Characteristics of net ecosystem carbon dioxide exchange(NEE) from August to October of Alpine meadow on the Tibetan Plateau,China

The Alpine meadow is one of the vegetation types widely distributed on the Tibetan Plateau in China with an area of about 1.2 million square kilometers.The Damxung rangeland station,located in the hinterland of the Tibetan Plateau,is covered with an typical vegetation.The continuous carbon flux data (from August to middle October,2003) measured with the open-path eddy covariance system was used to analyze the diurnal variation pattern of net ecosystem carbon dioxide exchange (NEE) and its relationship with the environmental factors,such as photosynthetically active radiation (PAR),precipitation,and temperature.Results showed that NEE presented obvious diurnal variation pattern with single-peak of diurnal maximum carbon assimilation at 11:00-12:00 (local time) with an CO2.m-2-s-1.During the daytime,NEE fitted fairly well with PAR in a rectangular hyperbola function with the apparent the night-time,NEE showed a good exponential relation with the soil temperature at 5 cm depth.     

青藏高原高寒草甸生态系统净二氧化碳交换量特征

高寒草甸是青藏高原广泛分布的植被类型之一,面积约120万km2,地处青藏高原腹地的当雄草原站即位于该类植被的典型分布区。以2003年8~10月中旬在该站用涡度相关法连续观测的CO2通量数据资料为基础,分析了高寒草甸生态系统8~10月份净二氧化碳交换量(NEE)的日变化规律,及其与光合有效辐射、降水、温度等环境因子之间的关系。结果表明,8~10月份的日均NEE有明显的日变化,表现为单峰型,通常在地方时11:00~12:00左右达到碳吸收的最大值,平均为-0.2680mgCO2/(m2·s)(-6.0800μmolCO2/(m2·s))。白天的NEE与光合有效辐射之间符合很好的直角双曲线关系,表观量子产额平均为0.0203μmolCO2/μmolPAR,表观最大光合速率平均为9.7411μmolCO2/(m2·s)。夜晚的NEE与5cm地温有很好的指数函数关系。     

Responses of ecosystem carbon exchange to multi-level water addition in an alpine meadow in Namtso of Qinghai-Xizang Plateau,China

高寒草甸是青藏高原的主要草地类型, 对青藏高原生态系统碳收支具有重要的调节作用。目前, 有关高寒草甸生态系统碳交换对气候变化的响应所知甚少, 尤其是降水变化会如何影响高寒草甸碳交换过程的相关研究非常匮乏。该文作者于2013和2014年的生长季(5-9月)在青藏高原纳木错地区高寒草甸进行多梯度人工增水实验, 设置对照和5个水分添加梯度, 分别增加0%、20%、40%、60%、80%和100%的降水, 以研究高寒草甸生态系统在不同降水量条件下的碳交换变化。增水处理后, 各处理梯度之间的土壤温度没有显著差异, 而土壤含水量在不同增水处理后出现显著变化, 相对于对照, 增水幅度越大, 对应的土壤含水量越高。综合2013和2014年的观测结果, 高寒草甸生态系统整体表现为碳吸收, 在20%增水处理中, 净生态系统碳交换(NEE)达到最大值, 随着模拟的降水梯度进一步增加, NEE逐渐下降; 增水处理对生态系统呼吸(ER)无显著影响; 总生态系统生产力(GEP)的变化趋势与NEE一致, 即随着增水梯度增大, GEP先增加, 并在增水20%处理达到最大值, 随后GEP开始降低。研究表明, 在高寒草甸生态系统, 水分是影响GEP和NEE的重要因素, 对ER影响较弱; 未来适度的增水(20%-40%)能促进高寒草甸生态系统对碳的吸收。     

Year-round observations of the net ecosystem exchange of carbon dioxide in a native tallgrass prairie

