农牧交错区不同植物群落的根冠比特征及土壤呼吸日动态的观测研究

本论文对草地群落地上/地下生物量构成、根冠比特征及其影响因子以及土壤呼吸测定方法比较等的国内外研究进展和主要成果进行了综述，在此基础之上对地处我国北方农牧交错带中段的内蒙古多伦县境内的18种草地群落（包括天然草地和人工草地群落）进行了相关内容的研究工作。 在2002年生长季期间，对这18个植物群落中选取的16个进行了群落学调查，测定了其地上、地下生物量，同时测定了土壤含水量、土壤容重、土壤全氮含量和土壤有机质含量。分别分析了地上、地下生物量以及根冠比（root to shoot ratio）与这些立地因子间的相关关系。同期，从18个群落中选定10个代表性群落测定其土壤呼吸速率，测定方法选用了动态红外气体分析法 (Infra red gas analysis， abbreviated as IRGA)和碱液吸收法（Alkali absorption, abbreviated as AA）。对这两种方法的测定结果进行了比较分析，同时分析了不同群落间土壤呼吸变化与土壤水分和养分状况等的相关关系。主要结论如下： ①16种植物群落的地上和地下生物量差异明显，地上生物量变化范围在80~500 g•m-2之间;相比之下，地下生物量的变化范围要大得多，16个群落中地下生物量最小的为猪毛菜群落，最大的为拂子茅群落，分别为533 g•m-2和2590 g•m-2。群落的根冠比在1.5～11.21之间，平均根冠比为 5.69。 ②土壤含水量对地上和地下生物量有着重要的影响，土壤含水量高的样地（羊草样地）较含水量低（小米蒿样地）的样地地上生物量高，反之亦然。但含水量与地下生物量之间的这种关系却不明显，即土壤含水量高的样地其地下生物量并不一定比含水量低的样地地下生物量高;根冠比与土壤含水量之间基本上呈负相关。土壤全氮含量和有机质含量与地上、地下生物量也存在着一定的正相关关系，而土壤容重却与生物量存有负相关关系;根冠比与土壤全氮、有机质和容重的关系正好与此相反，即根冠比与全氮和有机质含量呈负相关，与容重为正相关。 ③10种植物群落土壤呼吸的昼夜变化比较明显，均为单峰型曲线，主要受土壤温度的驱动，但同时也受到当日降水情况和云量、风速等气象因子的较大影响。因此，影响到这些群落土壤呼吸日动态的一致性，使得规律性并不明显。 ④用碱液吸收法和动态密闭气室法测定的10个群落的土壤呼吸速率变化范围分别为394~894mg C•m-2•d-1和313~2043 mg C•m-2•d-1，其中碱液吸收法测定结果平均为动态气室法的67.5%，明显低于动态密闭气室法。 ⑤两种测定方法具有很好的相关性，R2为0.8739。本研究中发现，在土壤呼吸速率低的情况下，两种方法的测定结果十分接近，甚至碱液吸收法的测定结果稍大于动态密闭气室法;而在土壤呼吸速率较高的情况下，动态密闭气室法测定结果则显著高于碱液吸收法。上述结果与国内外同类研究的结果高度一致，从而为校正我们以往采用碱液吸收法在该区域的测定结果提供了可靠依据。 ⑥各个群落间的土壤呼吸变化与立地土壤水分和土壤养分之间存有一定的相关关系，但并不显著，可能与这些群落土壤呼吸测定不是在同一天进行有关。

