碳同位素技术在森林生态系统碳循环研究中的应用

碳同位素技术对碳素在生态系统中的迁移动态具有很好的示踪作用,在生态学各领域研究中应用广泛。土壤、大气、植物是森林生态系统的重要碳库,植物是大气和土壤交换碳元素的重要介质。本文简要总结了碳同位素技术在研究碳元素在植物体内以及植物、土壤、大气碳库之间的迁移规律和生态学过程中的应用,展望了该技术在森林界面学中的应用前景。     

Partitioning net ecosystem carbon exchange and the carbon isotopic disequilibrium in a subalpine forest

We investigate the utility of an improved isotopic method to partition the net ecosystem exchange of CO₂ (F) into net photosynthesis (F_A) and nonfoliar respiration (F_R). Measurements of F and the carbon isotopic content in air at a high‐elevation coniferous forest (the Niwot Ridge AmeriFlux site) were used to partition F into F_A and F_R. Isotopically partitioned fluxes were then compared with an independent flux partitioning method that estimated gross photosynthesis (GEE) and total ecosystem respiration (TER) based on statistical regressions of night‐time F and air temperature. We compared the estimates of F_A and F_R with expected canopy physiological relationships with light (photosynthetically active radiation) and air temperature. Estimates of F_A and GEE were dependent on light as expected, and TER, but not F_R, exhibited the expected dependence on temperature. Estimates of the isotopic disequilibrium D , or the difference between the isotopic signatures of net photosynthesis (δ_A, mean value ?24.6‰) and ecosystem respiration (δ_R, mean value ?25.1‰) were generally positive (δ_A>δ_R). The sign of D observed here is inconsistent with many other studies. The key parameters of the improved isotopic flux partitioning method presented here are ecosystem scale mesophyll conductance (g_m) and maximal vegetative stomatal conductance (g_cmax). The sensitivity analyses of F_A, F_R, and D to g_cmax indicated a critical value of g_cmax (0.15 mol m^?2 s^?1) above which estimates of F_A and F_R became larger in magnitude relative to GEE and TER. The value of D decreased with increasing values of g_m and g_cmax, but was still positive across all values of g_m and g_cmax. We conclude that the characterization of canopy‐scale mesophyll and stomatal conductances are important for further progress with the isotope partitioning method, and to confirm our anomalous isotopic disequilibrium findings.     

Leaf carbon isotope discrimination and nitrogen content for riparian trees along elevational transects

 Leaf carbon isotope discrimination (Δ), seasonal estimates of the leaf-to-air water vapor gradient on a molar basis (ω), and leaf nitrogen contents were examined in three riparian tree species (Populus fremontii, P. angustifolia, and Salix exigua) along elevational transects in northern and southern Utah USA (1500–2670 m and 600–1820 m elevational gradients, respectively). The ω values decreased with elevation for all species along transects. Plants growing at higher elevations exhibited lower Δ values than plants at lower elevations (P. fremontii, 22.9‰ and 19.5‰, respectively; P. angustifolia, 23.2‰ and 19.2‰, respectively; and S.␣exigua, 21.1‰ and 19.1‰, respectively). Leaf nitrogen content increased with elevation for all species, suggesting that photosynthetic capacity at a given intercellular carbon dioxide concentration was greater at higher elevations. Leaf Δ and nitrogen content values were highly correlated, implying that leaves with higher photosynthetic capacities also had lower intercellular carbon dioxide concentrations. No significant interannual differences were detected in carbon isotope discrimination. Received: 25 February 1996 / Accepted: 8 September 1996     

Tracing carbon and oxygen isotope signals from newly assimilated sugars in the leaves to the tree-ring archive