An Ameriflux site was established in mid 1996 to study the exchange of CO₂ in a native tallgrass prairie of north‐central Oklahoma, USA. Approximately the first 20 months of measurements (using eddy covariance) are described here. This prairie, dominated by warm season C4 grasses, is typical of the central Kansas/northern Oklahoma region. During the first three weeks of the measurement period (mid‐July–early August 1996), moisture‐stress conditions prevailed. For the remainder of the period (until March 1998), however, soil moisture was nonlimiting. Mid‐day net ecosystem CO₂ exchange (NEE), under well‐watered conditions, reached a maximum magnitude of 1.4 mg CO₂ m^?2 s^?1 (flux toward the surface is positive) during peak growth (mid‐July 1997), with green leaf area index of 2.8. In contrast, under moisture‐stress conditions in the same growth stage in 1996, mid‐day NEE was reduced to near‐zero. Average night NEE ranged from near‐zero, during winter dormancy, to ? 0.50 mg CO₂ m^?2 s^?1, during peak growth. Most of the variance in average night NEE was explained by changes in soil temperature (0.1 m depth) and green leaf area. The daytime NEE measurements were examined in terms of a rectangular hyperbolic relationship with incident photosynthetically active radiation. The analysis showed that the quantum yield during peak growth was similar to those measured in other prairies and the y‐intercept, so obtained, can be potentially used as an estimate of night‐time CO₂ emissions when eddy covariance data are unavailable. Daily integrated NEE reached its peak magnitude of 30.8 g CO₂ m^?2 d^?1 (8.4 g C m^?2 d^?1) in mid‐July when the green LAI was the largest (about 2.8). In general, the seasonal trend of daily NEE (on relatively clear days) followed that of green LAI. Annually integrated carbon exchange, between prescribed burns in 1997 and 1998, was 268 g C m^?2 y^?1. After incorporating carbon loss during the prescribed burn , the net annual carbon exchange in this prairie was near‐zero in 1998.     

青藏高原纳木错高寒草甸生态系统碳交换对多梯度增水的响应

高寒草甸是青藏高原的主要草地类型, 对青藏高原生态系统碳收支具有重要的调节作用。目前, 有关高寒草甸生态系统碳交换对气候变化的响应所知甚少, 尤其是降水变化会如何影响高寒草甸碳交换过程的相关研究非常匮乏。该文作者于2013和2014年的生长季(5-9月)在青藏高原纳木错地区高寒草甸进行多梯度人工增水实验, 设置对照和5个水分添加梯度, 分别增加0%、20%、40%、60%、80%和100%的降水, 以研究高寒草甸生态系统在不同降水量条件下的碳交换变化。增水处理后, 各处理梯度之间的土壤温度没有显著差异, 而土壤含水量在不同增水处理后出现显著变化, 相对于对照, 增水幅度越大, 对应的土壤含水量越高。综合2013和2014年的观测结果, 高寒草甸生态系统整体表现为碳吸收, 在20%增水处理中, 净生态系统碳交换(NEE)达到最大值, 随着模拟的降水梯度进一步增加, NEE逐渐下降; 增水处理对生态系统呼吸(ER)无显著影响; 总生态系统生产力(GEP)的变化趋势与NEE一致, 即随着增水梯度增大, GEP先增加, 并在增水20%处理达到最大值, 随后GEP开始降低。研究表明, 在高寒草甸生态系统, 水分是影响GEP和NEE的重要因素, 对ER影响较弱; 未来适度的增水(20%-40%)能促进高寒草甸生态系统对碳的吸收。     

Temperature controls ecosystem CO2 exchange of an alpine meadow on the northeastern Tibetan Plateau

Alpine ecosystems are extremely vulnerable to climate change. To address the potential variability of the responses of alpine ecosystems to climate change, we examined daily CO₂ exchange in relation to major environmental variables. A dataset was obtained from an alpine meadow on the Qinghai‐Tibetan Plateau from eddy covariance measurements taken over 3 years (2002–2004). Path analysis showed that soil temperature at 5 cm depth (T_s5) had the greatest effect on daily variation in ecosystem CO₂ exchange all year around, whereas photosynthetic photon flux density (PPFD) had a high direct effect on daily variation in CO₂ flux during the growing season. The combined effects of temperature and light regimes on net ecosystem CO₂ exchange (NEE) could be clearly categorized into three areas depending on the change in T_s5: (1) almost no NEE change irrespective of variations in light and temperature when T_s5 was below 0 °C; (2) an NEE increase (i.e. CO₂ released from the ecosystem) with increasing T_s5, but little response to variation in light regime when 0 °C≤T_s5≤8 °C; and (3) an NEE decrease with increase in T_s5 and PPFD when T_s5 was approximately >8 °C. The highest daily net ecosystem CO₂ uptake was observed under the conditions of daily mean T_s5 of about 15 °C and daily mean PPFD of about 50 mol m⁻² day⁻¹. The results suggested that temperature is the most critical determinant of CO₂ exchange in this alpine meadow ecosystem and may play an important role in the ecosystem carbon budget under future global warming conditions.     

