1965–2010年大兴安岭森林火灾碳排放的估算研究

 火干扰是森林生态系统的重要干扰因子, 是导致植被和土壤碳储量发生变化的重要原因。火干扰所排放的含碳气体对气候变化具有重要的影响。科学有效地对森林火灾所排放的碳进行计量, 对了解区域和全球的碳平衡及碳循环具有重要的意义。根据大兴安岭森林资源调查数据和1965–2010年森林火灾统计资料, 利用地理信息系统GIS (geographic information system)技术, 通过野外火烧迹地调查与室内控制环境实验相结合的方法确定各种计量参数, 从林分水平上, 采用排放因子法, 估算了大兴安岭1965–2010年46年间森林火灾所排放的碳和含碳气体量。结果表明: 大兴安岭46年间森林火灾排放的碳为2.93 × 10⁷ t, 年平均排放量为6.38 × 10⁵ t, 约占全国年均森林火灾碳排放量的5.64%; 含碳气体CO₂、CO、CH₄和非甲烷烃(NMHC)的排放量分别为1.02 × 10⁸、9.41 × 10⁶、5.41 × 10⁵和2.11 × 10⁵ t, 含碳气体CO₂、CO、CH₄和NMHC的年均排放量分别为2.22 × 10⁶、2.05 × 10⁵、1.18 × 10⁴和4.59 × 10³ t, 分别占全国年均森林火灾各含碳气体排放量的5.46%、7.56%、10.54%和4.06%; 针阔混交林燃烧效率较低, 虽然火烧面积占总过火面积的21.23%, 但排放的碳只占总排放量的7.81%, 为此提出了相应的林火管理策略。     

On-line measurement of dissolved and gaseous hydrogen sulphide in anaerobic biogas reactors

The paper presented demonstrates the calibration of a silicone membrane probe for measurement of hydrogen sulphide in liquid and gas phase. The probe is connected to a quadrupole mass spectrometer as detector. The calibration of the probe results in linear calibration functions for different liquids and the gas phase. An example of the application of the measuring device for on-line measurement is reported for an experiment where sulphide is precipitated as iron sulphide by the addition of ferrous chloride. As a consequence of the addition of ferrous chloride, the concentration of H₂S in the biogas rapidly decreases from 4.2% to 1.0% (by volume). The inhibition of the anaerobic treatment process is calculated on the basis of the reduction of dissolved total organic carbon before and during the experiment. The reduction of dissolved total organic carbon before the experiment starts is constant at 60%, rising to a maximum of 70% during the addition of FeCl₂. The difference in the conversion rate corresponds to an inhibition of about 14%. The gas production increases from 7.51 l^–1 day^–1 to 8.51 l^–1 day^–1. This inhibition observed before the addition of FeCl₂ is caused by 65 mg/l undissociated hydrogen sulphide in the liquid phase as calculated from the data obtained after precipitation of sulphide as zinc sulphide. The data show clearly that the conversion of acetic acid to methane is inhibited by dissolved H₂S. The concentration of acetic acid drops sharply from about 25 mM to 15 mM after the FeCl₂ dosage has been started. The concentration of propionic acid decreases slightly from 12 mM to 9 mM. Most of the iron introduced during the experiment is immediately precipitated. The maximum concentration of dissolved iron measured in the effluent is 93 mg/l.     

An improved equation and assay for determining the CO2/O2 specificity for Rubisco

The determination of the CO₂/O₂ specificity factor (Ω) is very important to investigate the Rubisco carbon assimilation efficiency. In this paper, it is proved that previous formulae can introduce notable errors into calculating the CO₂/O₂ specificity factor (Ω) because CO₂ and O₂ are both the substrates and the mutually competitive inhibitors for Rubisco. A simple integrated equation is proposed to calculate the CO₂/O₂ specificity factor (Ω). On the other hand, previous multi-step procedures, including the manipulation of radioisotope (¹⁴C and/or ³H) and the chromatographic separation of the products, are inconvenient and may cause much random error. An improved assay procedure is presented therefore, which includes the spectrophotometric measurement of 3-phosphoglycerate-dependent NADH oxidation with a coupled enzyme system. This revised version was published online in June 2006 with corrections to the Cover Date.     