The analysis of δ ¹³C and δ ¹⁸O in tree-ring archives offers retrospective insights into environmental conditions and ecophysiological processes. While photosynthetic carbon isotope discrimination and evaporative oxygen isotope enrichment are well understood, we lack information on how the isotope signal is altered by downstream metabolic processes.
In Pinus sylvestris , we traced the isotopic signals from their origin in the leaf water ( δ ¹⁸O) or the newly assimilated carbon ( δ ¹³C), via phloem sugars to the tree-ring, over a time-scale that ranges from hours to a growing season.
Seasonally, variable ¹³C enrichment of sugars related to phloem loading and transport did lead to uncoupling between δ ¹³C in the tree-ring, and the c _i/ c _a ratio at the leaf level. In contrast, the oxygen isotope signal was transferred from the leaf water to the tree-ring with an expected enrichment of 27‰, with time-lags of approximately 2 weeks and with a 40% exchange between organic oxygen and xylem water oxygen during cellulose synthesis.
This integrated overview of the fate of carbon and oxygen isotope signals within the model tree species P. sylvestris provides a novel physiological basis for the interpretation of δ ¹³C and δ ¹⁸O in tree-ring ecology.     

Modeling dynamics of stable carbon isotopic exchange between a boreal forest ecosystem and the atmosphere

Stable isotopes of CO₂ contain unique information on the biological and physical processes that exchange CO₂ between terrestrial ecosystems and the atmosphere. In this study, we developed an integrated modeling system to simulate dynamics of stable carbon isotope of CO₂, as well as moisture, energy, and momentum, between a boreal forest ecosystem and the atmosphere, as well as their transport/mixing processes through the convective boundary layer (CBL), using remotely sensed surface parameters to characterize the surface heterogeneity. It has the following characteristics: (i) it accounts for the influences of the CBL turbulent mixing and entrainment of the air aloft; (ii) it scales individual leaf‐level photosynthetic discrimination up to the whole canopy (Δ_canopy) through the separation of sunlit and shaded leaf groups; (iii) it has the capacity to examine the detailed interrelationships among plant water‐use efficiency, isotope discrimination, and vapor pressure deficit; and (iv) it has the potential to investigate how an ecosystem discriminates against ¹³C at various time and spatial scales. The monthly mean isotopic signatures of ecosystem respiration (i.e. δ¹³C_R) used for isotope flux calculation are retrieved from the nighttime flask data from the intensive campaigns (1998–2000) at 20 m level on Fraserdale tower, and the data from the growing season in 1999 are used for model validation. Both the simulated CO₂ mixing ratio and δ¹³C of CO₂ at the 20 m level agreed with the measurements well in different phases of the growing season. On a diurnal basis, the greatest photosynthetic discrimination at canopy level (i.e. Δ_canopy) occurred early morning and late afternoon with a varying range of 10–26‰. The diurnal variability of Δ_canopy was also associated with the phases of growing season and meteorological variables. The annual mean Δ_canopy in 1999 was computed to be 19.58‰. The monthly averages of Δ_canopy varied between 18.55‰ and 20.84‰ with a seasonal peak during the middle growing season. Because of the strong opposing influences of respired and photosynthetic fluxes on forest air (both CO₂ and ¹³CO₂) on both the diurnal and seasonal time scales, CO₂ was consistently enriched with the heavier ¹³C isotope (less negative δ¹³C) from July to October and depleted during the remaining months, whereas on a diurnal basis, CO₂ was enriched with the heavier ¹³C in the late afternoon and depleted in early morning. For the year 1999, the model results reveal that the boreal ecosystem in the vicinity of Fraserdale tower was a small sink with net uptake of 29.07 g ¹²C m^?2 yr^?1 and 0.34 g ¹³C m^?2 yr^?1.     

