高寒草甸土壤有机碳储量和CO2通量

选择青藏高原东北隅海北站区的4种高寒草甸土壤进行高分辨率采样，测定土壤有机碳及其^14C信号；应用^14C示踪技术探讨高寒草甸土壤有机碳更新周期和CO2通量．研究得出海北站高寒草甸生态系统土壤有机碳储量在22．12×10^4～30．75×10^4kgC•hm^-2之间，平均为26．86×10^4kgC•hm^2．高寒草甸土壤有机碳的更新周期从表层的45～73a随深度增加到数百年甚至数千年或更长．高寒草甸生态系统土壤呼吸的CO2通量变化于103．24—254．93gC•m^-2•a^-1之间，平均为191．23gC•m^-2•a^-1．土壤有机质分解产生的CO2通量变化于73．3～181gC•m^-2•a^-1之间．矮嵩草草甸土壤30％以上的有机碳贮存在土壤表层（0～10cm）的活动碳库中，土壤有机质更新产生的CO2占整个剖面有机质更新产生的CO2通量的72．8％～81．23％．响应于全球变暖，青藏高原高寒草甸生态系统土壤有机碳的储量、流量、归宿变化等问题有待进一步研究．

草毡寒冻雏形土有机质补给、分解及大气CO2通量交换

调查草毡寒冻雏形土生物量及土壤有机质,利用涡度相关技术观测该区域作用层与大气CO2通量.结果表明：地下90%生物量集中于0～10 cm的表土层,年总净初级生产量约935.0 g/m2;土壤有机质含量在6.401～7.060%之间;净CO2通量呈明显的日变化和季节变化规律;5月中旬到9月底为CO2的净吸收（780 g CO2/m2）,其中以7月最高,净吸收量明显高于非生长季的,10月到翌年5月初CO2的净排放量（383 g CO2/m2）;全年固定碳高达397 g/m2.

青藏高原矮嵩草草甸和金露梅灌丛草甸CO2通量变化与环境因子的关系

利用涡度相关技术观测了青藏高原两个典型的生态系统即矮嵩草（Kobresia humilis）草甸和金露梅（Potentilla fruticosa）灌丛草甸的CO2通量，并就2003年8月份的数据，分析了生态系统通量变化与环境因子的关系。8月份是这两个生态系统的叶面积指数达到最高也是相对稳定的时期，在此期间矮嵩草草甸和金露梅灌丛草甸净碳吸收量分别达56．2和32．6g C•m^-2，日CO2吸收量最大值分别为12．7μmol•m^-2•s^-1和9．3μmol•m^-2•s^-1，排放量最大值分别为5．1μmol•m^-2•s^-1和5．7μmol•m^-2•s^-1。在相同光合有效光量子通量密度（PPFD）条件下，矮嵩草草甸CO2吸收速度大于金露梅灌丛草甸；在PPFD高于1200μmol•m^-2•s^-1。的条件下，随气温增加，两生态系统的CO2吸收速度都下降，但矮嵩草草甸的下降速度（-0．086）比金露梅灌丛草甸（-0．016）快。土壤水分影响土壤呼吸，并且影响差异因植被类型不同而不同。生态系统日CO2吸收量随昼夜温差增加而增大；较大的昼夜温差导致较高的净CO2交换量；植物反射率与CO2通量之间存在负相关关系。

高寒灌丛草甸生态系统CO2释放的初步研究

以金露梅(Potentilla fruticosa)灌丛草甸生态系统为对象，应用静态密闭箱-气相色谱法对高寒灌丛(GG)、丛内草甸(GC)和裸地(GL)的CO2释放进行了初步研究。结果表明：GG、GC和GL CO2的释放速率均呈明显的单峰型日变化进程，最大释放速率出现在15：00～17：00之间，最小值在7：00前后出现，白天释放速率大于夜晚；CO2释放速率具有明显的季节性变化特征，生长期CO2释放速率明显高于枯黄期，且均表现为正排放，8月为CO2释放高峰期，释放速率GG>GC>GL(P<0．01)；2003年6月30日至2004年2月28日，高寒灌丛植被-土壤系统CO2释放量为3088．458±287．02g／m^2，丛内草甸植被-土壤系统CO2释放量为2239．685±183．68g／m^2，其中基础土壤呼吸CO2的释放量约为1346．748±176．24g／m^2，分别占GG和GC释放量的43．61％和60．13％；CO2释放速率的日变化主要受地表和5cm地温制约，而季节动态与5cm地温呈显著正相关关系(P<0．01)。

