广州地区晚稻田CH4和N2O的排放通量及其影响因素

用密闭箱法同时研究了广州地区晚稻田CH4和N2 O的排放通量。结果表明 ,连续淹水、常规连作和水旱轮作等 3种处理的CH4平均排放通量分别为 1 7 63、2 84和0 36mg·m- 2 ·h- 1 ,而N2 O的平均排放通量分别为 6 74、1 1 69和 55 0 7μgN2 O N·m- 2 ·h- 1 ,表明稻田连续淹水显著增加CH4的排放而降低N2 O的排放。水旱轮作降低CH4排放而提高N2 O的排放 ,说明稻田CH4和N2 O排放之间存在着消长关系。讨论了这 2种温室气体排放的影响因素 ,并初步分析了它们对温室效应的相对贡献。     

施氮对桉树人工林生长季土壤温室气体通量的影响

施肥是维持短期轮伐人工林生产量的重要手段,为了提高肥料利用效率,缓释氮肥逐渐成为广泛采用的氮肥种类。评估缓释肥施用对人工林生长季土壤温室气体通量的影响对于全面评估人工林施肥的环境效应具有重要意义。以我国南方广泛种植的桉树林为对象,采用野外控制实验研究了4种施氮处理(对照CK:0 kg/hm2;低氮L:84.2 kg/hm2;中氮M:166.8 kg/hm2;高氮H:333.7 kg/hm2)对土壤-大气界面3种温室气体(CO2、N2O和CH4)通量的影响,结果表明:(1)4种施氮水平下CO2排放通量、N2O排放通量和CH4吸收通量分别为276.84—342.84 mg m-2h-1、17.64—375.34μg m-2h-1和29.65—39.70μg m-2h-1;施氮显著促进了N2O的排放(P0.01),高氮处理显著增加CO2排放和显著减少CH4吸收(P0.05),且CO2排放通量与CH4吸收通量随着施氮量的增加分别呈现增加和减少的趋势;(2)生长季CO2和N2O排放呈现显著正相关(P0.01),CO2排放和CH4吸收呈现显著负相关(P0.05),N2O排放和CH4吸收呈现显著负相关(P0.01);(3)土壤温度和土壤水分是影响CO2、N2O排放通量和CH4吸收通量的主要环境因素。结果表明:施用缓释肥显著增加了桉树林生长季土壤N2O排放量,且高氮处理还显著促进CO2排放和显著抑制CH4吸收,上述研究结果可为人工林缓释肥对土壤温室气体通量评估提供参数。     

小兴安岭阔叶林沼泽土壤CO_2、CH_4和N_2O排放规律及其影响因子

采用野外静态箱-气相色谱法,研究了小兴安岭典型阔叶林沼泽生长季节土壤CO2、CH4和N2O排放季节变化规律、源/汇功能及主要影响因子。结果表明:①苔草沼泽、毛赤杨沼泽和白桦沼泽生长季节土壤CO2、CH4、N2O排放分别集中在夏季、夏秋季、春夏季,平均排放通量依次为487.89、382.27、514.63 mg.m-2.h-1,1.88、1.03、0.04 mg.m-2.h-1,3.70、58.61、11.73μg.m-2.h-1。②三者生长季节土壤CO2排放通量与气温和0-20 cm土壤温度均呈显著正相关;苔草沼泽CH4排放通量与30-40cm土壤温度呈显著正相关,毛赤杨沼泽CH4排放通量与地表温度呈显著负相关;白桦沼泽N2O排放通量与地表温度呈显著正相关。苔草沼泽N2O排放与水位呈显著负相关;毛赤杨沼泽CH4排放与水位呈显著正相关;白桦沼泽CO2排放与水位呈显著负相关。③三者生长季节土壤均为CO2、CH4、N2O排放源(17.56、13.76、18.53 t.hm-2;67.54、37.05、1.30 kg.hm-2;0.13、2.11、0.42 kg.hm-2),三者CO2排放量相近(5.5%-21.6%);苔草沼泽为CH4的强排放源,毛赤杨沼泽为中排放源,白桦沼泽为弱排放源;毛赤杨沼泽为N2O的强排放源,白桦沼泽为中排放源,苔草沼泽为弱排放源。     