A growing season climatic index to simulate gross primary productivity and carbon budget in a Tibetan alpine meadow

Accurate estimation of gross primary production (GPP) of ecosystem is needed to evaluate terrestrial carbon cycle at various spatial and temporal scales. Eddy covariance (EC) technique provides continuous measurements of net ecosystem CO₂ exchange (NEE) and can be used to separate GPP from NEE in real time series. However, seasonal and inter-annual variation and consequently ecosystem carbon budget is still very difficult to simulate from climatic and environment. To address this limitation, we develop a growing season indicator (GSI) based on low temperature and soil water stress to model and predict intra and inter-annual dynamic of gross primary productivity (GPP). Validation of this new index was conducted using continuous six-year consective EC measurement from 2004 to 2009 at a Tibetan alpine meadow. Simulated GPP agreed well with the observed GPP in terms of seasonal and inter-annual variation. The six-year correlation coefficients on seasonal scale between GSI and scalar GPP derived from EC reached more than 0.85 no matter in dry years or wet years. In addition, the temporal GPP estimation derived from GSI model was quite similar to those from observed values by EC measurement. Moreover, accumulated GSI values can predict annual variability of net ecosystem production (NEP). Higher yearly accumulated GSI corresponded to more annual NEP. When cumulative GSI arrived up to 92, the target ecosystem was a carbon sink. This is probably a threshold which Tibetan alpine meadow changes from carbon source to carbon sink. It is indicated that the GSI model is a simple, alternative approach to estimating GPP and has the potential to simulate spatial GPP in a larger scale. However, the performance of GSI model in other vegetation types or regions still needs a further verification.     

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.     

The use of eddy covariance to infer the net carbon dioxide uptake of Brazilian rain forest

• 1 Eddy covariance measurements of CO₂ flux, based on four and six week campaigns in Rondôdnia, Brazil, have been used in conjunction with a model to scale up data to a whole year, and thus estimate the carbon balance of the tropical forest ecosystem, and the changes in carbon balance expected from small interannual variations in climatological conditions.
• 2 One possible source of error in this estimation arises from the difficulty in measuring fluxes under stably stratified meteorological conditions, such as occur frequently at night. Flux may be ‘lost’ because of low velocity advection, caused by nocturnal radiative cooling at sites on raised ground. Such effects may be detected by plotting the net ecosystem flux of CO₂, F_eco is a function of wind speed. If flux is ‘lost’ then F_eco is expected to decline with wind speed. In the present data set, this did not occur, and F_eco was similar to the nocturnal flux estimated independently from chamber measurements.
• 3 The model suggests that in 1992/3, the Gross Primary Productivity (GPP) was 203.3 mol C m^?2 y^?1 and ecosystem respiration was 194.8 mol C m^?2 y^?1, giving an ecosystem carbon balance of 8.5 mol C m^?2 y^?1, equivalent to a sink of 1.0 ton C ha^?1 y^?1. However, the sign and magnitude of this figure is very sensitive to temperature, because of the strong influence of temperature on respiration.
• 4 The model also suggests that the effect of temperature on the net carbon balance is strongly dependent on the partial pressure of CO₂.

     

Phylogeographical Study on Eriophyton wallichii (Labiatae) from Alpine Scree of Qinghai Tibetan Plateau

In this study, we examined the nuclear ribosomal DNA internal transcribed spacer (ITS) sequence variation of Eriophyton wallichii, a perennial endemic to alpine scree of the Qinghai Tibetan Plateau. Nineteen haplotypes were detected by analyzing 187 individuals from 20 populations of E.wallichii. Most populations hold the unique haplotype, which showed different population with different haplotype. An analysis of molecular variance (AMOVA) for populations showed that the genetic variation mainly resided among populations (89.54%), the level of differentiation among populations was very high (GST=0.863; NST=0.957) but didn’t show a significant phylogeographical structure. It is different from foregoing other species reported in Qinghai Tibetan Plateau that the haplotypes of E.wallichii showed a distribution pattern that almost one population hold one unique haplotype, hardly share same halotype among populations.We hypothesized the unique genetic structure of E.wallichii might result from allopatric fragmentation in the “islands of alpine” due to the extremely isolated alpine scree and rough topography of the region, through the Quaternary climate oscillation dramatically caused population expanding or shrinking.     

Estimating air temperature of an alpine meadow on the Northern Tibetan Plateau using MODIS land surface temperature

Meteorological data are scarce due to lack of meteorology stations in the Qinghai–Tibet Plateau. This often results in an imprecise estimation of air temperature. A linear estimation of air temperature of an alpine meadow on Northern Tibetan Plateau at heights of 1.5 m–2.1 m by using MODIS land surface temperature (LST) data was conducted in this study. The results showed that linear estimation of daily maximum and daytime mean air temperatures from MODIS LST data were not accurate enough (P > 0.01, R² < 0.10) during the growing season. In contrast, the linear relationships between daily maximum and daytime mean air temperature and MODIS LST during the non-growing season were both significant (P < 0.01, R² > 0.40). MODIS LST data were accurate enough to linearly estimate daily minimum and nighttime mean air temperatures (P < 0.01, R² > 0.55). Moreover, derived LST from MODIS/Terra platform (MOD11A2) had higher accuracies than derived LST from MODIS/Aqua platform (MYD11A2) in linearly estimating air temperatures mentioned above.     