黄土高原水蚀风蚀交错带不同土地利用类型土壤呼吸季节变化及其环境驱动

water wind erosion crisscross region; soil respiration rate; seasonal changes; land use pattern; soil temperature; soil moisture; 【摘要】 以黄土高原水蚀风蚀交错区神木县六道沟小流域为研究区,采用动态密闭气室法对植物生长季节(2007年5～10月)5种土地利用方式的土壤呼吸速率进行了测定,并结合水热因子,对不同土地利用方式间土壤呼吸速率的差异性以及其和温度、含水量之间的关系进行了分析。结果表明:5种土地利用类型土壤呼吸速率季节性变化均呈现单峰型曲线,与气温变化趋势一致,其7、8月份土壤呼吸速率均显著高于其它月份(P<0.05);生长季节土壤CO2平均释放速率顺序为:长芒草地>苜蓿地>柠条地>农地>沙柳地,草地在生长前期和旺盛期土壤呼吸强度均显著高于农地和灌木林地;除沙柳地和苜蓿地以外,在土壤呼吸与所有温度指标的关系中,与10cm深度的土壤温度相关性最好,且除沙柳地外,其它4种土地利用类型均与之达到显著相关;农地土壤呼吸对温度的响应最敏感(Q10值为2.20),除沙柳地(Q10值为1.48)外,其它4种土地利用类型Q10值均在2.0左右,接近于全球Q10的平均水平;通过Van’t Hoff模型估算,2007年植物整个生长季节(5～10月份),5种土地利用类型土壤呼吸量从高到低依次为:苜蓿地259gC·m-2,长芒草地236gC·m-2,柠条地226...

Improving the statistical preparation for measuring soil N2O flux by closed chamber

Nitrous oxide emissions from soil are known to be spatially and temporally volatile. Reliable estimation of emissions over a given time and space depends on measuring with sufficient intensity but deciding on the number of measuring stations and the frequency of observation can be vexing. The question of low frequency manual observations providing comparable results to high frequency automated sampling also arises. Data collected from a replicated field experiment was intensively studied with the intention to give some statistically robust guidance on these issues. The experiment had nitrous oxide soil to air flux monitored within 10 m by 2.5 m plots by automated closed chambers under a 3 h average sampling interval and by manual static chambers under a three day average sampling interval over sixty days. Observed trends in flux over time by the static chambers were mostly within the auto chamber bounds of experimental error. Cumulated nitrous oxide emissions as measured by each system were also within error bounds. Under the temporal response pattern in this experiment, no significant loss of information was observed after culling the data to simulate results under various low frequency scenarios. Within the confines of this experiment observations from the manual chambers were not spatially correlated above distances of 1 m. Statistical power was therefore found to improve due to increased replicates per treatment or chambers per replicate. Careful after action review of experimental data can deliver savings for future work.

Calculation of the oxygen isotope discrimination factor for studying plant respiration

Measurement of discrimination against 18O during dark respiration in plants is currently accepted as the only reliable method of estimating the partitioning of electrons between the cytochrome and alternative pathways. In this paper, we review the theory of the technique and its application to a gas-phase system. We extend it to include sampling effects and show that the isotope discrimination factor, D, is calculated as –dln(1 + δ)/dlnO*, where δ is isotopic composition of the substrate oxygen and O*=[O2]/[N2] in a closed chamber containing tissue respiring in the dark. It is not necessary to integrate the expression but, if the integrated form is used, the resultant regression should not be constrained through the origin. This is important since any error in D will have significant effects on the estimation of the flux of electrons through the two pathways.

Microclimate and gas emissions in dairy buildings : Instrumentation, theory and measurements

