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1.
The study by the eddy covariance technique in the alpine shrub meadow of the Qinghai-Tibet Plateau in 2003 and 2004 showed that the net ecosystem carbon dioxide exchange (NEE) exhibited noticeable diurnal and annual variations, with more distinct daily changes during the warmer seasons. The CO 2 emission of the shrub ecosystem culminated in April and September while the CO 2 absorption capacity reached a maximum in July and August. The absorbed carbon dioxide during the two consecutive years was 231.4 and 274.8 g CO 2·m ?2 respectively, yielding an average of 253.1 gCO 2·m ?2 per year: that accounts for a large proportion of absorbed CO 2 in the region. Obviously, the diurnal carbon flux was negatively related to temperature, radiation and other atmospheric factors. Still, minute discrepancies in kurtosis and duration of carbon emission/absorption were detected between 2003 and 2004. It was found that the CO 2 flux in the daytime was similarly affected by photosynthetic photon flux density in both years. Temperature appears to be the most important determinant of CO 2 flux: specifically, the high temperature during the plant growing season inhibits the carbon absorption capacity. One potential explanation is that soil respiration is enhanced under such condition. Analysis of biomass revealed that the annual net carbon fixed capacity of aboveground and belowground biomass was 544.0 in 2003 and 559.4 g C·m ?2 in 2004, which coincided with the NEE absorption capacity (63.1 g C·m ?2 in 2003 and 74.9 g C·m ?2 in 2004) in the corresponding plant growing season. 相似文献
2.
As one component of ChinaFLUX, the measurement of CO2 flux using eddy covariance over subtropical planted coniferous ecosystem in Qianyanzhou was conducted for a long term. This paper discusses the seasonal dynamics of net ecosystem exchange (NEE), ecosystem respiration (RE) and gross ecosystem exchange (GEE) between the coniferous ecosystem and atmosphere along 2003 and 2004. The variations of NEE, RE and GEE show obvious seasonal variabilities and correlate to each other, i.e. lower in winter and drought season, but higher in summer; light, temperature and soil water content are the main factors determining NEE; air temperature and water vapor pressure deficit (VPD) influence NEE with stronger influence from VPD. Under the proper light condition, drought stress could decrease the temperature range for carbon capture in planted coniferous, air temperature and precipitation controlled RE; The NEE, RE, and GEE for planted coniferous in Qianyanzhou are −387.2 g C·m−2 a−1, 1223.3 g C·m−2 a−1, −1610.4 g C·m−2 a−1 in 2003 and −423.8 g C·m−2 a−1, 1442.0 g C·m−2 a−1, −1865.8 g C·m−2 a−1 in 2004, respectively, which suggest the intensive ability of plantation coniferous forest on carbon absorbing in Qianyanzhou. 相似文献
3.
As one component of ChinaFLUX, the measurement of CO 2 flux using eddy covariance over subtropical planted coniferous ecosystem in Qianyanzhou was conducted for a long term. This paper discusses the seasonal dynamics of net ecosystem exchange (NEE), ecosystem respiration (RE) and gross ecosystem exchange (GEE) between the coniferous ecosystem and atmosphere along 2003 and 2004. The variations of NEE, RE and GEE show obvious seasonal variabilities and correlate to each other, i.e. lower in winter and drought season, but higher in summer; light, temperature and soil water content are the main factors determining NEE; air temperature and water vapor pressure deficit (VPD) influence NEE with stronger influence from VPD. Under the proper light condition, drought stress could decrease the temperature range for carbon capture in planted coniferous, air temperature and precipitation controlled RE; The NEE, RE, and GEE for planted coniferous in Qianyanzhou are ?387.2 g C·m ?2 a ?1, 1223.3 g C·m ?2 a ?1, ?1610.4 g C·m ?2 a ?1 in 2003 and ?423.8 g C·m ?2 a ?1, 1442.0 g C·m ?2 a ?1, ?1865.8 g C·m ?2 a ?1 in 2004, respectively, which suggest the intensive ability of plantation coniferous forest on carbon absorbing in Qianyanzhou. 相似文献
4.