氨基糖单体碳氮同位素的分析及其应用

氨基糖(AS)作为有机质中在分子水平识别的重要组分,研究其来源与转化能更好地认知微生物对有机质的调控作用。作为一种新兴技术,氨基糖单体同位素分析(CSIA-AS)为研究氨基糖各组分在自然环境中的变化特征提供了更详细的信息。本文系统总结了CSIA-AS技术的测定方法及其在氨基糖循环转化研究中的应用,气相色谱-同位素比值质谱法(GC-IRMS)和离子色谱-同位素比值质谱法(IC-IRMS)作为2种主要的氨基糖同位素测定方法,各有利弊,但进行相应的校正后均可实现可靠的测定结果。氨基糖各组分在土壤有机质中具有相对较低的周转时间,细菌来源的胞壁酸相对葡萄糖胺、半乳糖胺和甘露糖胺具有更高的矿化速率。氨基糖在环境中的来源和代谢转化受底物的影响,这与微生物群落对不同碳、氮源的特异性响应有关。CSIA-AS技术的推广需要进一步的方法优化并将其与微生物甄别等其他手段相结合,以此来更好地阐释有机质的来源、转化和归宿及其调控机制。     

Carbon isotope discrimination indicates improving water-use efficiency of trees in northern Eurasia over the last 100 years

We investigated the response of conifer trees in northern Eurasia to climate change and increasing CO₂ over the last century by measuring the carbon isotope ratio in tree rings. Samples from Larix, Pinus and Picea trees growing at 26 high‐latitude sites (59–71°N) from Norway to Eastern Siberia were analysed. When comparing the periods 1861–1890 and 1961–1990, the isotope discrimination and the ratio of the intercellular to ambient CO₂ concentration (c_i/c_a) remained constant for trees growing in mild oceanic climate and under extremely cold and dry continental conditions. This shows a strong coordination of gas‐exchange processes, consisting in a biochemical acclimation and a reduction of the stomatal conductance. The correlation for c_i/c_a between the two investigated periods was particularly strong for Larix (r²=0.90) and Pinus (r²=0.94), but less pronounced for Picea (r²=0.47). Constant c_i/c_a under increasing CO₂ in the atmosphere resulted in improved intrinsic water‐use efficiency (W_i), the amount of water loss at the leaf level per unit carbon gain. We found that 125 out of 126 trees showed increasing W_i from 1861 to 1890 to 1961 to 1990, with an average improvement of 19.2±0.9% (mean±SE). The adaptation in gas exchange and reduced transpiration of trees growing in this region must have had a strong impact on the water and energy budget, resulting in a drier and warmer surface air layer today than would exist without this vegetation–climate feedback.     

碳同位素示踪技术及其在陆地生态系统碳循环研究中的应用与展望

碳同位素示踪技术具有高度的专一性和灵敏度, 经过几十年的发展, 形成了一系列成熟的标记方法, 在陆地生态系统碳循环过程的研究中已得到广泛应用。目前, 自然丰度法、与¹³C贫化示踪技术结合的自由空气中气体浓度增加(FACE)实验、脉冲与连续标记法以及碳同位素高丰度底物富集标记法是研究陆地生态系统碳循环过程常用的碳同位素示踪方法; 通过将长期定位实验和室内模拟实验结合, 量化光合碳在植物-土壤系统的传输与分配特征, 明确植物光合碳对土壤有机质的来源、稳定化过程的影响及其微生物驱动机制; 阐明土壤碳动态变化(迁移与转化)和新碳与老碳对土壤碳库储量的相对贡献, 评估有机碳输入、转化与稳定的生物与非生物微观界面过程机制。然而, 生态系统碳循环受气候、植被、人为活动等多因素影响, 碳同位素技术需要结合质谱、光谱技术实现原位示踪, 结合分子生物学技术阐明其微生物驱动机制, 从而构建灵敏、准确、多尺度、多方位的同位素示踪技术体系。因此, 该文以稳定碳同位素为主, 综述了碳同位素示踪技术的原理、分析方法和在陆地生态系统碳循环过程中的应用进展, 归纳总结了碳同位素示踪技术结合原位检测技术和分子生物学技术的研究进展和应用前景, 并对碳同位素示踪技术存在的问题进行了分析和展望。     

沙棘属植物叶片碳稳定同位素含量与气候的关系

本试验以131个沙棘属植物种群为研究对象,通过测定其叶片碳稳定同位素(δ13C)值,分析了碳稳定同位素特征与环境因子之间的关系.结果 表明:沙棘属植物叶片的δ13C值介于-24.65‰～-29.11‰‰,平均值为-26.97‰,属于C3植物,叶片δ13C值变异系数为种内大于种间,表明环境因子是影响沙棘属植物叶片δ13C...     