滇中高原云南松林枯落物输入对土壤碳氮储量及其分布格局的影响

为了更好地理解土壤碳氮对枯落物输入变化的响应,通过枯落物添加与去除实验（DIRT）对滇中高原云南松林枯落物输入变化对土壤碳氮储量及其分布格局的影响进行了研究。2018年3月至2019年2月分别设置6种枯落物输处理,分别为对照（CO）、去除枯落物（NL）、双倍枯落物（DL）、去除根系（NR）、无输入（NI）以及去除有机层与A层（O/A-Less）,研究了不同处理条件下土壤剖面上碳氮储量的分布规律。研究结果表明：（1）不同处理全碳储量为134.49-170.92 t/hm²,全碳储量在不同处理间表现为：S_C（NL）=170.92 t/hm² > S_C（CO）=168.10 t/hm² > S_C（NR）=153.26 t/hm² > S_C（NI）=147.20 t/hm² > S_{C（O/A-Less）}=143.54 t/hm² > S_C（DL）=134.49 t/hm²,不同处理0-20 cm土层全碳储量占0-60 cm土层全碳储量的40.86%-53.56%;不同处理全氮储量表现为：S_N（CO）=11.83 t/hm² > S_N（NL）=9.70 t/hm² > S_N（DL）=8.70 t/hm² > S_N（NR）=8.35 t/hm² > S_{N（O/A-Less）}=8.21 t/hm² > S_N（NI）=8.09 t/hm²。不同处理0-20 cm土层的全氮储量占0-60 cm土层全氮储量的39.28%-46.04%。云南松林地枯落物添加去除实验发现去除枯落物短期内可以增加土壤碳储量,其他处理均在一定程度上减少了土壤碳氮储量。（2）地上枯落物输入对表层（0-20 cm）土壤碳氮影响显著,根系输入对深层（20-40 cm）土壤碳氮影响显著;（3）土壤C、N存在耦合关系,不同处理土壤全碳含量与全氮含量极显著正相关,并且土壤全碳含量与土壤各化学计量比均呈极显著正相关关系;土壤容重与土壤碳氮含量具有极显著负相关关系。     

Carbon budgeting in plant–soil mesocosms under elevated CO2: locally missing carbon?

Studies have suggested that more carbon is fixed due to a large increase in photosynthesis in plant–soil systems exposed to elevated CO₂ than could subsequently be found in plant biomass and soils –‐ the locally missing carbon phenomenon. To further understand this phenomenon, an experiment was carried out using EcoCELLs which are open‐flow, mass‐balance systems at the mesocosm scale. Naturally occurring ¹³C tracers were also used to separately measure plant‐derived carbon and soil‐derived carbon. The experiment included two EcoCELLs, one under ambient atmospheric CO₂ and the other under elevated CO₂ (ambient plus 350 μL L^{? 1}). By matching carbon fluxes with carbon pools, the issue of locally missing carbon was investigated. Flux‐based net primary production (NPP_f) was similar to pool‐based primary production (NPP_p) under ambient CO₂, and the discrepancy between the two carbon budgets (12 g C m^{? 2}, or 4% of NPP_f) was less than measurement errors. Therefore, virtually all carbon entering the system under ambient CO₂ was accounted for at the end of the experiment. Under elevated CO₂, however, the amount of NPP_f was much higher than NPP_p, resulting in missing carbon of approximately 80 g C m^{? 2} or 19% of NPP_f which was much higher than measurement errors. This was additional to the 96% increase in rhizosphere respiration and the 50% increase in root growth, two important components of locally missing carbon. The mystery of locally missing carbon under elevated CO₂ remains to be further investigated. Volatile organic carbon, carbon loss due to root washing, and measurement errors are discussed as some of the potential contributing factors.     

Carbon accumulation, distribution and water use of Danthonia richardsonii swards in response to CO2 and nitrogen supply over four years of growth