Eddy covariance technique was used to measure carbon flux during two growing seasons in 2003 and 2004 over typical steppe in the Inner Mongolia Plateau, China. The results showed that there were two different CO2 flux diurnal patterns at the grassland ecosystem. One had a dual peak in diurnal course of CO2 fluxes with a depression of CO2 flux after noon, and the other had a single peak. In 2003, the maximum diurnal uptake and emitting value of CO2 were −7.4 and 5.4 g·m−2·d−1 respectively and both occurred in July. While in 2004, the maximum diurnal uptake and release of CO2 were −12.8 and 5.8 g·m−2·d−1 and occurred both in August. The grassland fixed 294.66 and 467.46 g CO2·m−2 in 2003 and 2004, and released 333.14 and 437.17 g CO2·m−2 in 2003 and 2004, respectively from May to September. Water availability and photosynthetic active radiation (PAR) are two important factors of controlling CO2 flux. Consecutive precipitation can cause reduction in the ability of ecosystem carbon exchange. Under favorable soil water conditions, daytime CO2 flux is dependent on PAR. CO2 flux, under soil water stress conditions, is obviously less than those under favorable soil water conditions, and there is a light saturation phenomena at PAR=1200 μmol·m−2·s−1. Soil respiration was temperature dependent when there was no soil water stress; otherwise, this response became accumulatively decoupled from soil temperature. 相似文献
5.
Eddy covariance technique was used to measure carbon flux during two growing seasons in 2003 and 2004 over typical steppe in the Inner Mongolia Plateau, China. The results showed that there were two different CO 2 flux diurnal patterns at the grassland ecosystem. One had a dual peak in diurnal course of CO 2 fluxes with a depression of CO 2 flux after noon, and the other had a single peak. In 2003, the maximum diurnal uptake and emitting value of CO 2 were ?7.4 and 5.4 g·m ?2·d ?1 respectively and both occurred in July. While in 2004, the maximum diurnal uptake and release of CO 2 were ?12.8 and 5.8 g·m ?2·d ?1 and occurred both in August. The grassland fixed 294.66 and 467.46 g CO 2·m ?2 in 2003 and 2004, and released 333.14 and 437.17 g CO 2·m ?2 in 2003 and 2004, respectively from May to September. Water availability and photosynthetic active radiation ( PAR) are two important factors of controlling CO 2 flux. Consecutive precipitation can cause reduction in the ability of ecosystem carbon exchange. Under favorable soil water conditions, daytime CO 2 flux is dependent on PAR. CO 2 flux, under soil water stress conditions, is obviously less than those under favorable soil water conditions, and there is a light saturation phenomena at PAR=1200 μmol·m ?2·s ?1. Soil respiration was temperature dependent when there was no soil water stress; otherwise, this response became accumulatively decoupled from soil temperature. 相似文献
6.
Long-term measurement of carbon metabolism of old-growth forests is critical to predict their behaviors and to reduce the uncertainties of carbon accounting under changing climate. Eddy covariance technology was applied to investigate the long-term carbon exchange over a 200 year-old Chinese broad-leaved Korean pine mixed forest in the Changbai Mountains (128°28′E and 42°24′N, Jilin Province, P. R. China) since August 2002. On the data obtained with open-path eddy covariance system and CO2 profile measurement system from Jan. 2003 to Dec. 2004, this paper reports (i) annual and seasonal variation of F
NEE, F
GPP and R
E; (ii) regulation of environmental factors on phase and amplitude of ecosystem CO2 uptake and release Corrections due to storage and friction velocity were applied to the eddy carbon flux. LAI and soil temperature determined the seasonal and annual dynamics of FGPP and RE separately. VPD and air temperature regulated ecosystem photosynthesis at finer scales in growing seasons. Water condition at the root zone exerted a significant influence on ecosystem maintenance carbon metabolism of this forest in winter. The forest was a net sink of atmospheric CO2 and sequestered −449 g C·m−2 during the study period; −278 and −171 gC·m−2 for 2003 and 2004 respectively. F
GPP and F
RE over 2003 and 2004 were −1332, −1294 g C·m−2. and 1054, 1124 g C·m−2 respectively. This study shows that old-growth forest can be a strong net carbon sink of atmospheric CO2. There was significant seasonal and annual variation in carbon metabolism. In winter, there was weak photosynthesis while the ecosystem emitted CO2. Carbon exchanges were active in spring and fall but contributed little to carbon sequestration on an annual scale. The summer is the most significant season as far as ecosystem carbon balance is concerned. The 90 days of summer contributed 66.9, 68.9% of F
GPP, and 60.4, 62.1% of R
E of the entire year. 相似文献
7.