华南丘陵地区农林复合生态系统晚稻田甲烷和氧化亚氮排放

采用静态箱-气相色谱法对晚稻田甲烷(CH4)和氧化亚氮(N2O)排放进行田间原位测定。结果表明,有植株参与的稻田CH4排放通量季节变化与地下5cm温度呈显著正相关关系。稻田CH4和N2O季节平均排放通量在有植株参与时分别为1.16±0.38mgm-2h-1和42.33±20.00μgm-2h-1,而无植株参与的分别为0.15±0.11mgm-2h-1和51.69±15.87μgm-2h-1。水稻种植对CH4的排放影响较大,对N2O的排放影响较小,有植株参与的稻田CH4平均排放量显著高于无植株参与的稻田,N2O的平均排放量无显著差异。     

开放式空气CO2增高对稻田CH4和N2O排放的影响

在FACE(free aircarbondioxideenrichment)平台上 ,采用静态暗箱 气相色谱法观测研究了大气CO2 浓度增加对稻田CH4和N2 O排放的影响 .结果表明 ,在 15 0和 2 5 0kgN·hm-2 两种氮肥水平下大气CO2 浓度增加 2 0 0 μmol·mol-1均明显促进水稻生长 ,水稻生物量积累 .大气CO2 浓度增加对 15 0和 2 5 0kgN·hm-2 两种氮肥水平下稻田CH4排放均无显著影响 ,并简要分析了与现有文献报道结果不一致的原因 .大气CO2 浓度增加也未导致 15 0和 2 5 0kgN·hm-2 两种氮肥水平下稻田N2 O排放的明显变化 ,与大多数研究结果一致 .     

青藏高原高寒草原碳排放及其迁移过程研究

采用箱式法通过对青海省五道梁地区高寒草原生态系统表层土壤含碳温室气体的研究发现 ,该地区高寒草原系统表层土壤 CO2 和 CH4 在 7～ 8月份的平均排放通量分别为 0 .46μmol· m- 2 · s- 1和 - 0 .43× 1 0 - 3μmol·m- 2 ·s- 1,此两种气体的排放通量随时间都有明显的变化特征 ,它们的日变化均为明显的单峰型 ,而且其中 CO2 排放通量的变化明显受大气温度变化的影响。地下土壤中 CO2 和 CH4 气体浓度随深度的增加呈递减趋势 ,进一步的分析表明这两种气体浓度在土壤中与相邻层次的气体浓度有很明显的相关关系 ,尤以永久冻土上层边界附近最为显著。     

稻草覆盖对冬闲稻田二氧化碳通量的影响

通过研究稻草覆盖对土壤含水量、土壤温度及田间杂草生长的影响,探讨了亚热带红壤性稻田生态系统冬闲期稻草覆盖对CO2通量的影响及其机理.结果表明:稻草覆盖主要通过两个途径影响冬闲稻田的CO2通量:一是稻草覆盖对土壤温度有正效应,使稻田生态系统CO2排放量显著增加,试验期间覆盖处理平均净排放1.99 g CO2·m-2·d-1,而对照处理平均净吸收2.68 g CO2·m-2·d-1,两者差异达极显著水平(P《0.01);二是稻草覆盖使田间杂草的生物量及其吸收的光合有效辐射显著减少, 导致覆盖处理白天CO2排放量提高.稻草覆盖处理土壤表层(0～15 cm)相对含水量比无覆盖处理提高了9%以上,但未对CO2通量的变化产生显著影响.     

大气CO2增加对陆地生态系统微量气体地-气交换的影响

简要综述了近年来国内外在大气CO2浓度增加对微量气体交换影响方面的研究进展,首先介绍了有关大气CO2浓度增加的研究技术和方法,比较了目前两种常用技术开顶箱（OTC）和开放式空气CO2增加（FACE）方法的优缺点,然后着重阐述了用OTC和FACE研究陆地生态系统CH4、N2O、CO2等微量气体的地气交换对大气CO2浓度增加的响应,综合现有的资料表明,大气CO2浓度增加,会促进绿色植物生物量增加,同时改变生物质的C/N,降低有机质的分解速率,增强了陆地生态系统对大气CO2的固特作用;大气CO2浓度增加会提高产甲烷菌的活性和影响CH4的排放过程,有可能导致湿地生态系统CH4的排放增加;大气CO2浓度增加对N2O排放影响的研究较少,且尚无一致的结论;另外,对于其他微量气体,尚没有盯关研究报道,鉴于此,今后应加强大气CO2浓度增加的微量气体地气交换响应研究。     