Microcosms of Danthonia richardsonii (Cashmore) accumulated more carbon when grown under CO₂ enrichment (719 μL L^–1 cf. 359 μL L^–1) over a four-year period, even when nitrogen availability severely restricted productivity (enhancement ratios for total microcosm C accumulation of 1.21, 1.14 and 1.29 for mineral N supplies of 2.2, 6.7 and 19.8 g N m^–2 y^–1, respectively). The effect of CO₂ enrichment on total system carbon content did not diminish with time. Increased carbon accumulation occurred despite the development over time of a lower leaf area index and less carbon in the green leaf fraction at high CO₂. The extra carbon accumulated at high CO₂ in the soil, senesced leaf and leaf litter fractions at all N levels, and in root at high-N, while at low-and mid-N less carbon accumulated in the root fraction at high CO₂. The rate of leaf turnover was increased under CO₂ enrichment, as indicated by increases in the carbon mass ratio of senesced to green leaf lamina. Microcosm evapotranspiration rates were lower at high CO₂ when water was in abundant supply, resulting in higher average soil water contents. The higher soil water contents at high CO₂ have important implications for microcosm function, and may have contributed significantly to the increased carbon accumulation at high CO₂. These results indicate that CO₂ enrichment can increase carbon accumulation by a simple soil–plant system, and that any increase in whole system carbon accumulation may not be evident from snapshot measurements of live plant carbon.     

Allocation and Turnover of Photosynthetically Assimilated CO(2) in Leaves of Glycine max L. Clark

The allocation and turnover of photosynthetically assimilated ¹⁴CO₂ in lipid and protein fractions of soybean (Glycine max L. Clark) leaves and stem materials was measured. In whole plant labeling experiments, allocation of photosynthate from a pulse of ¹⁴CO₂ into polymeric compounds was: 25% to proteins in 4 days, 20% to metabolically inert cell wall products in 1 to 2 days, 10% to lipids in 4 days, and 4% to starch in 1 day. The amount of ¹⁴C labeled photosynthate that an actively growing leaf (leaf 4) used for its own lipid synthesis immediately following pulse labeling was about 25%. The ¹⁴C of labeled proteins turned over with half-lives of 3.8, 3.3, and 4.1 days in leaves 1, 2, and 3, respectively; and turnover of ¹⁴C in total shoot protein proceeded with a half-life of 5.2 days. Three kinetic ¹⁴C turnover patterns were observed in lipids: a rapid turnover fraction (within a day), an intermediate fraction (half-life about 5 days), and a slow turnover fraction. These results are discussed in terms of previously published accounts of translocation, carbon budgets, carbon use, and turnover in starch, lipid, protein, and cell wall materials of various plants including soybeans.     

Nature of FeSe2/N‐C Anode for High Performance Potassium Ion Hybrid Capacitor

Potassium ion hybrid capacitors have great potential for large‐scale energy devices, because of the high power density and low cost. However, their practical applications are hindered by their low energy density, as well as electrolyte decomposition and collector corrosion at high potential in potassium bis(fluoro‐sulfonyl)imide‐based electrolyte. Therefore, anode materials with high capacity, a suitable voltage platform, and stability become a key factor. Here, N‐doping carbon‐coated FeSe₂ clusters are demonstrated as the anode material for a hybrid capacitor, delivering a reversible capacity of 295 mAh g^?1 at 100 mA g^?1 over 100 cycles and a high rate capability of 158 mAh g^?1 at 2000 mA g^?1 over 2000 cycles. Meanwhile, through density functional theory calculations, in situ X‐ray diffraction, and ex situ transmission electron microscopy, the evolution of FeSe₂ to Fe₃Se₄ for the electrochemical reaction mechanism is successfully revealed. The battery‐supercapacitor hybrid using commercial activated carbon as the cathode and FeSe₂/N‐C as the anode is obtained. It delivers a high energy density of 230 Wh kg^?1 and a power density of 920 W kg^?1 (the energy density and power density are calculated based on the total mass of active materials in the anode and cathode).     

Potentiometric measurements of carbon dioxide flux of submerged aquatic macrophytes in pH-statted natural waters

SUMMARY. 1, An apparatus has been described that is suitable for potentiometric measurement of carbon dioxide flux in photosynthesizing shoots of submerged aquatic macrophytes 2. The procedure, based on methods described by Tailing (1973) for measurement of phytoplankton photosynthesis, relies upon the continuous pH-statting of the solution surrounding the tissues. The pH of the solution is monitored by electrodes from a pH meter which is linked to an auto-titrator. The rise in pH during photosynthesis is then compensated tor by controlled, small titrant additions of CO₂-ennched solution (titrant water). This replaces the CO₂ removed by the tissues without affecting the total alkalinity of the solution. If the concentration of CO₂ in the titrant water, and the volume of titrant added arc known precisely, the CO₂ flux can be calculated. 3. Total alkalinity, total CO₂ and free-CO₂ acidity of the bathing solutions and titrant waters are estimated by Gran titrations and the pH: tilre-volume data pairs are analysed by computer to provide rapid data feed-back. A modification to Tailing's equation for calculation of F₁functions has been necessary for accurate calibration of the CO₂enriched tilrant water. 4. The photosynthesis cuvette, which is surrounded by a water-jacket, is approximately I dm³ in capacity and has six compartments for the shoots. An impeller at the base of the cuvette rapidly mixes and cycles the bathing solution and flushes it over the tissues. 5. Information on temperature, light flux density, oxygen concentration. pH and titre-volume is continuously recorded into a data-logger and is fed into a computer which is programmed for data analyses. 6. Results from a typical experiment show the system to be sound and the method has considerable potential, especially in the study of aquatic plant photosynthesis in natural waters.     