CO 2 flux was measured continuously in a wheat and maize rotation system of North China Plain using the eddy covariance technique to study the characteristic of CO 2 exchange and its response to key environmental factors. The results show that nighttime net ecosystem exchange (NEE) varied exponentially with soil temperature. The temperature sensitivities of the ecosystem ( Q 10) were 2.94 and 2.49 in years 2002–2003 and 2003–2004, respectively. The response of gross primary productivity (GPP) to photosynthetically active radiation (PAR) in the crop field can be ex-pressed by a rectangular hyperbolic function. Average A max and α for maize were more than those for wheat. The values of α increased positively with leaf area index (LAI) of wheat. Diurnal variations of NEE were significant from March to May and from July to September, but not remarkable in other months. NEE, GPP and ecosystem respiration ( R ec) showed significantly seasonal variations in the crop field. The highest mean daily CO 2 uptake rate was ?10.20 and ?12.50 gC·m ?2?d ?1 in 2003 and 2004, for the maize field, respectively, and ?8.19 and ?9.50 gC?m ?2·d ?1 in 2003 and 2004 for the wheat field, respectively. The maximal CO 2 uptake appeared in April or May for wheat and mid-August for maize. During the main growing seasons of winter wheat and summer maize, NEE was controlled by GPP which was chiefly influenced by PAR and LAI. R ec reached its annual maximum in July when R ec and GPP contributed to NEE equally. NEE was dominated by R ec in other months and temperature became a key factor controlling NEE. Total NEE for the wheat field was ?77.6 and ?152.2 gC·m ?2·a ?1 in years 2002–2003 and 2003–2004, respectively, and ?120.1 and ?165.6 gC·m ?2·a ?1 in 2003 and 2004 for the maize field, respectively. The cropland of North China Plain was a carbon sink, with annual ?197.6 and ?317.9 gC·m ?2·a ?1 in years 2002–2003 and 2003–2004, respectively. After considering the carbon in grains, the cropland became a carbon source, which was 340.5 and 107.5 gC·m ?2·a ?1 in years 2002–2003 and 2003–2004, respectively. Affected by climate and filed managements, inter-annual carbon exchange varied largely in the wheat and maize rotation system of North China Plain. 相似文献
8.
Long-term measurement of carbon metabolism of old-growth forests is critical to predict their behaviors and to reduce the uncertainties of carbon accounting under changing climate. Eddy covariance technology was applied to investigate the long-term carbon exchange over a 200 year-old Chinese broad-leaved Korean pine mixed forest in the Changbai Mountains (128°28′E and 42°24′N, Jilin Province, P. R. China) since August 2002. On the data obtained with open-path eddy covariance system and CO 2 profile measurement system from Jan. 2003 to Dec. 2004, this paper reports (i) annual and seasonal variation of F NEE, F GPP and R E; (ii) regulation of environmental factors on phase and amplitude of ecosystem CO 2 uptake and release Corrections due to storage and friction velocity were applied to the eddy carbon flux. LAI and soil temperature determined the seasonal and annual dynamics of FGPP and RE separately. VPD and air temperature regulated ecosystem photosynthesis at finer scales in growing seasons. Water condition at the root zone exerted a significant influence on ecosystem maintenance carbon metabolism of this forest in winter.The forest was a net sink of atmospheric CO 2 and sequestered ?449 g C·m ?2 during the study period; ?278 and ?171 gC·m ?2 for 2003 and 2004 respectively. F GPP and F RE over 2003 and 2004 were ?1332, ?1294 g C·m ?2. and 1054, 1124 g C·m ?2 respectively. This study shows that old-growth forest can be a strong net carbon sink of atmospheric CO 2.There was significant seasonal and annual variation in carbon metabolism. In winter, there was weak photosynthesis while the ecosystem emitted CO 2. Carbon exchanges were active in spring and fall but contributed little to carbon sequestration on an annual scale. The summer is the most significant season as far as ecosystem carbon balance is concerned. The 90 days of summer contributed 66.9, 68.9% of F GPP, and 60.4, 62.1% of R E of the entire year. 相似文献
9.
