On Photosynthesis and Organic Carbon, Carbon Dioxide, and Oxygen Flows in the Ocean

The modern concept of photosynthesis as a mechanism for utilizing the energy of solar radiation is used as the basis for assessing the scale of photosynthetic production of initial organic matter in the ocean (primary biological production), its destruction, the carbon and carbon dioxide cycles (flows) involved in this process, and the size of oil- and gas-bearing hydrocarbonaceous formations originating in sedimentary deposits.     

Leaf Phosphate Status, Photosynthesis, and Carbon Partitioning in Sugar Beet: III. Diurnal Changes in Carbon Partitioning and Carbon Export

The effect of low phosphate supply (low P) was determined on the diurnal changes in the rate of carbon export, and on the contents of starch, sucrose, glucose, and fructose 2,6-bisphosphate (F2,6BP) in leaves. Low-P effects on the activities of a number of enzymes involved in starch and sucrose metabolism were also measured. Sugar beets (Beta vulgaris L. cv. F58-554H1) were cultured hydroponically in growth chambers and the low-P treatment induced nutritionally. Low-P treatment decreased carbon export from the leaf much more than it decreased photosynthesis. At growth chamber photon flux density, low P decreased carbon export by 34% in light; in darkness, export rates fell but more so in the control so that the average rate in darkness was higher in low-P leaves. Low P increased starch, sucrose, and glucose contents per leaf area, and decreased F2, 6BP. The total extractable activities of enzymes involved in starch and sucrose synthesis were increased markedly by low P, e.g. adenosine 5-diphosphoglucose pyrophosphorylase, cytoplasmic fructose-1,6-bisphosphatase, uridine 5-diphosphoglucose pyrophosphorylase, and sucrose-phosphate synthase. The activities of some enzymes involved in starch and sucrose breakdown were also increased by low P. We propose that plants adapt to low-P environments by increasing the total activities of several phosphatases and by increasing the concentrations of phosphate-free carbon compounds at the expense of sugar phosphates, thereby conserving Pi. The partitioning of carbon among the various carbon pools in low-P adapted leaves appears to be determined in part by the relative capacities of the enzymes for starch and sucrose metabolism.     

Biosphere Structure, Carbon Sequestering Potential and the Atmospheric 14C Carbon Record

The behaviour of a numerical model for the global carbon cycleis eluidated by a simple analytical model for the biosphere.In the period 1980—1990 the ocean is estimated to haveabsorbed 33% of the total CO₂ emission to the atmosphere inthat same period. Net deforestation was responsible for 12—17%of this total emission rate, whereas the CO₂-fertilization effectcaused a re-absorption of 20—25%. Aggregation of the above-ground biosphere into a single poolin the model caused an oversitmation of the CO₂-fertilizationeffect. Also, the estimate of this rate increased when the fractionof carbon assumed to remain after the transformation of litterinto humus was increased, but the rate was little influencedby the model structure for soil organic carbon. A larger estimate for carbon uptake in the biosphere (Tans,Fung, and Takahashi, 1990) must be compensated by a reduceduptake in the ocean to arrive at a carbon balance. To do this,either the exchange rate between the upper mixed ocean layerand deep sea, or between ocean surface and atmosphere, shouldbe reduced. In addition, a good match to the observed time-courseof ¹⁴C carbon in the atmosphere must be preserved by the model.The ¹⁴C time-course did not remain well-matched if the atmosphere—oceansurface exchange was reduced, but it was hardly distrubed atall if the exchange rate with the deep sea was reduced. Key words: CO₂-fertilization, global carbon cycle.     

Stable Carbon Isotope Fractionation by Methanosarcina barkeri during Methanogenesis from Acetate, Methanol, or Carbon Dioxide-Hydrogen

Methanosarcina barkeri was cultured on methanol, H₂-CO₂, and acetate, and the ¹³C/¹²C ratios of the substrates and the methane produced from them were determined. The discrimination against ¹³C in methane relative to substrate decreased in the order methanol > CO₂ > acetate. The isotopic fractionation for methane derived from acetate was only one-third of that observed with methanol as the substrate. The data presented indicate that the last enzyme of methanogenesis, methylreductase, is not the primary site of isotopic discrimination during methanogenesis from methanol or CO₂. These results also support biogeochemical interpretations that gas produced in environments in which acetate is the primary methane precursor will have higher ¹³C/¹²C ratios than those from environments where other substrates predominate.     

