鼎湖山针阔叶混交林冠层下方CO2通量及其环境响应

精确估算典型森林生态系统冠层下方CO₂通量（Fcb）对验证陆地生态系统碳平衡模型具有重要意义。采用开路涡度相关法对鼎湖山针阔叶混交林Fcb进行定位测定,根据1周年数据分析Fcb及其对环境要素的响应特征,结果表明：(1) 白天Fcb呈下降趋势表明地表植被全年具有光合能力,但总体上地表植被和土壤表现为CO2排放源;(2) Van’t Hoff方程、Arrhenius方程和Lloyd-Taylor方程均可以较好反映土壤温度(Ts)与Fcb的关系,其中仅Lloyd-Talor方程能够反映温度因子敏感性指标Q10随温度的变异性特征;(3) Lloyd-Talor方程模拟的Fcb完全由Ts控制,而连乘模型由Ts和土壤水分(Ms)控制,可以反映水热条件的综合影响,对Fcb具有更强的拟合能力;(4)在Ms较大时连乘模型对Fcb的估算高于Lloyd-Talor方程,反之在干旱时段连乘模型模拟结果低于Lloyd-Talor方程,表明当存在水分胁迫时,Ms可以成为影响Fcb的主导因子;(5) 2003年鼎湖山针阔叶混交林Fcb总量((787.4±296.8)gCm^-2a^-1)比静态箱-气相色谱法测得的土壤呼吸偏低17%。与箱式法相比,涡度相关法通量测定结果普遍存在偏低估算现象。     

二氧化碳储存通量对森林生态系统碳收支的影响

涡度相关系统观测高度以下的CO₂储存通量对准确评价森林生态系统与大气间净CO₂交换量（NEE）有着重要的影响.本研究以长白山阔叶红松林为研究对象,利用2003年的涡度相关观测数据以及CO₂浓度廓线数据,分析了CO₂储存通量的变化规律及其对碳收支过程的影响.结果表明：涡度相关观测高度以下的CO₂储存通量具有典型的日变化特征,其最大变化量出现在大气稳定与不稳定层结转换期.利用涡度相关系统观测的单点CO₂浓度变化方法与利用CO₂浓度廓线方法计算的CO₂储存通量差异不显著.忽略CO₂储存通量,在半小时尺度上会造成对夜间和白天的NEE分别低估25%和19%,在日和年尺度上,会对NEE低估10%和25%;忽略CO₂储存通量,会低估Michaelis-Menten光响应方程及Lloyd-Taylor呼吸方程的参数,并且对表观初始量子效率α和参考呼吸R_ref的低估最大;忽略CO₂储存通量,在半小时、日及年尺度上,均会对总光合作用（GPP）和生态系统呼吸（R_e）低估约20%.     

Ecosystem respiration and its controlling factors in a coniferous and broad-leaved mixed forest in Dinghushan, China

Accurate estimation of ecosystem respiration (R_eco) in forest ecosysteM_s is critical for validating terrestrial carbon models. Continuous eddy covariance measuremenT_s of R_eco were conducted in a coniferous and broad-leaved mixed forest located in Dinghushan Nature Reserve of southern China. R_eco was estimated and the controlling environmental factors were analyzed based on two years' data from 2003 to 2004. Major resulT_s included that: (1) R_eco was affected by soil temperature, soil moisture, canopy air temperature and humidity, where soil temperature at 5 cm depth was the dominant factor. (2) The exponential equation, Van't Hoff equation, Arrhenius equation and Lyold-Talor equation can be used to describe the relationship between R_eco and temperature factors with similar statistical significance, while Lyold-Talor equation was the most sensitive to the temperature index (Q₁₀). (3) The multiplicative model driven by soil temperature (T_s) and soil moisture (M_s) was more corresponsive to R_eco, which explained that there were more R_eco variations than Lyold-Talor equation, both for higher and lower M_s. However, there was no statistical difference between the two models. (4) Annually accumulated R_eco of the mixed forest in 2003 was estimated as 1100–1135.6 gC m^?2 a^?1 by using daytime data, which was 12%–25% higher than R_eco (921–975 gC m^?2 a^?1) estimated by using nighttime data. The resulT_s suggested that using daytime data to estimate R_eco can avoid the common underestimation problem caused by using eddy covariance methods. The study provides a basic method for further study on accurate estimation of net ecosystem CO₂ exchange (NEE) in the coniferous and broad-leaved mixed forest in southern China.     

Soil CO2 efflux in contrasting boreal deciduous and coniferous stands and its contribution to the ecosystem carbon balance

Similar nonsteady‐state automated chamber systems were used to measure and partition soil CO₂ efflux in contrasting deciduous (trembling aspen) and coniferous (black spruce and jack pine) stands located within 100 km of each other near the southern edge of the Boreal forest in Canada. The stands were exposed to similar climate forcing in 2003, including marked seasonal variations in soil water availability, which provided a unique opportunity to investigate the influence of climate and stand characteristics on soil CO₂ efflux and to quantify its contribution to the net ecosystem CO₂ exchange (NEE) as measured with the eddy‐covariance technique. Partitioning of soil CO₂ efflux between soil respiration (including forest‐floor vegetation) and forest‐floor photosynthesis showed that short‐ and long‐term temporal variations of soil CO₂ efflux were related to the influence of (1) soil temperature and water content on soil respiration and (2) below‐canopy light availability, plant water status and forest‐floor plant species composition on forest‐floor photosynthesis. Overall, the three stands were weak to moderate sinks for CO₂ in 2003 (NEE of ?103, ?80 and ?28 g C m^?2 yr^?1 for aspen, black spruce and jack pine, respectively). Forest‐floor respiration accounted for 86%, 73% and 75% of annual ecosystem respiration, in the three respective stands, while forest‐floor photosynthesis contributed to 11% and 14% of annual gross ecosystem photosynthesis in the black spruce and jack pine stands, respectively. The results emphasize the need to perform concomitant measurements of NEE and soil CO₂ efflux at longer time scales in different ecosystems in order to better understand the impacts of future interannual climate variability and vegetation dynamics associated with climate change on each component of the carbon balance.     