Carbon balance in the tundra, boreal forest and humid tropical forest during climate change: scaling up from leaf physiology and soil carbon dynamics

Carbon exchange by the terrestrial biosphere is thought to have changed since pre-industrial times in response to increasing concentrations of atmospheric CO₂ and variations (anomalies) in inter-annual air temperatures. However, the magnitude of this response, particularly that of various ecosystem types (biomes), is uncertain. Terrestrial carbon models can be used to estimate the direction and size of the terrestrial responses expected, providing that these models have a reasonable theoretical base. We formulated a general model of ecosystem carbon fluxes by linking a process-based canopy photosynthesis model to the Rothamsted soil carbon model for biomes that are not significantly affected by water limitation. The difference between net primary production (NPP) and heterotrophic soil respiration (R_h) represents net ecosystem production (NEP). The model includes (i) multiple compartments for carbon storage in vegetation and soil organic matter, (ii) the effects of seasonal changes in environmental parameters on annual NEP, and (iii) the effects of inter-annual temperature variations on annual NEP. Past, present and projected changes in atmospheric CO₂ concentration and surface air temperature (at different latitudes) were analysed for their effects on annual NEP in tundra, boreal forest and humid tropical forest biomes. In all three biomes, annual NEP was predicted to increase with CO₂ concentration but to decrease with warming. As CO₂ concentrations and temperatures rise, the positive carbon gains through increased NPP are often outweighed by losses through increased R_h, particularly at high latitudes where global warming has been (and is expected to be) most severe. We calculated that, several times during the past 140 years, both the tundra and boreal forest biomes have switched between being carbon sources (annual NEP negative) and being carbon sinks (annual NEP positive). Most recently, significant warming at high latitudes during 1988 and 1990 caused the tundra and boreal forests to be net carbon sources. Humid tropical forests generally have been a carbon sink since 1960. These modelled responses of the various biomes are in agreement with other estimates from either field measurements or geochemical models. Under projected CO₂ and temperature increases, the tundra and boreal forests will emit increasingly more carbon to the atmosphere while the humid tropical forest will continue to store carbon. Our analyses also indicate that the relative increase in the seasonal amplitude of the accumulated NEP within a year is about 0–14% year^?1 for boreal forests and 0–23% year^?1 in the tundra between 1960 and 1990.     

亚热带地区马尾松树干呼吸碳同位素组成的时间变化特征及其控制因子

作为森林生态系统碳循环的重要组成部分,树干呼吸的时空变异性直接决定着全球碳库对气候变化的响应和反馈。然而,目前关于树干呼吸的时间变化特征,尤其是树干呼吸碳同位素组成(δ¹³C)变化的控制机理还存在很大的不确定性。为探明树干呼吸及其碳同位素的时间变化特征,采用气室法并利用基于光腔衰荡光谱(CRDS)技术组装的Picarro观测系统,于2018年8月—2019年10月对6棵马尾松进行树干呼吸及其同位素的监测,同时测定树干液流速率和树干温度。结果表明:(1)树干呼吸速率及其δ¹³C值均不存在明显的日变化模式,且与树干液流、树干温度相关性不显著;(2)树干呼吸速率季节变化趋势明显,变化范围为0.08～1.61μmol·m^-2·s^-1,且树干温度解释了树干呼吸速率季节变化的82%;(3)树干呼吸δ¹³C呈现先升高后下降的季节变化模式,非生长季的平均δ¹³C为-23.25‰±0.91‰,显著高于生长季的-27.93‰±0.25‰。研究表明,树干呼吸及其碳同位素组成在不...     