Effects of Carbon Source, Carbon Concentration, and Chlorination on Growth Related Parameters of Heterotrophic Biofilm Bacteria

Abstract To investigate growth of heterotrophic biofilm bacteria, a model biofilm reactor was developed to simulate a drinking water distribution system. Controlled addition of three different carbon sources (amino acids, carbohydrates, and humics) at three different concentrations (500, 1,000, and 2,000 ppb carbon) in the presence and absence of chlorine were used in separate experiments. An additional experiment was run with a 1:1:2 mixture of the above carbon sources. Biofilm and effluent total and culturable cells in addition to total and dissolved organic carbon were measured in order to estimate specific growth rates (SGRs), observed yields, population densities, and bacterial carbon production rates. Bacterial carbon production rates (μg C/L day) were extremely high in the control biofilm communities (range = 295–1,738). Both growth rate and yield decreased with increasing carbon concentrations. Therefore, biofilm growth rates were zero-order with respect to the carbon concentrations used in these experiments. There was no correlation between growth rate and carbon concentration, but there was a significant negative correlation between growth rate and biofilm cell density (r=−0.637, p= 0.001 control and r=−0.57, p= 0.021 chlorinated biofilms). Growth efficiency was highest at the lowest carbon concentration (range = 12–4.5%, amino acids and humics respectively). Doubling times ranged from 2.3–15.4 days in the control biofilms and 1–12.3 days in the chlorinated biofilms. Growth rates were significantly higher in the presence of chlorine for the carbohydrates, humics, and mixed carbon sources (p= 0.004, < 0.0005, 0.013, respectively). The concept of r/K selection theory was used to explain the results with respect to specific growth rates and yields. Humic removal by the biofilm bacteria (78% and 56% for the control and chlorinated biofilms, respectively) was higher than previously reported literature values for planktonic bacteria. A number of control experiments indicated that filtration of drinking water was as effective as chlorination in controlling bacterial biofilm growth. Received: 26 March 1999; Accepted: 3 August 1999; Online Publication: 15 February 2000     

Metabolism,Gas Exchange,and Carbon Spiraling in Rivers

Ecosystem metabolism, that is, gross primary productivity (GPP) and ecosystem respiration (ER), controls organic carbon (OC) cycling in stream and river networks and is expected to vary predictably with network position. However, estimates of metabolism in small streams outnumber those from rivers such that there are limited empirical data comparing metabolism across a range of stream and river sizes. We measured metabolism in 14 rivers (discharge range 14–84 m³ s^?1) in the Western and Midwestern United States (US). We estimated GPP, ER, and gas exchange rates using a Lagrangian, 2-station oxygen model solved in a Bayesian framework. GPP ranged from 0.6–22 g O₂ m^?2 d^?1 and ER tracked GPP, suggesting that autotrophic production supports much of riverine ER in summer. Net ecosystem production, the balance between GPP and ER was 0 or greater in 4 rivers showing autotrophy on that day. River velocity and slope predicted gas exchange estimates from these 14 rivers in agreement with empirical models. Carbon turnover lengths (that is, the distance traveled before OC is mineralized to CO₂) ranged from 38 to 1190 km, with the longest turnover lengths in high-sediment, arid-land rivers. We also compared estimated turnover lengths with the relative length of the river segment between major tributaries or lakes; the mean ratio of carbon turnover length to river length was 1.6, demonstrating that rivers can mineralize much of the OC load along their length at baseflow. Carbon mineralization velocities ranged from 0.05 to 0.81 m d^?1, and were not different than measurements from small streams. Given high GPP relative to ER, combined with generally short OC spiraling lengths, rivers can be highly reactive with regard to OC cycling.     

秦岭宁陕县森林植被碳储量与碳密度特征

以秦岭南坡中段宁陕县林区2003年二类森林调查资料为基础,采用政府间气候变化委员会(IPCC)推荐使用的森林碳储量估算方法,从森林类型、林种、年龄和林分起源的角度,对该林区森林植被碳储量和碳密度进行估算。结果显示:(1)宁陕县森林植被碳储量为12.31Tg(1Tg=1×1012 g),平均碳密度为66.36Mg/hm2(1Mg=1×106 g),其各乡镇森林植被碳储量和碳密度在空间上的分布不平衡。(2)各森林类型中针叶林总碳储量为0.71Tg,平均碳密度为64.11 Mg/hm2,阔叶林总碳储量为11.61Tg,占宁陕县总碳储量的94.3%,碳密度为67.65Mg/hm2。(3)各林种中防护林碳储量最大(8.13Tg),占宁陕县总碳储量的66%,特种用途林碳密度最大(81.43Mg/hm2)。(4)不同林分起源中,天然林碳储量为12.231Tg,占宁陕县总碳储量的99.3%,人工林碳储量较小。(5)不同年龄森林中未成熟森林(包括幼龄林、中龄林和近熟林)碳储量为12.13Tg,占总碳储量的98.5%,近熟林碳密度最大(80.14Mg/hm2),幼龄林碳密度最小(39.85Mg/hm2)。研究表明,宁陕县森林具有较大的固碳能力和固碳潜力,其森林面积和蓄积是决定森林碳储量大小的重要因子,而森林碳密度的大小与森林类型、年龄组成和林分起源方式密切相关。     