海北高寒灌丛草甸生态系统CO2释放速率的季节变化规律

在中国科学院海北高寒草甸生态系统定位站干柴滩地区以金露梅Potentilla fruticosa灌丛草甸生态系统为研究对象,应用静态密闭箱-气相色谱法对高寒灌丛(GG)、丛内草甸(GC)和次生裸地(GL)的CO2释放速率进行了长期观测,并对年释放量作了初步估测.结果表明,GG,GC和GL CO2的释放速率在一年内有明显的季节变化.植物生长季CO2释放量明显高于枯黄期,释放速率GG>GC>GL(P＜0.01),且均表现为正排放.不同季节CO2释放存在明显差异,表现为夏季＞秋季＞春季＞冬季.2003年6月30日至2004年6月28日,高寒灌丛植被-土壤系统CO2释放量为4 293.63±955.75 g/m2,丛内草甸植被-土壤系统CO2释放量为3 319.68±806.19 g/m2,裸地CO2的释放量为1 724.14±444.14 g/m2.CO2释放速率的季节变化与土壤5 cm温度呈显著正相关关系(P＜0.01).

积雪对藏北高寒草甸CO2和水汽通量的影响

于2002和2003年冬季运用涡度相关法测定藏北草甸在有积雪和无雪条件下的CO2和水汽通量.结果表明:在同一层次CO2浓度,在有雪时CO2浓度低于无雪时,其中只有20 cm和160 cm层次间差异极显著(P＜0.01);在同一层次,前者的水汽浓度极显著地高于后者(P＜0.01);积雪时,CO2通量与5 cm土温相关不显著;高寒草甸CO2交换量,随着积雪时间的延长呈线性降低,而高寒灌丛和沼泽则相反;沼泽和草甸在有雪时,CO2通量值极显著高于无雪时(P＜0.01),而灌丛在这两个条件下CO2通量值之间差异不显著.

青藏高原3种植被类型净生态系统CO2交换量的比较

采用涡度相关观测技术系统, 于2003年7月1日～2004年6月30日对青藏高原高寒草甸3种植被类型(矮嵩草草甸、金露梅灌丛草甸和藏嵩草沼泽化草甸)生态系统CO2通量进行观测和分析. 结果表明, 嵩草草甸、灌丛草甸和沼泽化草甸CO2最大吸收率分别为16.78, 10.42和16.57 mmol/m2•s; 最大CO2排放率分别为8.22, 7.73和18.67 mmol/m2•s; 嵩草草甸和灌丛草甸一年从大气中分别吸收CO2 282和53 g/m2, 而沼泽草甸一年向大气排放CO2 478 g/m2. 证明青藏高原嵩草草甸和灌丛草甸比C4草原和一些低海拔草原和森林具有一个较低CO2吸收和排放量潜能, 而沼泽化草甸具有一个较高的排放潜能, 揭示了青藏高原高寒草甸生态系统不同植被类型的碳源/汇的明显差异, 主要是由植物光合能力不同和土壤呼吸差异引起的.

青藏高原高寒灌丛CO2通量日和月变化特征

采用涡度相关法对青藏高原高寒灌丛CO2通量进行连续观测的结果表明,青藏高原高寒灌丛CO2通量呈明显的日和月变化特征.就日变化而言,暖季(7月)CO2通量峰值出现在12:00左右(-1.19 g CO2/(m2•h)-1),08:00～19:00时CO2净吸收,而20:00～07:00为CO2净排放; 冷季(1月)CO2通量变化振幅极小,除11:00～17:00时少量的CO2净排放以外(0.11 g CO2/(m2•h)-1左右),其余时段CO2通量接近于零.从月变化来看,6～9月为CO2净吸收阶段,8月CO2净吸收最大,6～9月CO2净吸收的总量达673 g CO2/m2; 1～5月及10～12月为CO2净排放,共排放446 g CO2/m2,4月CO2净排放最大.全年CO2通量核算表明,无放牧条件下青藏高原高寒灌丛是显著的CO2汇,全年CO2净吸收量达227 g CO2/m2.