We present an uncertainty analysis of ecological process parameters and CO 2 flux components ( R
eco, NEE and gross ecosystem exchange ( GEE)) derived from 3 years’ continuous eddy covariance measurements of CO 2 fluxes at subtropical evergreen coniferous plantation, Qianyanzhou of ChinaFlux. Daily-differencing approach was used to
analyze the random error of CO 2 fluxes measurements and bootstrapping method was used to quantify the uncertainties of three CO 2 flux components. In addition, we evaluated different models and optimization methods in influencing estimation of key parameters
and CO 2 flux components. The results show that: (1) Random flux error more closely follows a double-exponential (Laplace), rather
than a normal (Gaussian) distribution. (2) Different optimization methods result in different estimates of model parameters.
Uncertainties of parameters estimated by the maximum likelihood estimation (MLE) are lower than those derived from ordinary
least square method (OLS). (3) The differences between simulated R eco, NEE and GEE derived from MLE and those derived from OLS are 12.18% (176 g C·m −2·a −1), 34.33% (79 g C·m −2·a −1) and 5.4% (92 g C·m −2·a −1). However, for a given parameter optimization method, a temperature-dependent model (T_model) and the models derived from
a temperature and water-dependent model (TW_model) are 1.31% (17.8 g C·m −2·a −1), 2.1% (5.7 g C·m −2·a −1), and 0.26% (4.3 g C·m −2·a −1), respectively, which suggested that the optimization methods are more important than the ecological models in influencing
uncertainty in estimated carbon fluxes. (4) The relative uncertainty of CO 2 flux derived from OLS is higher than that from MLE, and the uncertainty is related to timescale, that is, the larger the
timescale, the smaller the uncertainty. The relative uncertainties of R eco, NEE and GEE are 4%−8%, 7%−22% and 2%−4% respectively at annual timescale.
Supported by the National Natural Science Foundation of China (Grant No. 30570347), Innovative Research International Partnership
Project of the Chinese Academy of Sciences (Grant No. CXTD-Z2005-1) and National Basic Research Program of China (Grant No.
2002CB412502) 相似文献
10.
The Dinghushan flux observation site, as one of the four forest sites of ChinaFLUX, aims to acquire long-term measurements of CO2 flux over a typical southern subtropical evergreen coniferous and broad-leaved mixed forest ecosystem using the open path eddy covariance method. Based on two years of data from 2003 to 2004, the characteristics of temporal variation in CO2 flux and its response to environmental factors in the forest ecosystem are analyzed. Provided two-dimensional coordinate rotation, WPL correction and quality control, poor energy-balance and underestimation of ecosystem respiration during nighttime implied that there could be a CO2 leak during the nighttime at the site. Using daytime (PAR > 1.0 μmol−1·m−2·s−1) flux data during windy conditions (u* > 0.2 m·s−1), monthly ecosystem respiration (Reco) was derived through the Michaelis-Menten equation modeling the relationship between net ecosystem C02 exchange (NEE) and photosynthetically active radiation (PAR). Exponential function was employed to describe the relationship between Reco and soil temperature at 5 cm depth (Ts05), then Reco of both daytime and nighttime was calculated respectively by the function. The major results are: (i) Derived from the Michaelis-Menten equation, the apparent quantum yield (α) was 0.0027±0.0011 mgCO2·μmol−1 photons, and the maximum photosynthetic assimilation rate (Amax) was 1.102±0.288 mgCO2·m−2·s−1. Indistinctive seasonal variation of α or Amax was consistent with weak seasonal dynamics of leaf area index (LAf) in such a lower subtropical evergreen mixed forest, (ii) Monthly accumulated Reco was estimated as 95.3±21.1 gC·m−2mon−1, accounting for about 68% of the gross primary product (GPP). Monthly accumulated WEE was estimated as −43.2±29.6 gC·m−2·mon−1. The forest ecosystem acted as carbon sink all year round without any seasonal carbon efflux period. Annual NEE of 2003 and 2004 was estimated as −563.0 and −441.2 gC·m−2·a−1 respectively, accounting for about 32% of GPP. 相似文献
11.