马占相思人工林净二氧化碳交换和碳同位素通量

应用稳定碳同位素技术,对马占相思人工林冠层受光和遮荫叶片的碳同化率(A_net)和叶面积指数(L)进行加权,将叶片水平的¹³C甄别率(Δ_i)扩展至冠层光合甄别率(Δ_canopy),测定光合固定和呼吸释放的碳同位素通量及其净交换通量.结果表明：Δ_canopy的日变化明显,日出前和中午出现较低值(18.47‰和19.87‰),而日落前达到最大(21.21‰);秋季末期(11月)至翌年夏季,Δ_canopy逐步升高,年平均为(20.37±0.29)‰.不同季节自养呼吸(日间叶片呼吸除外)和异养呼吸释放CO₂的碳同位素比率(δ¹³C)平均值分别为(-28.70±0.75)‰和(-26.75±1.3)‰,春季林冠夜间呼吸CO₂的δ¹³C最低(-30.14‰),秋季末期最高(-28.01‰).马占相思林与大气的CO₂碳同位素通量在春季和夏季中午时峰值分别为178.5和217 μmol·m^-2 ·s^-1·‰,日均值分别为638.4 和873.2 μmol·m^-2·s^-1·‰.冠层叶片吸收CO₂的碳同位素通量较呼吸释出CO₂的碳同位素通量高1.6～2.5倍,表明马占相思林日间吸收大量CO₂,降低空气CO₂浓度,具有改善环境的良好生态服务功能.     

Importance of short-term dynamics in carbon isotope ratios of ecosystem respiration (delta13C(R)) in a Mediterranean oak woodland and linkage to environmental factors

Temporal dynamics in carbon isotope ratios of ecosystem respiration (delta13C(R)) were evaluated on hourly, daily and annual timescales in a Mediterranean woodland. Emphasis was given to the periods of transition from wet to dry season and vice versa, when the system turns from a net carbon sink to a source. The constancy of nocturnal delta13C(R) was tested. The relationship between delta13C(R) (determined through Keeling plots) and environmental factors was evaluated through time-lag analysis. Delta13C(R) exhibited high annual variation (> 7). During the transition periods, delta13C(R) correlated significantly with factors influencing photosynthetic discrimination, soil respiration, and whole-canopy conductance. Time-lags differed between below- and above-ground variables, and between seasons. A shift in regression parameters with environmental factors indicated seasonal differences in ecosystem responsiveness (e.g. temperature acclimation). Delta13C(R) exhibited substantial nocturnal enrichment (> 4) from dusk to dawn. These data indicate pronounced short-term dynamics in delta13C(R) at hourly to daily timescales and a modulated response to environmental drivers. Substantial short-term changes in nocturnal delta13C(R) may have important implications for the sampling protocols of nocturnal Keeling plots.     

模拟冻融环境下亚高山森林凋落物分解速率及有机碳动态

森林凋落物分解是森林生态系统物质循环的重要环节,季节性冻融交替是影响凋落物分解的重要环境因素之一,但不同林型的凋落物对冻融响应的差异性很少被量化。为了解冻融环境对森林凋落物分解进程的影响,以川西亚高山森林地区阔叶林、针叶林和针阔混交林3种典型林型的凋落物为实验材料,从凋落物基质质量、冻融环境等影响凋落分解的因素着手,采用模拟冻融循环过程（-5-5℃）,研究了冻融循环中3种林型凋落物分解速率和有机碳含量的动态变化。结果发现,3中典型林型凋落物经过不同冻融处理后,其质量损失、质量损失速率均存在显著差异（P<0.05）。混交林凋落物和针叶林凋落物的分解速率呈慢-快-慢的趋势,而阔叶林凋落物的分解速率逐渐减小。在冻融循环处理下,3种林型的凋落物碳绝对含量呈波动下降的趋势,说明微生物固定外源碳和凋落物释放碳间存在动态平衡。相同林型的凋落物在不同冻融处理下,有机碳释放有显著差异（P<0.05）。其中,冻融环境显著（P<0.05）促进了混交林凋落物和针叶林凋落物有机碳的释放,但是对阔叶林凋落物有机碳的释放没有起到促进作用。这表明全球气候变暖情景下,亚高山森林土壤冻融事件频发将加快凋落物的分解,但变化程度受到凋落物质量控制。     