Monitoring and simulation of water, heat,and CO2 fluxes in terrestrial ecosystems based on the APEIS-FLUX system

The Integrated Environmental Monitoring (IEM) project, part of the Asia-Pacific Environmental Innovation Strategy (APEIS) project, developed an integrated environmental monitoring system that can be used to detect, monitor, and assess environmental disasters, degradation, and their impacts in the Asia-Pacific region. The system primarily employs data from the moderate resolution imaging spectrometer (MODIS) sensor on the Earth Observation System- (EOS-) Terra/Aqua satellite,as well as those from ground observations at five sites in different ecological systems in China. From the preliminary data analysis on both annual and daily variations of water, heat and CO2 fluxes, we can confirm that this system basically has been working well. The results show that both latent flux and CO2 flux are much greater in the crop field than those in the grassland and the saline desert, whereas the sensible heat flux shows the opposite trend. Different data products from MODIS have very different correspondence, e.g. MODIS-derived land surface temperature has a close correlation with measured ones, but LAI and NPP are quite different from ground measurements, which suggests that the algorithms used to process MODIS data need to be revised by using the local dataset. We are now using the APEIS-FLUX data to develop an integrated model, which can simulate the regional water,heat, and carbon fluxes. Finally, we are expected to use this model to develop more precise high-order MODIS products in Asia-Pacific region.

矮嵩草草甸植被-土壤系统CO2的释放特征

采用静态箱-气相色谱法,对高寒矮嵩草草甸植被-土壤系统CO2释放特征研究结果表明:3个处理(FC、FJ、FL)CO2释放速率具有明显的日变化规律,日最大释放速率出现在13:00左右,最小释放速率在4:00前后,且白天的释放速率均大于夜间;CO2释放速率也具有明显的季节变化特征,植物生长期释放速率明显高于枯黄期,且均表现为正排放;在整个观测期间(6月30日～1月28日)CO2平均释放速率依次为FC>FJ>FL,矮嵩草草甸植物-土壤系统CO2释放速率为438.34±264.12mg/(m2•h)(FC),土壤呼吸速率为313.20±189.74 mg/(m2•h)(FJ),土壤微生物呼吸速率为230.34±145.46mg/(m2•h)(FL),植物根系呼吸占土壤呼吸的26.5%.植物、植物根系以及土壤微生物CO2释放速率与土壤5 cm温度呈极显著正相关关系,相关系数分别为0.858、0.628和0.672(P<0.01).整个系统呼吸、土壤呼吸与土壤5 cm温度可拟和为一指数方程,方程为y=168.03e0.10x86x(R2=0.8783)和y=149.69e0.0745x(R2=0.8189).

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.

植物生长季退化草毡寒冻雏形土CO2释放特征

对中国科学院海北高寒草甸生态系统定位站地区退化草毡寒冻雏形土CO2释放的全天候连续观测结果表明，退化草毡寒冻雏形土CO2的释放有明显的日变化和季节动态，日最大释放速率出现于12：00-14：00，最小释放速率出现于6：00-8：00；植物生长季的最大振幅为462.49mg·m^-2·h^-1（8月18日），最小振幅为114.97mg·m^-2·h^-1（5月9日），CO2释放速率白天大于夜晚。不同物候期CO2释放速率亦不同，草盛期>枯黄期>青期。最大日均值为480.76mg·m^-2·h^-1（8月18日），最小日均值为140.77mg·m^-2·h^-1（5月9日）。释放速率与气温、地表温度及土壤5cm地温均呈显著或极显著相关关系，表明温度是决定CO2释放速率季节变化的首要因素。