We measured soil, stem and branch respiration of trees and shrubs, foliage photosynthesis and respiration in ecosystem of the needle and broad-leaved Korean pine forest in Changbai Mountain by LI-6400 CO 2 analysis system. Measurement of forest microclimate was conducted simultaneously and a model was found for the relationship of soil, stem, leaf and climate factors. CO 2 flux of different components in ecosystem of the broad-leaved Korean pine forest was estimated based on vegetation characteristics. The net ecosystem exchange was measured by eddy covariance technique. And we studied the effect of temperature and photosynthetic active radiation on ecosystem CO 2 flux. Through analysis we found that the net ecosystem exchange was affected mainly by soil respiration and leaf photosynthesis. Annual net ecosystem exchange ranged from a minimum of about ?4.671 μmol·m ?2·s ?1 to a maximum of 13.80 μmol·m ?2·s ?1, mean net ecosystem exchange of CO 2 flux was ?2.0 μmol·m ?2·s ?1 and 3.9 μmol·m ?2·s ?1 in winter and summer respectively (mean value during 24 h). Primary productivity of tree, shrub and herbage contributed about 89.7%, 3.5% and 6.8% to the gross primary productivity of the broad-leaved Korean pine forest respectively. Soil respiration contributed about 69.7% CO 2 to the broad-leaved Korean pine forest ecosystem, comprising about 15.2% from tree leaves and 15.1% from branches. The net ecosystem exchange in growing season and non-growing season contributed 56.8% and 43.2% to the annual CO 2 efflux respectively. The ratio of autotrophic respiration to gross primary productivity ( R a:GPP) was 0.52 (NPP:GPP=0.48). Annual carbon accumulation underground accounted for 52% of the gross primary productivity, and soil respiration contributed 60% to gross primary productivity. The NPP of the needle and broad-leaved Korean pine forest was 769.3 gC·m ?2·a ?1. The net ecosystem exchange of this forest ecosystem (NEE) was 229.51 gC·m ?2·a ?1. The NEE of this forest ecosystem acquired by eddy covariance technique was lower than chamber estimates by 19.8%. 相似文献
12.
The dissolved CO 2 concentration of stream waters is an important component of the terrestrial carbon cycle. This study reconstructs long‐term records of dissolved CO 2 concentration for the outlets of two large catchments (818 and 586 km 2) in northern England. The study shows that: - 1. The flux of dissolved CO2 from the catchments (as carbon per catchment area), when adjusted for that which would be carried by the river water at equilibrium with the atmosphere, is between 0 and 0·39 t km−2 year−1 for the River Tees and between 0 and 0·65 t km−2 year−1 for the River Coquet.
- 2. The flux of dissolved CO2 is closely correlated with dissolved organic carbon (DOC) export and is unrelated to dissolved CO2 export from the headwaters of the study catchments.
- 3. The evasion rate of CO2 from the rivers (as carbon per stream area) is between 0·0 and 1·49 kg m−2 year−1, and calculated in‐stream productions of CO2 are estimated as between 0·5 and 2·5% of the stream evasion rate.
- 4. By mass balance, it is estimated that 8% of the annual flux of DOC is lost within the streams of the catchment.
The study shows that the loss of CO 2 from the streams of the Tees catchment is between 3·1 and 7·5 kt year −1 (as carbon) for the River Tees, which is the same order as annual CH 4 flux from peats within the catchment and approximately 50% of the net CO 2 exchange to the peats of the catchment. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
13.