广东韶关市公益林乔木层碳密度和碳储量研究

对韶关市公益林乔木层的优势树种和龄组的碳储量、碳密度和碳汇量进行分析。结果表明,韶关公益林乔木林碳储量为190.06 Tg,固碳总量优势树种以阔叶林为主,龄组以中幼林为主;平均碳密度为34.73 t·hm^–2,随着龄组增加,树种的碳密度普遍呈增加趋势;公益林乔木林碳汇量为23.90万t·a^–1,以中幼林的碳汇为主。提高阔叶林和中幼龄树种的单位面积蓄积量,是增加公益林有机碳储量和碳汇功能的主要途径。     

Carbon mitigation by the energy crop, Miscanthus

Biomass crops mitigate carbon emissions by both fossil fuel substitution and sequestration of carbon in the soil. We grew Miscanthus x giganteus for 16 years at a site in southern Ireland to (i) compare methods of propagation, (ii) compare response to fertilizer application and quantify nutrient offtakes, (iii) measure long-term annual biomass yields, (iv) estimate carbon sequestration to the soil and (v) quantify the carbon mitigation by the crop. There was no significant difference in the yield between plants established from rhizome cuttings or by micro-propagation. Annual off-takes of N and P were easily met by soil reserves, but soil K reserves were low in unfertilized plots. Potassium deficiency was associated with lower harvestable yield. Yields increased for 5 years following establishment but after 10 years showed some decline which could not be accounted for by the climate driven growth model MISCANMOD. Measured yields were normalized to estimate both autumn (at first frost) and spring harvests (15 March of the subsequent year). Average autumn and spring yields over the 15 harvest years were 13.4±1.1 and 9.0±0.7 t DW ha⁻¹ yr⁻¹ respectively. Below ground biomass in February 2002 was 20.6±4.6 t DW ha⁻¹. Miscanthus derived soil organic carbon sequestration detected by a change in ¹³C signal was 8.9±2.4 t C ha⁻¹ over 15 years. We estimate total carbon mitigation by this crop over 15 years ranged from 5.2 to 7.2 t C ha⁻¹ yr⁻¹ depending on the harvest time.     

Carbon sequestration in a high-elevation, subalpine forest

We studied net ecosystem CO₂ exchange (NEE) dynamics in a high‐elevation, subalpine forest in Colorado, USA, over a two‐year period. Annual carbon sequestration for the forest was 6.71 mol C m^?2 (80.5 g C m^?2) for the year between November 1, 1998 and October 31, 1999, and 4.80 mol C m^?2 (57.6 g C m^?2) for the year between November 1, 1999 and October 31, 2000. Despite its evergreen nature, the forest did not exhibit net CO₂ uptake during the winter, even during periods of favourable weather. The largest fraction of annual carbon sequestration occurred in the early growing‐season; during the first 30 days of both years. Reductions in the rate of carbon sequestration after the first 30 days were due to higher ecosystem respiration rates when mid‐summer moisture was adequate (as in the first year of the study) or lower mid‐day photosynthesis rates when mid‐summer moisture was not adequate (as in the second year of the study). The lower annual rate of carbon sequestration during the second year of the study was due to lower rates of CO₂ uptake during both the first 30 days of the growing season and the mid‐summer months. The reduction in CO₂ uptake during the first 30 days of the second year was due to an earlier‐than‐normal spring warm‐up, which caused snow melt during a period when air temperatures were lower and atmospheric vapour pressure deficits were higher, compared to the first 30 days of the first year. The reduction in CO₂ uptake during the mid‐summer of the second year was due to an extended drought, which was accompanied by reduced latent heat exchange and increased sensible heat exchange. Day‐to‐day variation in the daily integrated NEE during the summers of both years was high, and was correlated with frequent convective storm clouds and concomitant variation in the photosynthetic photon flux density (PPFD). Carbon sequestration rates were highest when some cloud cover was present, which tended to diffuse the photosynthetic photon flux, compared to periods with completely clear weather. The results of this study are in contrast to those of other studies that have reported increased annual NEE during years with earlier‐than‐normal spring warming. In the current study, the lower annual NEE during 2000, the year with the earlier spring warm‐up, was due to (1) coupling of the highest seasonal rates of carbon sequestration to the spring climate, rather than the summer climate as in other forest ecosystems that have been studied, and (2) delivery of snow melt water to the soil when the spring climate was cooler and the atmosphere drier than in years with a later spring warm‐up. Furthermore, the strong influence of mid‐summer precipitation on CO₂ uptake rates make it clear that water supplied by the spring snow melt is a seasonally limited resource, and summer rains are critical for sustaining high rates of annual carbon sequestration.     