三江并流核心区亚高山森林非生长季净生态系统CO2交换量及其影响因素

采用开路式涡度相关系统,针对三江并流核心区西藏红拉山滇金丝猴国家自然保护区,通过测量和分析非生长季亚高山常绿针叶林净生态系统碳交换量(NEE),探讨了亚高山森林非生长季CO₂通量特征及其主要影响因子。保护区常绿针叶林NEE值在非生长季具有明显“U”型变化曲线,白天表现为碳吸收,夜间表现为碳释放,日间CO₂吸收高峰介于12:00到15:00之间,平均每天碳汇时间在10 h左右。非生长季各月NEE大小依次为：4月> 3月>2月>11月>1月>12月。研究期内气温(T)、相对湿度(RH)、饱和水汽压差(VPD)和光合有效辐射(PAR)等气象因子对净生态系统CO₂交换量影响显著。此外,森林碳吸收对温度响应敏感,光合作用在整个非生长季较为明显。各影响因子中光合有效辐射对碳交换影响最大;夜间NEE与5 cm土壤温度呈极显著相关性(P<0.01)且NEE随着土壤温度升高而增大;整个非生长季NEE、生态系统呼吸量(Re)和总生态系统CO₂交换量(GEE)分别为-596.759 g...     

Estimating air temperature of an alpine meadow on the Northern Tibetan Plateau using MODIS land surface temperature

Meteorological data are scarce due to lack of meteorology stations in the Qinghai–Tibet Plateau. This often results in an imprecise estimation of air temperature. A linear estimation of air temperature of an alpine meadow on Northern Tibetan Plateau at heights of 1.5 m–2.1 m by using MODIS land surface temperature (LST) data was conducted in this study. The results showed that linear estimation of daily maximum and daytime mean air temperatures from MODIS LST data were not accurate enough (P > 0.01, R² < 0.10) during the growing season. In contrast, the linear relationships between daily maximum and daytime mean air temperature and MODIS LST during the non-growing season were both significant (P < 0.01, R² > 0.40). MODIS LST data were accurate enough to linearly estimate daily minimum and nighttime mean air temperatures (P < 0.01, R² > 0.55). Moreover, derived LST from MODIS/Terra platform (MOD11A2) had higher accuracies than derived LST from MODIS/Aqua platform (MYD11A2) in linearly estimating air temperatures mentioned above.     

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。     

青藏高原高寒草甸生态系统碳增汇潜力

为了揭示青藏高原高寒草甸生态系统植被变化对碳储量的影响,以原生矮嵩草草甸、退化草甸、人工草地以及农田为研究对象,对比分析了该4种不同土地格局下生态系统的有机碳现状.以原生矮嵩草草甸土壤碳储量为基准对不同类型高寒生态系统的碳增汇潜力进行了估算.结果表明:不同类型生态系统的碳储量和碳增汇潜力有很大差异,在0-40cm土层中,(1)原生草甸碳储量最高,达到17098 g C/m2,退化草甸、人工草地和农田的有机碳汇增加潜力分别为:5637、3823、1567 g C/m2.(2)对于退化草甸和人工草地,土壤有机碳含量和密度明显低于原生草甸和农田.(3)地下生物量碳储量主要集中在0-20cm,且原生草甸地下生物量的碳储量比其他3个植被类型高3.6-5倍.总体上,青藏高原草地生态系统存在巨大的碳增汇潜力.     