The aim of this thesis was to develop measurement techniques and systems for measuring air quality and to provide information about air quality conditions and the amount of gaseous emissions from semi-insulated and uninsulated dairy buildings in Finland and Estonia. Specialization and intensification in livestock farming, such as in dairy production, is usually accompanied by an increase in concentrated environmental emissions. In addition to high moisture, the presence of dust and corrosive gases, and widely varying gas concentrations in dairy buildings, Finland and Estonia experience winter temperatures reaching below -40 ºC and summer temperatures above +30 ºC. The adaptation of new technologies for long-term air quality monitoring and measurement remains relatively uncommon in dairy buildings because the construction and maintenance of accurate monitoring systems for long-term use are too expensive for the average dairy farmer to afford. Though the documentation of accurate air quality measurement systems intended mainly for research purposes have been made in the past, standardised methods and the documentation of affordable systems and simple methods for performing air quality and emissions measurements in dairy buildings are unavailable. In this study, we built three measurement systems: 1) a Stationary system with integrated affordable sensors for on-site measurements, 2) a Wireless system with affordable sensors for off-site measurements, and 3) a Mobile system consisting of expensive and accurate sensors for measuring air quality. In addition to assessing existing methods, we developed simplified methods for measuring ventilation and emission rates in dairy buildings. The three measurement systems were successfully used to measure air quality in uninsulated, semi-insulated, and fully-insulated dairy buildings between the years 2005 and 2007. When carefully calibrated, the affordable sensors in the systems gave reasonably accurate readings. The spatial air quality survey showed high variation in microclimate conditions in the dairy buildings measured. The average indoor air concentration for carbon dioxide was 950 ppm, for ammonia 5 ppm, for methane 48 ppm, for relative humidity 70%, and for inside air velocity 0.2 m/s. The average winter and summer indoor temperatures during the measurement period were -7º C and +24 ºC for the uninsulated, +3 ºC and +20 ºC for the semi-insulated and +10 ºC and +25 ºC for the fully-insulated dairy buildings. The measurement results showed that the uninsulated dairy buildings had lower indoor gas concentrations and emissions compared to fully insulated buildings. Although occasionally exceeded, the ventilation rates and average indoor air quality in the dairy buildings were largely within recommended limits. We assessed the traditional heat balance, moisture balance, carbon dioxide balance and direct airflow methods for estimating ventilation rates. The direct velocity measurement for the estimation of ventilation rate proved to be impractical for naturally ventilated buildings. Two methods were developed for estimating ventilation rates. The first method is applicable in buildings in which the ventilation can be stopped or completely closed. The second method is useful in naturally ventilated buildings with large openings and high ventilation rates where spatial gas concentrations are heterogeneously distributed. The two traditional methods (carbon dioxide and methane balances), and two newly developed methods (theoretical modelling using Fick s law and boundary layer theory, and the recirculation flux-chamber technique) were used to estimate ammonia emissions from the dairy buildings. Using the traditional carbon dioxide balance method, ammonia emissions per cow from the dairy buildings ranged from 7 g day-1 to 35 g day-1, and methane emissions per cow ranged from 96 g day-1 to 348 g day-1. The developed methods proved to be as equally accurate as the traditional methods. Variation between the mean emissions estimated with the traditional and the developed methods was less than 20%. The developed modelling procedure provided sound framework for examining the impact of production systems on ammonia emissions in dairy buildings.

Hydrogen soil deposition and atmospheric variations in the boreal zone

This research has been prompted by an interest in the atmospheric processes of hydrogen. The sources and sinks of hydrogen are important to know, particularly if hydrogen becomes more common as a replacement for fossil fuel in combustion. Hydrogen deposition velocities (vd) were estimated by applying chamber measurements, a radon tracer method and a two-dimensional model. These three approaches were compared with each other to discover the factors affecting the soil uptake rate. A static-closed chamber technique was introduced to determine the hydrogen deposition velocity values in an urban park in Helsinki, and at a rural site at Loppi. A three-day chamber campaign to carry out soil uptake estimation was held at a remote site at Pallas in 2007 and 2008. The atmospheric mixing ratio of molecular hydrogen has also been measured by a continuous method in Helsinki in 2007 - 2008 and at Pallas from 2006 onwards. The mean vd values measured in the chamber experiments in Helsinki and Loppi were between 0.0 and 0.7 mm s-1. The ranges of the results with the radon tracer method and the two-dimensional model were 0.13 - 0.93 mm s-1 and 0.12 - 0.61 mm s-1, respectively, in Helsinki. The vd values in the three-day campaign at Pallas were 0.06 - 0.52 mm s-1 (chamber) and 0.18 - 0.52 mm s-1 (radon tracer method and two-dimensional model). At Kumpula, the radon tracer method and the chamber measurements produced higher vd values than the two-dimensional model. The results of all three methods were close to each other between November and April, except for the chamber results from January to March, while the soil was frozen. The hydrogen deposition velocity values of all three methods were compared with one-week cumulative rain sums. Precipitation increases the soil moisture, which decreases the soil uptake rate. The measurements made in snow seasons showed that a thick snow layer also hindered gas diffusion, lowering the vd values. The H2 vd values were compared to the snow depth. A decaying exponential fit was obtained as a result. During a prolonged drought in summer 2006, soil moisture values were lower than in other summer months between 2005 and 2008. Such conditions were prevailing in summer 2006 when high chamber vd values were measured. The mixing ratio of molecular hydrogen has a seasonal variation. The lowest atmospheric mixing ratios were found in the late autumn when high deposition velocity values were still being measured. The carbon monoxide (CO) mixing ratio was also measured. Hydrogen and carbon monoxide are highly correlated in an urban environment, due to the emissions originating from traffic. After correction for the soil deposition of H2, the slope was 0.49±0.07 ppb (H2) / ppb (CO). Using the corrected hydrogen-to-carbon-monoxide ratio, the total hydrogen load emitted by Helsinki traffic in 2007 was 261 t (H2) a-1. Hydrogen, methane and carbon monoxide are connected with each other through the atmospheric methane oxidation process, in which formaldehyde is produced as an important intermediate. The photochemical degradation of formaldehyde produces hydrogen and carbon monoxide as end products. Examination of back-trajectories revealed long-range transportation of carbon monoxide and methane. The trajectories can be grouped by applying cluster and source analysis methods. Thus natural and anthropogenic emission sources can be separated by analyzing trajectory clusters.