As the substantial component of the ecosystem respiration, soil CO 2 flux is strongly influenced by infrequent and unpredictable precipitation in arid region. In the current study, we investigated the response of soil CO 2 flux to rain pulses at a saline desert in western China. Soil CO 2 flux was measured continuously during the whole growing season of 2009 at six sites. We found that there were remarkable changes in amplitude or diurnal patterns of soil CO 2 flux induced by rainfall events: from bimodal before rain to a single peak after that. Further analysis indicated that there is a significant linear relationship ( P < 0.001) between soil CO 2 flux and soil temperature ( Tsoil). However, a hysteresis between the waveform of diurnal course of CO 2 flux and Tsoil was observed: with soil CO 2 flux always peaked earlier than Tsoil. Furthermore, a double exponential decay function was fitted to the soil CO 2 flux after rainfall, and total carbon (C) releases were estimated by numerical integration for rainfall events. The relative enhancement and total C release, in association with the rain pulses, was linearly related to the amount of precipitation. According to the size and frequency of rainfall events, the total amount of C release induced by rain pulses was computed as much as 7.88 g C·m –2 in 2009, equivalent to 10.25% of gross primary production. These results indicated that rain pulses played a significant role in the carbon budget of this saline desert ecosystem, and the size of them was a good indicator of rain‐induced flux enhancement. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
14.
Many studies on global climate have forecast major changes in the amounts and spatial patterns of precipitation that may significantly affect temperate grasslands in arid and semi-arid regions. As a part of ChinaFLUX, eddy covariance flux measurements were made at a semi-arid Leymus chinensis steppe in Inner Mongolia, China during 2003–2004 to quantify the response of carbon exchange to environmental changes. Results showed that gross ecosystem production (F
GEP) and ecosystem respiration (R
eco) of the steppe were significantly depressed by water stress due to lack of precipitation during the growing season. Temperature was the dominant factor affecting F
GEP and R
eco in 2003, whereas soil moisture imposed a significant influence on both R
eco and F
GEP in 2004. Under wet conditions, R
eco showed an exponentially increasing trend with temperature (Q
10 = 2.0), but an apparent reduction in the value of R
eco and its temperature sensitivity were observed during the periods of water stress (Q
10=1.6). Both heat and water stress can cause decrease in F
GEP. The seasonality of ecosystem carbon exchange was strongly correlated with the variation of precipitation. With less precipitation in 2003, the steppe sequestrated carbon in June and July, and went into a senescence in early August due to water stress. As compared to 2003, the severe drought during the spring of 2004 delayed the growth of the steppe until late June, and the steppe became a CO2 sink from early July until mid-September, with ample precipitation in August. The semi-arid steppe released a total of 9.7 g C·m−2 from May 16 to the end of September 2003, whereas the net carbon budget during the same period in 2004 was close to zero. Long-term measurements over various grasslands are needed to quantify carbon balance in temperate grasslands. 相似文献
15.
This study uses long‐term records of stream chemistry, discharge and air temperature from two neighbouring forested catchments in the southern Appalachians in order to calculate production of dissolved CO 2 and dissolved inorganic carbon (DIC). One of the pair of catchments was clear‐felled during the period of the study. The study shows that: (1) areal production rates of both dissolved CO 2 and DIC are similar between the two catchments even during and immediately after the period of clear‐felling; (2) flux of total inorganic carbon (dissolved CO 2+ DIC) rises dramatically in response to a catchment‐wide acidification event; (3) DIC and dissolved CO 2 are dominantly released on the old water portion of the discharge and concentrations peak in the early autumn when flows in the study catchments are at their lowest; (4) total fluvial carbon flux from the clear‐felled catchment is 11·6 t km −2 year −1 and for the control catchment is 11·4 t km −2 year −1. The total inorganic carbon flux represents 69% of the total fluvial carbon flux. The method presented in the study provides a useful way of estimating inorganic carbon flux from a catchment without detailed gas monitoring. The time series of dissolved CO 2 at emergence to the stream can also be a proxy for the soil flux of CO 2. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
16.