Combining meteorology, eddy fluxes, isotope measurements, and modeling to understand environmental controls of carbon isotope discrimination at the canopy scale

Estimates of terrestrial carbon isotope discrimination are useful to quantify the terrestrial carbon sink. Carbon isotope discrimination by terrestrial ecosystems may vary on seasonal and interannual time frames, because it is affected by processes (e.g. photosynthesis, stomatal conductance, and respiration) that respond to variable environmental conditions (e.g. air humidity, temperature, light). In this study, we report simulations of the temporal variability of canopy‐scale C₃ photosynthetic carbon isotope discrimination obtained with an ecophysiologically based model (ISOLSM) designed for inclusion in global models. ISOLSM was driven by half‐hourly meteorology, and parameterized with eddy covariance measurements of carbon and energy fluxes and foliar carbon isotope ratios from a pine forest in Metolius (OR). Comparing simulated carbon and energy fluxes with observations provided a range of parameter values that optimized the simulated fluxes. We found that the sensitivity of photosynthetic carbon isotope discrimination to the slope of the stomatal conductance equation (m, Ball–Berry constant) provided an additional constraint to the model, reducing the wide parameter space obtained from the fluxes alone. We selected values of m that resulted in similar simulated long‐term discrimination as foliar isotope ratios measured at the site. The model was tested with ¹³C measurements of ecosystem (δ_R) and foliar (δ_f) respiration. The daily variability of simulated ¹³C values of assimilated carbon (δ_A) was similar to that of observed δ_f, and higher than that of observed and simulated δ_R. We also found similar relationships between environmental factors (i.e. vapor pressure deficit) and simulated δ_R as measured in ecosystem surveys of δ_R. Therefore, ISOLSM reasonably simulated the short‐term variability of δ_A controlled by atmospheric conditions at the canopy scale, which can be useful to estimate the variability of terrestrial isotope discrimination. Our study also shows that including the capacity to simulate carbon isotope discrimination, together with simple ecosystem isotope measurements, can provide a useful constraint to land surface and carbon balance models.     

Use of decreasing foliar carbon isotope discrimination during water limitation as a carbon tracer to study whole plant carbon allocation

Foliar carbon isotope discrimination (Δ) of C₃ plants decreases in water‐deficit situations as discrimination by the photosynthetic primary carboxylation reaction decreases. This diminished Δ in leaves under water deficit can be used as a tracer to study whole plant carbon allocation patterns. Carbon isotope composition (δ¹³C value) of leaf hot water extracts or leaf tissue sap represents a short‐term integral of leaf carbon isotope discrimination and thus represents the δ¹³C value of source carbon that may be distributed within a plant in water‐deficit situations. By plotting the δ¹³C values of source carbon against the δ¹³C values of sink tissues, such as roots or stems, it is possible to assess carbon allocation to and incorporation into sink organs in relation to already present biomass. This natural abundance labelling method has been tested in three independent experiments, a one‐year field study with the fruit tree species Ziziphus mauritiana and peach (Prunus persica), a medium‐term drought stress experiment with Ziziphus rotundifolia trees in the glasshouse, and a short‐term drought stress experiment with soybean (Glycine max). The data show that the natural abundance labelling method can be applied to qualitatively assess carbon allocation in drought‐stressed plants. Although it is not possible to estimate exact fluxes of assimilated carbon during water deficit the method represents an easy to use tool to study integrated plant adaptations to drought stress. In addition, it is a less laborious method that can be applied in field studies as well as in controlled experiments, with plants from any developmental stage.     