Exploiting the Condensation Reactions of Acetophenone to Engineer Carbon‐Encapsulated Nb2O5 Nanocrystals for High‐Performance Li and Na Energy Storage Systems

Efficient synthetic methods to produce high‐performance electrode‐active materials are crucial for developing energy storage devices for large‐scale applications, such as hybrid supercapacitors (HSCs). Here, an effective approach to obtain controllable carbon‐encapsulated T‐Nb₂O₅ nanocrystals (NCs) is presented, based on the solvothermal treatment of NbCl₅ in acetophenone. Two separate condensation reactions of acetophenone generate an intimate and homogeneous mixture of Nb₂O₅ particles and 1,3,5‐triphenylbenzene (TPB), which acts as a unique carbon precursor. The electrochemical performance of the resulting composites as anode electrode materials can be tuned by varying the Nb₂O₅/TPB ratio. Remarkable performances are achieved for Li‐ion and Na‐ion energy storage systems at high charge–discharge rates (specific capacities of ≈90 mAh g^?1 at 100 C rate for lithium and ≈125 mAh g^?1 at 20 C for sodium). High energy and power densities are also achieved with Li‐ and Na‐ion HSC devices constructed by using the Nb₂O₅/C composites as anode and activated carbon (YPF‐50) as cathode, demonstrating the excellent electrochemical properties of the materials synthesized with this approach.     

Measurement of the Concentration of the Active Centers of Ribulose-1,5-bisphosphate Carboxylase/Oxygenase in vivo

Methods for in vivo measurement of the concentration of the reactive centers of ribulose-1,5,-bisphosphate carboxylase/oxygenase (Rubisco) are suggested that are based on saturation of the active centers with RuBP and determination of the concentration of the Rubisco–RuBP complex. The total concentration of potentially reactive centers is calculated from the dependence of the concentration of this complex on CO₂ concentration at a steady-state photosynthetic rate with further extrapolation of the carbon dioxide dependence curve to a zero CO₂ concentration. The concentration of centers that possessed a catalytic activity under given environmental conditions was measured after transferring leaves having a steady-state photosynthetic rate into a medium devoid of CO₂ and O₂. This procedure ensured the saturation of the carboxylation centers with RuBP. The carboxylation rates were measured during a short-term exposure to ¹⁴CO₂, and the concentration of the complex was calculated using the values of CO₂ concentration during the exposure time, as well as the carboxylation rate and constant. Rubisco activity was found to decrease at elevated CO₂ concentrations due to a lower concentration of catalytically active enzyme centers.     

Influence of carbon availability on the production of NO, N2O, N2 and CO2 by soil cores during anaerobic incubation

Net productions of permanent soil atmosphere gases (N₂, CO₂, O₂) and temporary gases (N₂O, NO) were monitored in soil cores using a non-interfering, fully automated measuring technique allowing highly time resolved measurements over prolonged periods. The influence of changes in available organic carbon on CO₂, N₂O, NO and N₂ production was studied by changing the soil carbon content through aerobic preincubations of different length, up to 21 days.The aerobic preincubation caused an increase in NO₃ ^- concentration and a decrease in available carbon content. Available carbon content dominated both CO₂ and total N gas (N₂+N₂O+NO) production during anaerobiosis. Both CO₂ and total N gas production rates decreased with increasing length of the previous aerobic preincubation, this in spite of the higher initial NO₃ ^- concentration.Total denitrification rates were closely related to the anaerobic CO₂ production rates. No relation was found between water soluble carbon content and total denitrification. The N₂O/N₂ ratio could be explained by an interaction of carbon availability, NO₃ ^- concentration and enzyme status. Net N₂O consumption was monitored. The balance between cumulative total N gas production and NO₃ ^- consumption varied according to the different treatments. Cumulative N₂O production exceeded cumulative N₂ production for 0 up to 5 days.     