Monitoring charged particle and ion emissions from a laser printer

While the emission rate of ultrafine particles has been measured and quantified, there is very little information on the emission rates of ions and charged particles from laser printers. This paper describes a methodology that can be adopted for measuring the surface charge density on printed paper and the ion and charged particle emissions during operation of a high-emitting laser printer and shows how emission rates of ultrafine particles, ions and charged particles may be quantified using a controlled experiment within a closed chamber.

Optimising the cell source and biomaterials for the generation of vascularized adipose tissue in vivo

We initially described a rat chamber model with an inserted arteriovenous pedicle which spontaneously generates 3-dimensional vascularized connective tissue (Tanaka Y et al., Br J Plast Surg 2000; 53: 51-7). More recently we have developed a murine chamber model containing reconstituted basement membrane (Matrigel®) and FGF-2 that generates vascularized adipose tissue in vivo (Cronin K et al., Plast Reconstr Surg 2004; in press). We have extended this work to assess the cellular and matrix requirements for the Matrigel®- induced neo-adipogenesis. We found that chambers sealed to host fat were unable to grow new adipose tissue. In these chambers the Matrigel® became vascularized with maximal outgrowth of vessels extending to the periphery at 6 weeks. A small amount of adipose tissue was found adjacent to the vessels, most likely arising from periadventitial adipose tissue. In contrast, chambers open to interaction with endogenous adipose tissue showed abundant new fat, and partial exposure to adjacent adipose tissue clearly showed neo-adipogenesis only in this area. Addition of small amounts of free fat to the closed chamber containing Matrigel® was able to induce neo-adipogenesis. Addition of small pieces of human fat also caused neo-adipogenesis in immunocompromised (SCID) mice. Also, we found Matrigel® to induce adipogenesis of Lac-Z-tagged (Rosa-26) murine bone marrow-derived mesenchymal stem cells, and cells similar to these have been isolated from human adipose tissue. Given that Matrigel® is a mouse product and cannot be used in humans, we have started investigating alternative matrix scaffolds for adipogenesis such as the PDA-approved PLGA, collagen and purified components derived from Matrigel®, such as laminin-1. The optimal conditions for adipogenesis with these matrices are still being elucidated. In conclusion, we have demonstrated that a precursor cell source inside the chamber is essential for the generation of vascularized adipose tissue in vivo. This technique offers unique potential for the reconstruction of soft tissue defects and may enable the generation of site-specific tissue using the correct microenvironment.