The Dinghushan flux observation site, as one of the four forest sites of ChinaFLUX, aims to acquire long-term measurements of CO 2 flux over a typical southern subtropical evergreen coniferous and broad-leaved mixed forest ecosystem using the open path eddy covariance method. Based on two years of data from 2003 to 2004, the characteristics of temporal variation in CO 2 flux and its response to environmental factors in the forest ecosystem are analyzed. Provided two-dimensional coordinate rotation, WPL correction and quality control, poor energy-balance and underestimation of ecosystem respiration during nighttime implied that there could be a CO 2 leak during the nighttime at the site. Using daytime ( PAR > 1.0 μmol ?1·m ?2·s ?1) flux data during windy conditions ( u* > 0.2 m·s ?1), monthly ecosystem respiration ( Reco) was derived through the Michaelis-Menten equation modeling the relationship between net ecosystem C0 2 exchange ( NEE) and photosynthetically active radiation ( PAR). Exponential function was employed to describe the relationship between Reco and soil temperature at 5 cm depth ( Ts05), then Reco of both daytime and nighttime was calculated respectively by the function. The major results are: (i) Derived from the Michaelis-Menten equation, the apparent quantum yield ( α) was 0.0027±0.0011 mgCO 2·μmol ?1 photons, and the maximum photosynthetic assimilation rate ( Amax) was 1.102±0.288 mgCO 2·m ?2·s ?1. Indistinctive seasonal variation of α or Amax was consistent with weak seasonal dynamics of leaf area index ( LAf) in such a lower subtropical evergreen mixed forest, (ii) Monthly accumulated Reco was estimated as 95.3±21.1 gC·m ?2mon ?1, accounting for about 68% of the gross primary product ( GPP). Monthly accumulated WEE was estimated as ?43.2±29.6 gC·m ?2·mon ?1. The forest ecosystem acted as carbon sink all year round without any seasonal carbon efflux period. Annual NEE of 2003 and 2004 was estimated as ?563.0 and ?441.2 gC·m ?2·a ?1 respectively, accounting for about 32% of GPP. 相似文献
17.
Estimates of greenhouse gas evasion from rivers have been refined over the past decades to constrain their role in global carbon cycle processes. However, despite 55% of the human population living in urban areas, urban rivers have had limited attention. We monitored carbon dynamics in an urbanized river (River Kelvin, 331 km 2, UK) to explore the drivers of dissolved carbon lateral and vertical export. Over a 2-year sampling period, riverine methane (CH 4) and carbon dioxide (CO 2) concentrations were consistently oversaturated with respect to atmospheric equilibria, leading to continual degassing to the atmosphere. Carbon stable isotopic compositions (δ 13C) indicated that terrestrially derived carbon comprised most of the riverine CH 4 and dissolved CO 2 (CO 2*) load while dissolved inorganic carbon (DIC) from groundwater was the main form of riverine DIC. The dynamics of CH 4, CO 2*, and DIC in the river were primarily hydrology-controlled, that is, [CH 4] and [CO 2*] both increased with elevated discharge, total [DIC] decreased with elevated discharge while the proportion of biologically derived DIC increased with increasing discharge. The concentration of dissolved organic carbon (DOC) showed a weak relationship with river hydrology in summer and autumn and was likely influenced by the combined sewer overflows. Carbon emission to the atmosphere is estimated to be 3.10 ± 0.61 kg C·m −2·yr −1 normalized to water surface area, with more than 99% emitted as CO 2. Annual carbon loss to the coastal estuary is approximately 4.69 ± 0.70 Gg C yr −1, with annual DIC export approximately double that of DOC. Per unit area, the River Kelvin was a smaller carbon source to the atmosphere than natural rivers/streams but shows elevated fluxes of DIC and DOC under comparable conditions. This research illustrates the role urban systems may have on riverine carbon dynamics and demonstrates the potential tight link between urbanization and riverine carbon export. 相似文献
18.