华南丘陵区农林复合生态系统稻田二氧化碳排放及其影响因素

采用静态箱-气相色谱法对稻田CO2排放进行田间原位测定,探讨农林复合生态系统稻田温室气体CO2的排放规律。结果表明,在生长季节中,有植株参与稻田CO2排放速率的日变化形式均为白天出现排放高值,夜间出现排放低值。有植株参与稻田CO2昼夜排放速率平均值都显著高于无植株参与稻田。温度(气温、地表温度、地下5 cm温度)是有植株参与稻田在植株生长期间稻田CO2排放速率昼夜变化的主要影响因素。水稻作物对CO2的排放影响较大,早稻有、无植株参与稻田CO2季节平均排放速率分别为316.29±23.74和101.88±16.83 mg.m-2.h-1。晚稻有、无植株参与稻田CO2季节平均排放速率分为622.40±57.67和179.41±19.51 mg.m-2.h-1。早、晚稻有植株参与稻田的CO2季节平均排放量分别比无植株参与稻田增加了310%和347%。     

青藏高原高寒草甸非生长季温室气体排放特征及其年度贡献

高寒草甸是青藏高原地区的主要植被类型,目前对其温室气体研究多集中于生长季.本文利用静态箱-气相色谱法,对非生长季高寒草甸温室气体排放特征及其与主要环境因子的关系进行了研究.结果表明:非生长季高寒草甸表现为CO2和N2O的源、CH4的汇.其中非生长季CO2通量平均值为89.33 mg·m-2·h-1,累积排放通量为280.01g· m-2;CH4通量平均值为-11.35 μg·m-2·h-1,累积吸收通量为124.74 mg·m-2;N2O通量平均值为8.02 μg·m-2·h-1,累积排放通量为39.51 mg·m-2.非生长季CO2、CH4和N2O累积排放通量分别占全年的13.33％、53.47％和62.67％.冻融期(2012年4月)CH4累积吸收通量较小,只占非生长季的4.5％;而CO2和N2O累积排放通量较大,分别占非生长季的25.8％和20.8％.非生长季CO2通量与温度(气温、5和10 cm土壤温度)和5 cm土壤湿度均存在显著正相关关系,而CH4和N2O通量仅与5 cm土壤湿度存在显著正相关.研究表明,虽然冻融期CH4累积吸收通量在非生长季累积量中比重较小,但非生长季CH4和N2O累积排放量却占全年累积排放量的1/2以上,在温室气体累积通量评估中不容忽视.     

Dual emission carbon dots from carotenoids: Converting a single emission to dual emission

Dual emission carbon dots have a high potential for use as fluorescence‐based sensors with higher selectivity and sensitivity. This study demonstrated the possibility of conversion of a biological molecular system with a single emission peak to a double emission carbon dots system. This report is the first to describe the synthesis of dual emission carbon dots by tuning the electronic environment of a conjugated system. Here we prepared carbon dots from a natural extract, from which carotenoids were used as a new source for carbon dots. Formation of the carbon dots was confirmed by images obtained under a transmission electron microscope as well as from a dynamic light scattering study. The prepared carbon dots system was characterized and its optical property was monitored. The study showed that, after irradiation with microwaves, the fluorescence intensity of the whole system changed, without any change in the original peak position of the carotenoid but with the appearance of an additional peak. A Fourier transform infrared study confirmed breaking of the conjugated system. When using ethylene glycol as a surface passivating agent added to these carotenoid carbon dots, the dual emission spectra became more distinct.     

Methane emission from Arctic tundra

Concerns about a possible feedback effect on global warming following possible increased emissions of methane from tundra environments have lead to series of methane flux studies of northern wetland/tundra environments. Most of these studies have been carried out in boreal sub-Arctic regions using different techniques and means of assessing representativeness of the tundra. Here are reported a time series of CH₄ flux measurements from a true Arctic tundra site. A total of 528 independent observations were made at 22 fixed sites during the summers of 1991 and 1992. The data are fully comparable to the most extensive dataset yet produced on methane emissions from sub-Arctic tundra-like environments. Based on the data presented, from a thaw-season with approximately 55% of normal precipitation, a global tundra CH₄ source of 18–30 Tg CH₄ yr⁻¹ is estimated. This is within the range of 42±26 Tg CH₄ yr⁻¹ found in a similar sub-Arctic tundra environment. No single-parameter relationship between one environmental factor and CH₄ flux covering all sites was found. This is also in line with conclusions drawn in the sub-Arctic. However, inter-season variations in CH₄ flux at dry sites were largely controlled by the position of the water table, while flux from wetter sites seemed mainly to be controlled by soil temperature.     