北京市主要建筑保温材料生命周期与环境经济效益评价

在低碳、绿色、环保、生态成为当代城市文明的主题下,建筑保温材料作为建筑节能最主要的解决途径之一备受关注,以北京市75%节能6层模拟住宅为例,利用DeST-h软件计算得出其墙体传热系数K值为0.40 W m-2K-1,节约电量42.31 kW h-1m-2,通过计算可节约标煤17.09 kg/m2,减少CO2排放量42.19 kg/m2,减少SO2排放量1.27 kg/m2,减少NOx排放量0.635 kg/m2,减少煤粉尘排放量11.5 kg/m2,减少煤烟尘排放5.75 kg/m2,环境效益36.66元/m2。并利用生命周期原理进行简化计算出4种常见保温材料岩棉、XPS、EPS和聚氨酯的50a建筑寿命周期中的总能耗分别为6.55×106、6.63×106、6.58×106、6.77×106kJ/m2,其中不同阶段能耗所占的比例从大到小依次为运行能耗生产能耗运输能耗。保温材料资金回收年限、环境效益回收年限和能耗回收年限的大小顺序:聚氨酯XPS≈EPS岩棉,三者顺序基本一致。并对建筑外墙保温材料科学评价与发展趋势进行探讨。     

Tunable Polyaniline‐Based Porous Carbon with Ultrahigh Surface Area for CO2 Capture at Elevated Pressure

Natural gas is the cleanest fossil fuel source. However, natural gas wells typically contain considerable amounts of CO₂, with on‐site CO₂ capture necessary. Solid sorbents are advantageous over traditional amine scrubbing due to their relatively low regeneration energies and non‐corrosive nature. However, it remains a challenge to improve the sorbent's CO₂ capacity at elevated pressures relevant to natural gas purification. Here, the synthesis of porous carbons derived from a 3D hierarchical nanostructured polymer hydrogel, with simple and effective tunability over the pore size distribution is reported. The optimized surface area reaches 4196 m² g^?1, which is among the highest of carbon‐based materials, with abundant micro‐ and narrow mesopores (2.03 cm³ g^?1 with d < 4 nm). This carbon exhibits a record‐high CO₂ capacity among reported carbons at elevated pressure (i.e., 28.3 mmol g^?1 total adsorption at 25 °C and 30 bar). This carbon also shows good CO₂/CH₄ selectivity and excellent cyclability. Molecular simulations suggest increased CO₂ density in micro‐ and narrow mesopores at high pressures. This is consistent with the observation that these pores are mainly responsible for the material's high‐pressure CO₂ capacity. This work provides insights into material design and further development for CO₂ capture from natural gas.     

Interconnected Frameworks with a Sandwiched Porous Carbon Layer/Graphene Hybrids for Supercapacitors with High Gravimetric and Volumetric Performances

A facile approach to synthesize porous disordered carbon layers as energy storage units coating on graphene sheets to form interconnected frameworks by one‐step pyrolysis of the mixture of graphene oxide/polyaniline and KOH is presented. As effective energy storage units, these porous carbon layers play an important role in enhancing the electrochemical performances. The obtained porous carbon material exhibits a high specific surface area (2927 m² g^?1), hierarchical interconnected pores, moderate pore volume (1.78 cm³ g^?1), short ion diffusion paths, and a high nitrogen level (6 at%). It displays both unparalleled gravimetric (481 F g^?1) and outstanding volumetric capacitance (212 F cm^?3) in an aqueous electrolyte. More importantly, the assembled symmetrical supercapacitor delivers not only high gravimetric (25.7 Wh kg^?1 based on total mass of electroactive materials) but also high volumetric energy densities (11.3 Wh L^?1) in an aqueous electrolyte. Furthermore, the assembled asymmetric supercapacitor yields a maximum energy density up to 88 Wh kg^?1, which is, to the best of our knowledge, the highest value so far reported for carbon//MnO₂ asymmetric supercapacitors in aqueous electrolytes. Therefore, this novel carbon material holds great promise for potential applications in energy‐related technological fields.     