Soil organic carbon storage and soil CO2 flux in the alpine meadow ecosystem

High-resolution sampling, measurements of organic carbon contents and C-14 signatures of selected four soil profiles in the Haibei Station situated on the northeast Tibetan Plateau, and application of C-14 tracing technology were conducted in an attempt to investigate the turnover times of soil organic carbon and the soil-CO2 flux in the alpine meadow ecosystem. The results show that the organic carbon stored in the soils varies from 22.12x10(4) kg C hm(-2) to 30.75x10(4) kg C hm(-2) in the alpine meadow ecosystems, with an average of 26.86x10(4) kg C hm(-2). Turnover times of organic carbon pools increase with depth from 45 a to 73 a in the surface soil horizon to hundreds of years or millennia or even longer at the deep soil horizons in the alpine meadow ecosystems. The soil-CO2 flux ranges from 103.24 g C m(-2) a(-1) to 254.93 gC m(-2) a(-1), with an average of 191.23 g C m(-2) a(-1). The CO2 efflux produced from microbial decomposition of organic matter varies from 73.3 g C m(-2) a(-1) to 181 g C m(-2) a(-1). More than 30% of total soil organic carbon resides in the active carbon pool and 72.8%. 81.23% of total CO2 emitted from organic matter decomposition results from the topsoil horizon (from 0 cm to 10 cm) for the Kobresia meadow. Responding to global warming, the storage, volume of flow and fate of the soil organic carbon in the alpine meadow ecosystem of the Tibetan Plateau will be changed, which needs further research.

Modeling gross primary production of alpine ecosystems in the Tibetan Plateau using MODIS images and climate data

The eddy covariance technique provides measurements of net ecosystem exchange (NEE) Of CO2 between the atmosphere and terrestrial ecosystems, which is widely used to estimate ecosystem respiration and gross primary production (GPP) at a number Of CO2 eddy flux tower sites. In this paper, canopy-level maximum light use efficiency, a key parameter in the satellite-based Vegetation Photosynthesis Model (VPM), was estimated by using the observed CO2 flux data and photosynthetically active radiation (PAR) data from eddy flux tower sites in an alpine swamp ecosystem, an alpine shrub ecosystem and an alpine meadow ecosystem in Qinghai-Tibetan Plateau, China. The VPM model uses two improved vegetation indices (Enhanced Vegetation Index (EVI), Land Surface Water Index (LSWI)) derived from the Moderate Resolution Imaging Spectral radiometer (MODIS) data and climate data at the flux tower sites, and estimated the seasonal dynamics of GPP of the three alpine grassland ecosystems in Qinghai-Tibetan Plateau. The seasonal dynamics of GPP predicted by the VPM model agreed well with estimated GPP from eddy flux towers. These results demonstrated the potential of the satellite-driven VPM model for scaling-up GPP of alpine grassland ecosystems, a key component for the study of the carbon cycle at regional and global scales. (c) 2006 Elsevier Inc. All rights reserved.

CO2 fluxes of alpine shrubland ecosystem on the north-eastern Tibetan plateau

We measured ecosystem CO2 fluxes for an alpine shrubland on the north-eastern Tibetan Plateau, Qinghai, China. The study is to understand (1) the seasonal variation of CO2 flux and (2) how environmental factors affect the seasonality of CO2 exchange in the alpine ecosystem. Daytime ecosystem respiration was extrapolated from the relationship between temperature and nighttime CO2 fluxes under high turbulent conditions.Seasonal patterns of gross ecosystem production, ecosystem respiration and net ecosystem CO2 exchange followed highly the seasonal change of aboveground biomass in the alpine shrubland. The net ecosystem CO2 exchange was mainly controlled by the variation of photosynthetic photon flux density, while the ecosystem respiration was closely correlated to the soil temperature at 5-cm depth. Integrated values of gross ecosystem production, ecosystem respiration and net ecosystem CO2 exchange for the period from November 1, 2002 to October 31 2003 were estimated to be 1418, 1155 and 222 g CO2 m(-2) yr(-1), respectively.