Accelerated electrons and hard X-ray emission from X-pinches

The generation of accelerated electrons in the X-pinch minidiode is studied experimentally. It is well known that the explosion of an X-pinch consisting of two or more wires is accompanied by the formation of a minidiode, in which electrons are accelerated. The subsequent slowing down of electrons in the products of wire explosion causes the generation of hard X-ray (HXR) emission with photon energies higher than 10 keV. In this work, the spatial and temporal characteristics of X-pinch HXR emission are studied, the specific features of HXR generation are discussed, and the capability of applying this radiation to point-projection X-ray imaging of various plasma and biological objects is considered. The parameters of the electron beam produced in the X-pinch are measured using a Faraday cup and X-ray diagnostics. The experiments were performed with the XP generator (550 kA, 100 ns) at Cornell University (United States) and the BIN generator (270 kA, 150 ns) at the Lebedev Physical Institute (Russia).     

Isoprene emission from plants: why and how

BACKGROUND: Some, but not all, plants emit isoprene. Emission of the related monoterpenes is more universal among plants, but the amount of isoprene emitted from plants dominates the biosphere-atmosphere hydrocarbon exchange. SCOPE: The emission of isoprene from plants affects atmospheric chemistry. Isoprene reacts very rapidly with hydroxyl radicals in the atmosphere making hydroperoxides that can enhance ozone formation. Aerosol formation in the atmosphere may also be influenced by biogenic isoprene. Plants that emit isoprene are better able to tolerate sunlight-induced rapid heating of leaves (heat flecks). They also tolerate ozone and other reactive oxygen species better than non-emitting plants. Expression of the isoprene synthase gene can account for control of isoprene emission capacity as leaves expand. The emission capacity of fully expanded leaves varies through the season but the biochemical control of capacity of mature leaves appears to be at several different points in isoprene metabolism. CONCLUSIONS: The capacity for isoprene emission evolved many times in plants, probably as a mechanism for coping with heat flecks. It also confers tolerance of reactive oxygen species. It is an example of isoprenoids enhancing membrane function, although the mechanism is likely to be different from that of sterols. Understanding the regulation of isoprene emission is advancing rapidly now that the pathway that provides the substrate is known.     

Carbon dioxide emission from bamboo culms

Bamboos are one of the fastest growing plants on Earth, and are widely considered to have high ability to capture and sequester atmospheric carbon, and consequently to mitigate climate change. We tested this hypothesis by measuring carbon dioxide (CO₂) emissions from bamboo culms and comparing them with their biomass sequestration potential. We analysed diurnal effluxes from Bambusa vulgaris culm surface and gas mixtures inside hollow sections of various bamboos using gas chromatography. Corresponding variations in gas pressure inside the bamboo section and culm surface temperature were measured. SEM micrographs of rhizome and bud portions of bamboo culms were also recorded. We found very high CO₂ effluxes from culm surface, nodes and buds of bamboos. Positive gas pressure and very high concentrations of CO₂ were observed inside hollow sections of bamboos. The CO₂ effluxes observed from bamboos were very high compared to their carbon sequestration potential. Our measurements suggest that bamboos are net emitters of CO₂ during their lifespan.     

Light-induced biophotonic emission from plant tissues

The emission of biophotons in the visible range, following a delay time of 2-200 seconds after exposure to light, has been measured in germinating seeds, roots, flowers, leaves, and cells. It was found that the biophotonic signals are reproducible and light-induced. The observed signals from germinating seeds of Phaseolus aures and decaying leaves of Eucalyptus are presented to show that the signals have characteristic kinetics and intensity. The kinetics of the signal was found to be independent of the stage of growth or decay, though its intensity varied with biological factors. The kinetics in the first minute is characterized by a single exponential decay term while that in the region t ≤ 200 s is characterized by two exponentials. The variation in the intensity of the signal with mass, state of hydration, and growth, and the effect of inhibitors in various systems (e.g. leaves, lichen, Chlorella) are reported.     