Use of wetland buffer areas to reduce nitrogen transport from forested catchments: Retention capacity, emissions of N2O and CH4 and vegetation composition dynamics

The use of buffer areas in forested catchments has been actively researched during the last 15 years; but until now, the research has mainly concentrated on the reduction of sediment and phosphorus loads, instead of nitrogen (N). The aim of this thesis was to examine the use of wetland buffer areas to reduce the nitrogen transport in forested catchments and to investigate the environmental impacts involved in their use. Besides the retention capacity, particular attention was paid to the main factors contributing to the N retention, the potential for increased N2O emissions after large N loading, the effects of peatland restoration for use as buffer areas on CH4 emissions, as well as the vegetation composition dynamics induced by the use of peatlands as buffer areas. To study the capacity of buffer areas to reduce N transport in forested catchments, we first used large artificial loadings of N, and then studied the capacity of buffer areas to reduce ammonium (NH4-N) export originating from ditch network maintenance areas in forested catchments. The potential for increased N2O emissions were studied using the closed chamber technique and a large artificial N loading at five buffer areas. Sampling for CH4 emissions and methane-cycling microbial populations were done on three restored buffer areas and on three buffers constructed on natural peatlands. Vegetation composition dynamics was studied at three buffer areas between 1996 and 2009. Wetland buffer areas were efficient in retaining inorganic N from inflow. The key factors contributing to the retention were the size and the length of the buffer, the hydrological loading and the rate of nutrient loading. Our results show that although the N2O emissions may increase temporarily to very high levels after a large N loading into the buffer area, the buffer areas in forested catchments should be viewed as insignificant sources of N2O. CH4 fluxes were substantially higher from buffers constructed on natural peatlands than from the restored buffer areas, probably because of the slow recovery of methanogens after restoration. The use of peatlands as buffer areas was followed by clear changes in plant species composition and the largest changes occurred in the upstream parts of the buffer areas and the wet lawn-level surfaces, where the contact between the vegetation and the through-flow waters was closer than for the downstream parts and dry hummock sites. The changes in the plant species composition may be an undesired phenomenon especially in the case of the mires representing endangered mire site types, and therefore the construction of new buffer areas should be primarily directed into drained peatland areas.

Emissão de CO2 do solo e sua correlação com a rizosfera de diferentes paisagens de áreas mineradas do município de Santo Antônio de Pádua-RJ

Objetivando avaliar o comportamento das emissões de CO2 do solo em áreas mineradas do município de Santo Antônio de Pádua-RJ e sua correlação com a rizosfera, este presente estudo utilizou uma câmara fechada com sensor de infravermelho em três diferentes paisagens, a saber: A-1 (área reflorestada há 10 anos), A-2 (área desmatada) e A-3 (área em processo de recuperação). Em cada área foi instalada três cilindros para efeitos de repetição. O monitoramento foi realizado durante os meses representativos de cada estação do ano de 2013, sendo a análise realizada durante dois dias consecutivos. Concomitantemente as coletas de CO2 foram realizadas coletas de dados de temperatura e umidade do solo, sendo também avaliadas informações pedológicas através das análises de granulometria, porosidade, pH, carbono orgânico e matéria orgânica. Informações meteorológicas e microclimatológicas também foram extraídas através de uma estação meteorológica automática e através de sensores portáteis. Os resultados permitem concluir que existe uma variação sazonal dos fluxos de CO2, havendo uma tendência de máximos de emissão durante o verão e de mínimas durante o inverno, sendo o outono e a primavera marcados por valores medianos. A correlação das áreas entre os dois dias monitoramento indicam que as emissões foram semelhantes ao da análise em dia anterior, apresentando uma correlação significativa a 5% para A-1 e A-2 e de 1% para A-3. A-1 e A-2 apresentaram emissões de CO2 mais homogêneas que A-3, havendo, entretanto, um maior fluxo de CO2 durante o verão para todas as áreas. Os dados de MOS, COS e pH demonstraram não haver uma correlação direta com as emissões de CO2. Os dados de porosidade e densidade, porém, apontam para uma possível correlação com as menores emissões de CO2 em A-3 devido a menor porosidade e maior densidade de seus solos. A temperatura do solo foi a variável que mais se correlacionou com as emissões de CO2, havendo um índice igual a r =0,68 para A-1 e de r =0,74 para A-2, sendo que em A-3 esta correlação não foi significativa. A temperatura do ar demonstrou uma correlação somente na área descampada de A-2. No que se refere à correlação da umidade do solo não houve correlações diretas significativas, sendo que somente houve uma correlação negativa (r=-0,50) significativa a 5% em A-3 com a umidade do ar. O diagnóstico ambiental das áreas de monitoramento revela que estas possuem baixos indicadores de qualidade, sendo afetados também pela escassez hídrica da região durante oito meses do ano. A-1 apresenta os melhores indicadores biológicos, químicos e microclimáticos, seguidos por A-2 e A-3 que apresentam diversas deficiências e problemas em termos de estrutura e atividade biológica dos solos. Neste estudo permite-se concluir que áreas próximas, porém com características distintas podem produzir diferentes padrões de emissão de CO2, dificultando, portanto, estimativas globais de emissão de CO2. Os elementos mais associados às emissões de CO2 parecem estar relacionados à temperatura do solo e do ar, umidade do ar e estrutura do solo, havendo, entretanto, outros fatores que podem estar indiretamente relacionados e que exercem diferentes influências de acordo com o ambiente analisado.