Carbon isotopic tracing of sugars throughout whole‐trees exposed to climate warming

Trees allocate C from sources to sinks by way of a series of processes involving carbohydrate transport and utilization. Yet these dynamics are not well characterized in trees, and it is unclear how these dynamics will respond to a warmer world. Here, we conducted a warming and pulse‐chase experiment on Eucalyptus parramattensis growing in a whole‐tree chamber system to test whether warming impacts carbon allocation by increasing the speed of carbohydrate dynamics. We pulse‐labelled large (6‐m tall) trees with ¹³C‐CO₂ to follow recently fixed C through different organs by using compound‐specific isotope analysis of sugars. We then compared concentrations and mean residence times of individual sugars between ambient and warmed (+3°C) treatments. Trees dynamically allocated ¹³C‐labelled sugars throughout the aboveground‐belowground continuum. We did not, however, find a significant treatment effect on C dynamics, as sugar concentrations and mean residence times were not altered by warming. From the canopy to the root system, ¹³C enrichment of sugars decreased, and mean residence times increased, reflecting dilution and mixing of recent photoassimilates with older reserves along the transport pathway. Our results suggest that a locally endemic eucalypt was seemingly able to adjust its physiology to warming representative of future temperature predictions for Australia.     

碳稳定同位素技术在植物水分胁迫研究中的应用

植物体的碳稳定同位素组成主要由植物本身的生物学特性决定 ,但环境胁迫对其影响也十分明显。综述了碳稳定同位素技术在研究植物水分利用效率、生物量高低及判断历史气候依据等研究领域的进展 ,阐明了植物体的 δ1 3C值对干旱、盐分及其它环境因素的变化所引起的水分胁迫的响应 ,并对碳稳定同位素对水分胁迫的响应机理进行了归纳和推断     

Environmental controls over carbon exchange of three forest ecosystems in eastern China

Net ecosystem productivity (NEP) was continuously measured using the eddy covariance (EC) technique from 2003 to 2005 at three forest sites of ChinaFLUX. The forests include Changbaishan temperate mixed forest (CBS), Qianyanzhou subtropical coniferous plantation (QYZ), and Dinghushan subtropical evergreen broad‐leaved forest (DHS). They span wide ranges of temperature and precipitation and are influenced by the eastern Asian monsoon climate to varying extent. In this study, we estimated ecosystem respiration (RE) and gross ecosystem productivity (GEP). Comparison of ecosystem carbon exchange among the three forests shows that RE was mainly determined by temperature, with the forest at CBS exhibiting the highest temperature sensitivity among the three ecosystems. The RE was highly dependent on GEP across the three forests, and the ratio of RE to GEP decreased along the North–South Transect of Eastern China (NSTEC) (i.e. from the CBS to the DHS), with an average of 0.77 ± 0.06. Daily GEP was mainly influenced by temperature at CBS, whereas photosynthetic photon flux density was the dominant factor affecting the daily GEP at both QYZ and DHS. Temperature mainly determined the pattern of the interannual variations of ecosystem carbon exchange at CBS. However, water availability primarily controlled the interannual variations of ecosystem carbon exchange at QYZ. At DHS, NEP attained the highest values at the beginning of the dry seasons (autumn) rather than the rainy seasons (summer), probably because insufficient radiation and frequent fog during the rainy seasons hindered canopy photosynthesis. All the three forest ecosystems acted as a carbon sink from 2003 to 2005. The annual average values of NEP at CBS, QYZ, and DHS were 259 ± 19, 354 ± 34, and 434 ± 66 g C m⁻² yr⁻¹, respectively. The slope of NEP that decreased with increasing latitude along the NSTEC was markedly different from that observed on the forest transect in the European continent. Long‐term flux measurements over more forest ecosystems along the NSTEC will further help verify such a difference between the European forest transect and the NSTEC and provide insights into the responses of ecosystem carbon exchange to climate change in China.