Methane emission from living tree wood

The time courses of CO₂, CH₄, and H2 accumulation and O2 absorption at the exposure of trunk wood samples taken from living trees of birch (Betula pendula Roth.), bird cherry tree (Padus avium Mill.), and pine (Pinus sylvestris L.) in the closed volume were studied. The activity of these processes at different temperatures (from 5 to 55°C) was also examined. The main components of gas exchange in all three tree species were O₂ absorption and CO₂ evolution. The fluxes of these gases were equal. In experiments with dehydration-hydration of wood samples, the intrawood origin of “woody” methane was established. Emission of CH₄ and H₂ from the wood depended on temperature. The temperature dependence of CH₄ emission was similar to the temperature dependence of wood respiration. The high correlation between CO₂, CH₄, and H₂ release and O₂ absorption was noted. The relationships between these gas-exchange parameters were not species-specific. Temperature maxima of CH₄ emission and the respiratory activity coincided. This implies that the highest methane emission should be expected in the period of the growth season most favorable for tree physiology. For the wood from all tree species, the ratio between released CH₄ and CO₂ volumes was close to 1: 160. This means that the annual methane emission from living tree is about 2 Mt C, attaining 4% of total methane emission from the territory of North Eurasia. However, taking into account a temperature dependence of methane exchange between the vegetation cover and atmosphere, we can expect that, at global climate warming, methane emission volume might be substantial.     

Methane emission from tidal freshwater marshes

In two tidal freshwater marshes, methane emission,production and accumulation in the pore-water have beenstudied. The two sites differ in their dominantvegetation, i.e., reed and bulrush, and in theirheights above sea level. The reed site was elevated inrelation to the bulrush site and had higher rates ofmethane emission and production. It is argued thatthis difference in methane emission between sites wasprimarily due to a different effect of reed andbulrush plants on methane dynamics rather than methaneoxidation related to tidal elevation. Methane emissionshowed strong seasonality related primarily to plantphysiology and only secondarily to temperature. Twocontrol sites at which vegetation was removedsystematically had lower emission rates indicating anoverall stimulating effect of plants on methaneemission from tidal marshes. Flooding reduced methaneemission, probably by blocking the primary sites ofmethane release in the lower part of the plantstems.     

Bioaerosol emission from wastewater treatment plants

In this report we describe the results of astudy conducted to better estimate airbornemicroorganisms present in wastewater treatmentplants (WWTP) environments. Air samples weretaken with the Air Sampler MAS 100 impactor(Merck) at each stage of an activated-sludgeWWTP (pre-treatment, primary clarifiers,aeration basins and sludge processors), inorder to determine levels of contaminationaccording to work stations. Culture methodswere used to investigate heterotrophic platecount, moulds and yeasts, total and fecalcoliforms, Pseudomonas aeruginosa andspecies belonging to Mycobacteriumtuberculosis complex, whereas these lastmicroorganisms were also analysed by PolymeraseChain Reaction (PCR) methods. Statisticalanalysis showed that pretreatment and primaryclarifiers were the stages with the highestemission of bioaerosols, and that bioaerosolconcentration at each stage depended on windspeed and daily inflow at the WWTP. Lowconcentrations of P. aeruginosa werefound isolated at pretreatment and primaryclarifiers; however, species of M.tuberculosis complex were not detected at anystage of the treatment plant.     

Methane emission from feather moss stands

Data from remote sensing and Eddy towers indicate that forests are not always net sinks for atmospheric CH₄. However, studies describing specific sources within forests and functional analysis of microorganisms on sites with CH₄ turnover are scarce. Feather moss stands were considered to be net sinks for carbon dioxide, but received little attention to their role in CH₄ cycling. Therefore, we investigated methanogenic rates and pathways together with the methanogenic microbial community composition in feather moss stands from temperate and boreal forests. Potential rates of CH₄ emission from intact moss stands (n = 60) under aerobic conditions ranged between 19 and 133 pmol CH₄ h^?1 gdw^?1. Temperature and water content positively influenced CH₄ emission. Methanogenic potentials determined under N₂ atmosphere in darkness ranged between 22 and 157 pmol CH₄ h^?1 gdw^?1. Methane production was strongly inhibited by bromoethane sulfonate or chloroform, showing that CH₄ was of microbial origin. The moss samples tested contained fluorescent microbial cells and between 10⁴ and 10⁵ copies per gram dry weight moss of the mcrA gene coding for a subunit of the methyl CoM reductase. Archaeal 16S rRNA and mcrA gene sequences in the moss stands were characteristic for the archaeal families Methanobacteriaceae and Methanosarcinaceae. The potential methanogenic rates were similar in incubations with and without methyl fluoride, indicating that the CH₄ was produced by the hydrogenotrophic rather than aceticlastic pathway. Consistently, the CH₄ produced was depleted in ¹³C in comparison with the moss biomass carbon and acetate accumulated to rather high concentrations (3–62 mM). The δ¹³C of acetate was similar to that of the moss biomass, indicating acetate production by fermentation. Our study showed that the feather moss stands contained active methanogenic microbial communities producing CH₄ by hydrogenotrophic methanogenesis and causing net emission of CH₄ under ambient conditions, albeit at low rates.