Many studies on global climate have forecast major changes in the amounts and spatial patterns of precipitation that may significantly affect temperate grasslands in arid and semi-arid regions. As a part of ChinaFLUX, eddy covariance flux measurements were made at a semi-arid Leymus chinensis steppe in Inner Mongolia, China during 2003–2004 to quantify the response of carbon exchange to environmental changes. Results showed that gross ecosystem production ( F GEP) and ecosystem respiration ( R eco) of the steppe were significantly depressed by water stress due to lack of precipitation during the growing season. Temperature was the dominant factor affecting F GEP and R eco in 2003, whereas soil moisture imposed a significant influence on both R eco and F GEP in 2004. Under wet conditions, R eco showed an exponentially increasing trend with temperature ( Q 10 = 2.0), but an apparent reduction in the value of R eco and its temperature sensitivity were observed during the periods of water stress ( Q 10=1.6). Both heat and water stress can cause decrease in F GEP. The seasonality of ecosystem carbon exchange was strongly correlated with the variation of precipitation. With less precipitation in 2003, the steppe sequestrated carbon in June and July, and went into a senescence in early August due to water stress. As compared to 2003, the severe drought during the spring of 2004 delayed the growth of the steppe until late June, and the steppe became a CO 2 sink from early July until mid-September, with ample precipitation in August. The semi-arid steppe released a total of 9.7 g C·m ?2 from May 16 to the end of September 2003, whereas the net carbon budget during the same period in 2004 was close to zero. Long-term measurements over various grasslands are needed to quantify carbon balance in temperate grasslands. 相似文献
19.
An open-path eddy covariance system was set up in Damxung rangeland station to measure the carbon flux from July to October, 2003. The canopy quantum yield ( α) of alpine meadow was calculated by the linear function between the net ecosystem carbon dioxide exchange (NEE) and the photosynthetic active radiation (PAR) under low light, and how it was influenced by the temperature was also discussed. Results showed that the canopy α decreased almost linearly with temperature, with the decrease in every 1 °C increase of temperature similar to those measured on leaf level of C 3 plant. At the beginning, the decrease of canopy α with temperature was 0.0005 μmol CO 2·μmol ?1 PAR; while it increased to 0.0008 μmol CO 2·μmol ?1 PAR in September, showing a rising trend with plant growing stages. Compared with the canopy α calculated with rectangular hyperbola function, the value in the paper was lower. However, the method advanced here has the advantages in examining the relationship between α and the key environmental factors, such as temperature. 相似文献
20.
Understanding the exchange processes of energy and carbon dioxide (CO 2) in the soil–vegetation–atmosphere system is important for assessing the role of the terrestrial ecosystem in the global water and carbon cycle and in climate change. We present a soil–vegetation–atmosphere integrated model (ChinaAgrosys) for simulating energy, water and CO 2 fluxes, crop growth and development, with ample supply of nutrients and in the absence of pests, diseases and weed damage. Furthermore, we test the hypotheses of whether there is any significant difference between simulations over different time steps. CO 2, water and heat fluxes were estimated by the improving parameterization method of the coupled photosynthesis–stomatal conductance–transpiration model. Soil water evaporation and plant transpiration were calculated using a multilayer water and heat‐transfer model. Field experiments were conducted in the Yucheng Integrated Agricultural Experimental Station on the North China Plain. Daily weather and crop growth variables were observed during 1998–2001, and hourly weather variables and water and heat fluxes were measured using the eddy covariance method during 2002–2003. The results showed that the model could effectively simulate diurnal and seasonal changes of net radiation, sensible and latent heat flux, soil heat flux and CO 2 fluxes. The processes of evapotranspiration, soil temperature and leaf area index agree well with the measured values. Midday depression of canopy photosynthesis could be simulated by assessing the diurnal change in canopy water potential. Moreover, the comparisons of simulated daily evapotranspiration and net ecosystem exchange (NEE) under different time steps indicated that time steps used by a model affect the simulated results. There is no significant difference between simulated evapotranspiration using the model under different time steps. However, simulated NEE produces large differences in the response to different time steps. Therefore, the accurate calculation of average absorbed photosynthetic active radiation is important for the scaling of the model from hourly steps to daily steps in simulating energy and CO 2 flux exchanges between winter wheat and the atmosphere. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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