静态箱-气相色谱法研究人类活动对内蒙古草原主要温室气体交换通量的影响

本研究全面分析了陆地生态系统主要温室气体N2O、CO2和CH4通量研究的主要方法，系统阐述了改进后的静态箱-气相色谱法观测内蒙古半干旱原N2O、CO2和CH4交换通量的具体应用。就用此观测系统，于1998年5月至2000年2月长期定位观测研究了内蒙古锡林河流域主要人类活动（放牧、家垦）对N2O、CO2和CH4交换通量强度及季节变化的影响，同时对水分、地温等相关因素的影响作了初步探讨。 通过对主要温室气体N2O、CO2和CH4通量观测主要方法的比较分析认为：静态箱-气相色谱法是观测内蒙古半干旱草原N2O、CO2和CH4交换通量行之有效的方法，改进后的观测系统其准确性和再现性基本可以满足研究要求，但箱法的局限性也导致对CO2及不同牧压下草原N2O通量的观测很难得到客观准确的结果。 农垦对内蒙古草甸草原N2O、CO2和CH4通量有着重要的影响：农垦显著增大了草甸草原N2O排放通量，但对N2O排放通量的季节变化无显著影响;在植物生长旺期之前，农垦对草甸草原CO2排放通量无显著影响，在植物生长旺期及之后的小麦成熟期，农垦明显增大了CO2的排放。农垦还使得CO2排放通量的季节变化由单峰型变为双峰型;农垦对CH4通量的强度及季节变化均无显著影响。 连续两年的观测结果表明，研究放牧对内蒙古典型草原CO2和CH4通量的影响应结合水分条件来考虑。不同牧压下冷蒿-小禾草草原CO2排放能量受水分条件的显著影响，水分条件改变了CO2通量的季节变化。丰水年CO2排放强度随着放牧强度的增大而增大，正常年份放牧强度对CO2排放通量强度无显著影响。两年的观测均发现不同的放牧强度对CO2通量的季节变化没有影响;土壤-植被系统吸收CH4的能力在不同放牧强度处理之间没有显著差异，而同一放牧率下年际间CH4通量变化很大，正常年份比丰水年吸收通量大。同时分析了温度与不同放牧强度草原CH4通量的关系，认为影响放牧条件下冷蒿-不禾草草原CH4吸收通量的主要因子是地表以下10cm土壤温度。

Comparative study on CO2 emissions from different types of alpine meadows during grass exuberance period