Contribution of Lolium perenne rhizodeposition to carbon turnover of pasture soil

Carbon rhizodeposition and root respiration during eight development stages of Lolium perenne were studied on a loamy Gleyic Cambisol by ¹⁴CO₂ pulse labelling of shoots in a two compartment chamber under controlled laboratory conditions. Total ¹⁴CO₂ efflux from the soil (root respiration, microbial respiration of exudates and dead roots) in the first 8 days after ¹⁴C pulse labelling decreased during plant development from 14 to 6.5% of the total ¹⁴C input. Root respiration accounted for was between 1.5 and 6.5% while microbial respiration of easily available rhizodeposits and dead root remains were between 2 and 8% of the ¹⁴C input. Both respiration processes were found to decline during plant development, but only the decrease in root respiration was significant. The average contribution of root respiration to total ¹⁴CO₂ efflux from the soil was approximately 41%. Close correlation was found between cumulative ¹⁴CO₂ efflux from the soil and the time when maximum ¹⁴CO₂ efflux occurred (r=0.97). The average total of CO₂ Defflux from the soil with Lolium perenne was approximately 21 μg C-CO₂ d⁻¹ g⁻¹. It increased slightly during plant development. The contribution of plant roots to total CO₂ efflux from the soil, calculated as the remainder from respiration of bare soil, was about 51%. The total ¹⁴C content after 8 days in the soil with roots ranged from 8.2 to 27.7% of assimilated carbon. This corresponds to an underground carbon transfer by Lolium perenne of 6–10 g C m⁻² at the beginning of the growth period and 50–65 g C m⁻² towards the end of the growth period. The conventional root washing procedure was found to be inadequate for the determination of total carbon input in the soil because 90% of the young fine roots can be lost. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

Carbon dioxide exchange of a Russian boreal forest after disturbance by wind throw

The exchange of carbon dioxide (CO₂) between the atmosphere and a forest after disturbance by wind throw in the western Russian taiga was investigated between July and October 1998 using the eddy covariance technique. The research area was a regenerating forest (400 m × 1000 m), in which all trees of the preceding generation were uplifted during a storm in 1996. All deadwood had remained on site after the storm and had not been extracted for commercial purposes. Because of the heterogeneity of the terrain, several micrometeorological quality tests were applied. In addition to the eddy covariance measurements, carbon pools of decaying wood in a chronosequence of three different wind throw areas were analysed and the decay rate of coarse woody debris was derived. During daytime, the average CO₂ uptake flux was ?3 µmol m^?2s^?1, whereas during night‐time characterised by a well‐mixed atmosphere the rates of release were typically about 6 µmol m^?2s^?1. Suppression of turbulent fluxes was only observed under conditions with very low friction velocity (u* ≤ 0.08 ms^?1). On average, 164 mmol CO₂ m^?2d^?1 was released from the wind throw to the atmosphere, giving a total of 14.9 mol CO₂ m^?2 (180 g CO₂ m^?2) released during the 3‐month study period. The chronosequence of dead woody debris on three different wind throw areas suggested exponential decay with a decay coefficient of ?0.04 yr^?1. From the magnitude of the carbon pools and the decay rate, it is estimated that the decomposition of coarse woody debris accounted for about a third of the total ecosystem respiration at the measurement site. Hence, coarse woody debris had a long‐term influence on the net ecosystem exchange of this wind throw area. From the analysis performed in this work, a conclusion is drawn that it is necessary to include into flux networks the ecosystems that are subject to natural disturbances and that have been widely omitted into considerations of the global carbon budget. The half‐life time of about 17 years for deadwood in the wind throw suggests a fairly long storage of carbon in the ecosystem, and indicates a very different long‐term carbon budget for naturally disturbed vs. commercially managed forests.     