Carbon footprinting,labelling and life cycle assessment

The International Journal of Life Cycle Assessment -     

Soil Carbon Stocks and Soil Carbon Quality in the Upland Portion of a Boreal Landscape,James Bay,Quebec

As part of a multidisciplinary project on carbon (C) dynamics of the ecosystems characterizing the Eastmain Region Watershed (James Bay, Quebec), the objective of this study is to compare the soil C stocks and soil organic matter quality among the main upland vegetation types in a boreal region subjected to a high fire frequency. On average, the organic layer contained twice the amount of C than the mineral soil. Closed canopy vegetation types had greater C stocks both in the mineral and in the organic layers than the other more open canopy vegetation types. Landscape features such as drainage and surficial deposit could not discriminate between vegetation types although closed vegetation types were on average found on wetter site conditions. Average soil C contents varied more than 2-fold across vegetation types. On the opposite, except for the organic layer C:N ratio, which was smaller in closed vegetation types, other measured soil organic matter properties (namely specific rate of evolved C after a long-term incubation, hydrolysis acid-resistant C as well as the rate of changes in soil heterotrophic respiration with increasing temperature (Q10)) remained within a narrow range between vegetation types. Therefore, total soil C stocks were a major determinant of both labile C and estimated summer soil heterotrophic respiration rate. The homogeneity of soil organic matter quality across the vegetation types could be attributable to the positive relationship between soil C storage and soil C fluxes observed in this landscape experiencing a high fire frequency. The low variability in soil C quality could help simplify the modelling of soil C fluxes in this environment.     

Carbon for soils,not soils for carbon

The role of soil organic carbon (SOC) sequestration as a ‘win-win’ solution to both climate change and food insecurity receives an increasing promotion. The opportunity may be too good to be missed! Yet the tremendous complexity of the two issues at stake calls for a detailed and nuanced examination of any potential solution, no matter how appealing. Here, we critically re-examine the benefits of global SOC sequestration strategies on both climate change mitigation and food production. While estimated contributions of SOC sequestration to climate change vary, almost none take SOC saturation into account. Here, we show that including saturation in estimations decreases any potential contribution of SOC sequestration to climate change mitigation by 53%–81% towards 2100. In addition, reviewing more than 21 meta-analyses, we found that observed yield effects of increasing SOC are inconsistent, ranging from negative to neutral to positive. We find that the promise of a win-win outcome is confirmed only when specific land management practices are applied under specific conditions. Therefore, we argue that the existing knowledge base does not justify the current trend to set global agendas focusing first and foremost on SOC sequestration. Away from climate-smart soils, we need a shift towards soil-smart agriculture, adaptative and adapted to each local context, and where multiple soil functions are quantified concurrently. Only such comprehensive assessments will allow synergies for land sustainability to be maximised and agronomic requirements for food security to be fulfilled. This implies moving away from global targets for SOC in agricultural soils. SOC sequestration may occur along this pathway and contribute to climate change mitigation and should be regarded as a co-benefit.     

Carbon monoxide, oxidative stress, and mitochondrial permeability pore transition

The cellular effects of carbon monoxide (CO) are produced primarily by CO binding to iron or other transition metals, which may also promote prooxidant activities of the more reactive gases, oxygen and nitric oxide. We tested the hypothesis that prooxidant effects of CO deregulate the calcium-dependent mitochondrial pore transition (MPT), which disrupts membrane potential and releases apoptogenic proteins. Rats were exposed to either CO (50 ppm) or hypobaric hypoxia (HH) for 1, 3, or 7 days, and liver mitochondria harvested to study protein expression and sensitivity to MPT by calcium and oxidants. Both exposures induced hypoxia-sensitive protein expression: hypoxia-inducible factor 1alpha (HIF-1alpha), heme oxygenase-1 (HO-1), and manganese SOD (SOD2), but SOD2 induction was greater by CO than by HH, especially at 7 days. Relative to HH, CO also caused significant early mitochondrial oxidative and nitrosative stress shown by decreases in GSH/GSSG and increases in protein 3-nitrotyrosine (3-NT) and protein mixed disulfide formation. This altered MPT sensitivity to calcium through an effect on the "S-site," causing loss of pore protection by adenine nucleotides. By 7 days, despite continued CO, nitrosative stress decreased and adenine nucleotide protection was restored to preexposure levels. This is the first evidence of functional mitochondrial pore stress caused by CO independently of its hypoxic effect, as well as a compensatory response exemplifying a mitochondrial phenotype shift. The implications are that cellular CO can activate or deactivate mitochondria for initiation of apoptosis in vivo.