Potentilla fruticosa scrub, Kobresia humilis meadow and Kobresia tibetica meadow are widely distributed on the Qinghai-Tibet Plateau. During the grass exuberance period from 3 July to 4September, based on close chamber-GC method, a study on CO2 emissions from different treatments was conducted in these meadows at Haibei research station, CAS. Results indicated that mean CO2emission rates from various treatments were 672.09+152.37 mgm-2h-1 for FC (grass treatment); 425.41+191.99 mgrn-2h-1 for FJ (grass exclusion treatment); 280.36+174.83 mgrn-2h-1 for FL (grass and roots exclusion treatment); 838.95+237.02 mgm-2h-1 for GG (scrub+grass treatment); 528.48+205.67 mgm-2h-1for GC (grass treatment); 268.97 ±99.72 mgm-2h-1 for GL (grass and roots exclusion treatment); and 659.20±94.83 mgm-2h-1 for LC (grass treatment), respectively (FC, FJ, FL, GG, GC, GL, LC were the Chinese abbreviation for various treatments). Furthermore, Kobresia humilis meadow, Potentilla fruticosa scrub meadow and Kobresia tibetica meadow differed greatly in average CO2 emission rate of soil-plant system, in the order of GG＞FC＞LC＞GC. Moreover, in Kobresia humilis meadow,heterotrophic and autotrophic respiration accounted for 42% and 58% of the total respiration of soil-plant system respectively, whereas, in Potentilla fruticosa scrub meadow, heterotrophic and autotrophic respiration accounted for 32% and 68% of total system respiration from G-G; 49% and 51%from GC. In addition, root respiration from Kobresia humilis meadow approximated 145 mgCO2m-2h-1,contributed 34% to soil respiration. During the experiment period, Kobresia humilis meadow and Potentilla fruticosa scrub meadow had a net carbon fixation of 111.11 grn-2 and 243.89 grn-2,respectively. Results also showed that soil temperature was the main factor which influenced CO2 emission from alpine meadow ecosystem, significant correlations were found between soil temperature at 5 cm depth and CO2 emission from GG, GC, FC and FJ treatments. In addition, soil moisture may be the inhibitory factor of CO2 emission from Kobresia tibetica meadow, and more detailed analyses should be done in further research.

Methane emissions by alpine plant communities in the Qinghai-Tibet Plateau

For the first time to our knowledge, we report here methane emissions by plant communities in alpine ecosystems in the Qinghai-Tibet Plateau. This has been achieved through long-term field observations from June 2003 to July 2006 using a closed chamber technique. Strong methane emission at the rate of 26.2 +/- 1.2 and 7.8 +/- 1.1 mu g CH4 m(-2) h(-1) was observed for a grass community in a Kobresia humilis meadow and a Potentilla fruticosa meadow, respectively. A shrub community in the Potentilla meadow consumed atmospheric methane at the rate of 5.8 +/- 1.3 mu g CH4 m(-2) h(-1) on a regional basis; plants from alpine meadows contribute at least 0.13 Tg CH4 yr(-1) in the Tibetan Plateau. This finding has important implications with regard to the regional methane budget and species-level difference should be considered when assessing methane emissions by plants.

Short-term effects of sheep excrement on carbon dioxide, nitrous oxide and methane fluxes in typical grassland of Inner Mongolia

Excrement patches of grazing animals play an important role in greenhouse gas (GHG) fluxes due to the high nitrogen (N) and available carbon (C) deposited in small areas, but little information is available for the effect of excrement in the Inner Mongolian grassland (43 26 degrees N, 116 degrees 40'E). To elucidate the effect of grazing sheep urine, fresh dung and compost on fluxes of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O), a short-term field study (65 days) was carried out in the typical grassland of Inner Mongolia with the optimised closed chamber/GC technique. Compared with the control, cumulative net CH4 consumption decreased 36, 31, and 18% from urine, fresh dung, and compost plots, respectively; net CO2-C output increased by 6.5, 1.5, and 1.2% from urine, fresh dung, and compost treated soil, respectively; about three times as much N2O-N was emitted from urine and the fresh dung treatments during 65 days. Nitrous oxide emission was positively correlated with CO, emission (R = 0.691, P < 0.01) and water-filled pore space (R = 0.698, P < 0.01). The percentages of N2O-N loss of applied-N were 0.44 and 1.05% for urine and fresh dung, respectively. Our results suggest that in autumn in the degraded grassland of Inner Mongolia, the effect of sheep excrement may be ignored when evaluating the total GHG emissions.