青藏高原东缘高寒草原有毒植物分布与高原鼠兔、高原鼢鼠的相关性

青藏高原高寒草原生态系统是我国特有的生态系统类型,由于受到人为破坏的影响,目前该地区草原生态系统功能退化,优良牧草减少,有毒植物蔓延。高原鼠兔(Ochotona curzoniae)和高原鼢鼠(Myospalax baileyi)是青藏高原东缘高寒草原中最重要的两种小型哺乳动物,其采食行为和挖掘洞穴的生活特性必然对生态系统产生影响,但其与有毒植物之间的互作关系尚未揭示。基于此,在甘肃省玛曲县河曲马场自然生长的高寒草原生态系统中开展了有毒植物的分布与高原鼠兔、高原鼢鼠之间的相关性研究。结果表明,该高寒草原生态系统中分布有毒植物27种,分属于菊科、豆科、毛茛科等11科。在此基础上,测定了该地区有毒植物的生物多样性指数、均匀度指数和丰富度指数,并探究了单位面积条件下有毒植物的分布特征与高原鼠兔和高原鼢鼠种群密度之间的相关性,发现该地区高寒草原有毒植物的蔓延与高原鼠兔的密度之间存在密切的负相关关系(P0.05),而与高原鼢鼠的相关性不显著(P0.05)。     

青藏高原高寒湿地生态系统CO2通量

依据涡度相关系统连续观测的2005年CO2通量数据,对青藏高原东北隅的高寒湿地生态系统源/汇功能及其部分环境影响因素进行了分析.结果表明,高寒湿地生态系统为明显的碳源,在植物生长季(5～9月份)吸收230.16 gCO2·m-2,非生长季(1～4月份及10～12月份)释放546.18 gCO2·m-2,其中净排放最高在5月份,为181.49 gCO2·m-2,净吸收最高在8月份,为189.69 gCO2·m-2,年释放量为316.02 gCO2·m-2.在平均日变化中,最大吸收值出现在7月份12:00,为(0.45±0.0012) mgCO2·m-2·s-1,最大排放速率出现在8月份0:00,为(0.22±0.0090) mgCO2·m-2·s-1.生长季中6～9月份表现为明显的单峰型日变化,非生长季的变化幅度较小.净生态系统交换量(NEE)和生态系统总初级生产力(GPP)与气温、空气水气饱和亏和地表反射率等环境因素呈现相似的相关性,与地上生物量和群落叶面积指数则为线性负相关,生态系统呼吸(Res)则与上述因子的相关性呈现相反的趋势.     

辐射变化对中亚热带杉木人工林净CO2交换的影响

太阳总辐射是影响森林生态系统碳交换的重要因子.为认识辐射变化对杉木人工林碳交换的影响,本研究利用开路式涡度相关系统和气象梯度观测系统测得的CO2通量和气象因子长期定位监测数据,用晴空指数(kt)表示太阳辐射情况,分析了kt对中亚热带杉木人工林生长季(4-10月)净C02交换(NEE)的影响.结果 表明:晴天时的太阳总辐...     

陆地生态系统碳水通量贡献区评价综述

综述了通量贡献区研究的基本理论、最新进展、研究热点与难点,旨在促进中国区域碳水通量数据空间代表性的定量评价.通量贡献区是通量观测点上风向的空间代表区域,能够反映代表区域对应下垫面的源区内每一点对观测点的通量贡献权重影响,主要受观测高度、空气动力学粗糙度和大气稳定度等因素的影响.通量贡献区通常随着观测高度的增加、空气动力学粗糙度的降低和大气稳定度的增加而变大,反之则变小.通量贡献区的评价模型包括解析模型、拉格朗日随机模型、大涡模拟和闭合模型四类.通量贡献区的评价结果可以广泛应用于通量数据质量评价、实验设计的指导、与遥感技术结合的区域尺度的总初级生产力的估算、城市CO2通量变化的评估以及能量闭合的评价等研究.最新研究表明,对流边界层的通量贡献区存在负的通量贡献区域;有裸地存在的情况下解析模型通常会低估裸地对观测通量的贡献;与水平地面处的通量贡献区相比,山谷处通量贡献区变小而山脊处的通量贡献区变大.通量贡献区模型研究应进一步考虑大气中的平流效应、湍流的非高斯扩散以及建立冠层内部的通量贡献区模型.解决森林冠层内流场的不均匀性、冠层重叠问题、冠层湍流的不稳定性是建立适合冠层内部通量贡献区模型的前提条件.在理想条件的气体释放验证试验的基础上,需要开展复杂条件下的相关试验.     

Seasonal net carbon dioxide exchange of a beech forest with the atmosphere

The seasonal carbon dioxide exchange of a beech forest of Central Italy was studied by means of the eddy covariance technique. Additional measurements of biomass respiration with cuvettes and relationship of carbon dioxide exchanges with temperature and light were used to interpolate missing data during the dormant and part of the growing season. The net ecosystem production of the forest equals 472 g C m^?2 y^?1 while the gross ecosystem production 1016 g C m^?2 y^?1 and respiration 544 g C m^?2 y^?1. These estimates are compared with the net primary production determined by direct biomass sampling which amounts to 802 g C m^?2 y^?1.