Temperature and precipitation drive temporal variability in aquatic carbon and GHG concentrations and fluxes in a peatland catchment

The aquatic pathway is increasingly being recognized as an important component of catchment carbon and greenhouse gas (GHG) budgets, particularly in peatland systems due to their large carbon store and strong hydrological connectivity. In this study, we present a complete 5‐year data set of all aquatic carbon and GHG species from an ombrotrophic Scottish peatland. Measured species include particulate and dissolved forms of organic carbon (POC, DOC), dissolved inorganic carbon (DIC), CO₂, CH₄ and N₂O. We show that short‐term variability in concentrations exists across all species and this is strongly linked to discharge. Seasonal cyclicity was only evident in DOC, CO₂ and CH₄ concentration; however, temperature correlated with monthly means in all species except DIC. Although the temperature correlation with monthly DOC and POC concentrations appeared to be related to biological productivity in the terrestrial system, we suggest the temperature correlation with CO₂ and CH₄ was primarily due to in‐stream temperature‐dependent solubility. Interannual variability in total aquatic carbon concentration was strongly correlated with catchment gross primary productivity (GPP) indicating a strong potential terrestrial aquatic linkage. DOC represented the largest aquatic carbon flux term (19.3 ± 4.59 g C m^?2 yr^?1), followed by CO₂ evasion (10.0 g C m^?2 yr^?1). Despite an estimated contribution to the total aquatic carbon flux of between 8 and 48%, evasion estimates had the greatest uncertainty. Interannual variability in total aquatic carbon export was low in comparison with variability in terrestrial biosphere–atmosphere exchange, and could be explained primarily by temperature and precipitation. Our results therefore suggest that climatic change is likely to have a significant impact on annual carbon losses through the aquatic pathway, and as such, aquatic exports are fundamental to the understanding of whole catchment responses to climate change.     

The effect of carbon dioxide concentration on respiration of growing and mature soybean leaves

Soybean plants were grown continuously at 350 and 700cm³m^?3 CO₂ at constant temperature. Respiration rates of third trifoliolate leaves were measured at the growth CO₂ concentration for the whole dark period from 5d before through to 5d after full area expansion. The short-term response of respiration rate to the measurement CO₂ concentration was also determined at each age. Respiration rates per unit of dry mass declined with age and were significantly less at a given age or RGR in leaves grown and measured at the elevated CO₂. The difference in respiration rate was largest in mature leaves and resulted from the different measurement CO₂ concentrations. The respiratory costs of the tissue synthesis, estimated from the elemental composition of the tissue, did not differ substantially between CO₂ treatments. The response of respiration rate to carbon dioxide concentration was not strongly affected by the form of nitrogen supplied. Maintenance respiration calculated by subtracting growth respiration from total respiration was negative in rapidly growing leaves for both CO₂ treatments. This indicates that CO₂ efflux in the dark does not accurately reflect the average 24 h rate of energy expenditure on growth and maintenance for soybean leaves.     

Climatic variability,hydrologic anomaly,and methane emission can turn productive freshwater marshes into net carbon sources

Freshwater marshes are well‐known for their ecological functions in carbon sequestration, but complete carbon budgets that include both methane (CH₄) and lateral carbon fluxes for these ecosystems are rarely available. To the best of our knowledge, this is the first full carbon balance for a freshwater marsh where vertical gaseous [carbon dioxide (CO₂) and CH₄] and lateral hydrologic fluxes (dissolved and particulate organic carbon) have been simultaneously measured for multiple years (2011–2013). Carbon accumulation in the sediments suggested that the marsh was a long‐term carbon sink and accumulated ~96.9 ± 10.3 (±95% CI) g C m^?2 yr^?1 during the last ~50 years. However, abnormal climate conditions in the last 3 years turned the marsh to a source of carbon (42.7 ± 23.4 g C m^?2 yr^?1). Gross ecosystem production and ecosystem respiration were the two largest fluxes in the annual carbon budget. Yet, these two fluxes compensated each other to a large extent and led to the marsh being a CO₂ sink in 2011 (?78.8 ± 33.6 g C m^?2 yr^?1), near CO₂‐neutral in 2012 (29.7 ± 37.2 g C m^?2 yr^?1), and a CO₂ source in 2013 (92.9 ± 28.0 g C m^?2 yr^?1). The CH₄ emission was consistently high with a three‐year average of 50.8 ± 1.0 g C m^?2 yr^?1. Considerable hydrologic carbon flowed laterally both into and out of the marsh (108.3 ± 5.4 and 86.2 ± 10.5 g C m^?2 yr^?1, respectively). In total, hydrologic carbon fluxes contributed ~23 ± 13 g C m^?2 yr^?1 to the three‐year carbon budget. Our findings highlight the importance of lateral hydrologic inflows/outflows in wetland carbon budgets, especially in those characterized by a flow‐through hydrologic regime. In addition, different carbon fluxes responded unequally to climate variability/anomalies and, thus, the total carbon budgets may vary drastically among years.