment budget for the Northern Great Barrier Reef,Australia

Since the correlation between carbon dioxide (CO₂) levels and global temperatures was established in the ice core records, quantifying the components of the global carbon cycle has become a priority with a view to constraining models of the climate system. The marine carbonate budget is still not adequately constrained and the quantitative significance of the calcareous green alga Halimeda still remains particularly poorly understood. Previously, it has been suggested that Halimeda bioherms on the shelf of the Great Barrier Reef may contain a volume of carbonate equal to or greater than that contained within the shelf edge coral reefs. This study uses published datasets to test this hypothesis in the Northern Great Barrier Reef (NGBR) province. It is estimated that Halimeda bioherms on the outer shelf of the NGBR contain at least as much (and up to four times more) CaCO₃ sediment as the adjacent ribbon reef facies. Globally, if these findings are even only partially applicable, the contribution of shallow water carbonate sediments to the global carbon budget based on coral reefs alone is currently substantially underestimated.     

Taxonomical examination and characterization of a methanol-utilizing yeast

The morphological, cultural, and physiological characteristics are described of a yeast, LI70, which uses methanol as its source of energy and carbon; these characteristics have made it possible to identify the strain as Candida boidinii Ramirez. The identification was confirmed by a DNA-DNA genetic homology of 99.43% with the type strain of C. boidinii. Strain LI70 is not pathogenic.