Radon fluxes in tropical forest ecosystems of Brazilian Amazonia: night-time CO2 net ecosystem exchange derived from radon and eddy covariance methods

Radon‐222 (Rn‐222) is used as a transport tracer of forest canopy–atmosphere CO₂ exchange in an old‐growth, tropical rain forest site near km 67 of the Tapajós National Forest, Pará, Brazil. Initial results, from month‐long periods at the end of the wet season (June–July) and the end of the dry season (November–December) in 2001, demonstrate the potential of new Rn measurement instruments and methods to quantify mass transport processes between forest canopies and the atmosphere. Gas exchange rates yield mean canopy air residence times ranging from minutes during turbulent daytime hours to greater than 12 h during calm nights. Rn is an effective tracer for net ecosystem exchange of CO₂ (CO₂ NEE) during calm, night‐time hours when eddy covariance‐based NEE measurements are less certain because of low atmospheric turbulence. Rn‐derived night‐time CO₂ NEE (9.00±0.99 μmol m^?2 s^?1 in the wet season, 6.39±0.59 in the dry season) was significantly higher than raw uncorrected, eddy covariance‐derived CO₂ NEE (5.96±0.51 wet season, 5.57±0.53 dry season), but agrees with corrected eddy covariance results (8.65±1.07 wet season, 6.56±0.73 dry season) derived by filtering out lower NEE values obtained during calm periods using independent meteorological criteria. The Rn CO₂ results suggest that uncorrected eddy covariance values underestimate night‐time CO₂ loss at this site. If generalizable to other sites, these observations indicate that previous reports of strong net CO₂ uptake in Amazonian terra firme forest may be overestimated.     

Response of soil respiration to simulated N deposition in a disturbed and a rehabilitated tropical forest in southern China

Responses of soil respiration (CO₂ emission) to simulated N deposition were studied in a disturbed (reforested forest with previous understory and litter harvesting) and a rehabilitated (reforested forest with no understory and litter harvesting) tropical forest in southern China from October 2005 to September 2006. The objectives of the study were to test the following hypotheses: (1) soil respiration is higher in rehabilitated forest than in disturbed forest; (2) soil respiration in both rehabilitated and disturbed tropical forests is stimulated by N additions; and (3) soil respiration is more sensitive to N addition in disturbed forest than in rehabilitated forest due to relatively low soil nutrient status in the former, resulting from different previous human disturbance. Static chamber and gas chromatography techniques were employed to quantify the soil respiration, following different N treatments (Control, no N addition; Low-N, 5 g N m⁻² year⁻¹; Medium-N, 10 g N m⁻² year⁻¹), which had been applied continuously for 26 months before the respiration measurement. Results showed that soil respiration exhibited a strong seasonal pattern, with the highest rates observed in the hot and wet growing season (April–September) and the lowest rates in winter (December–February) in both rehabilitated and disturbed forests. Soil respiration rates exhibited significant positive exponential relationship with soil temperature and significant positive linear relationship with soil moisture. Soil respiration was also significantly higher in the rehabilitated forest than in the disturbed forest. Annual mean soil respiration rate in the rehabilitated forest was 20% lower in low-N plots (71 ± 4 mg CO₂-C m⁻² h⁻¹) and 10% lower in medium-N plots (80 ± 4 mg CO₂-C m⁻² h⁻¹) than in the control plots (89 ± 5 mg CO₂-C m⁻² h⁻¹), and the differences between the control and low-N or medium-N treatments were statistically significant. In disturbed forest, annual mean soil respiration rate was 5% lower in low-N plots (63 ± 3 mg CO₂-C m⁻² h⁻¹) and 8% lower in medium-N plots (61 ± 3 mg CO₂-C m⁻² h⁻¹) than in the control plots (66 ± 4 mg CO₂-C m⁻² h⁻¹), but the differences among treatments were not significant. The depressed effects of experimental N deposition occurred mostly in the hot and wet growing season. Our results suggest that response of soil respiration to elevated N deposition in the reforested tropical forests may vary depending on the status of human disturbance. Responsible Editor: Hans Lambers.     

基于涡度协方差法和生理生态法对落叶松林CO2通量的初步研究

 该文利用涡度协方差法和生理生态学方法（不同分量的累积和）获得的通量观测数据,对老山落叶松(Larix gmelinii)林(45°20′N, 127°34 ′E)的碳收支进行了分析。通过对每0.5 h所测数据进行的分析表明,能量平衡达到75％,说明涡度协方差法适应于本站的研究。较阴天气情况 下,林分光照利用效率显著高于晴朗天气,可能归因于阴天较多的散射光。以单位土地面积计算发现,通过涡度协方差法计算的落叶松林生态 系统的总初级生产力在20～50 μmol•m^-2•s^-1之间,远高于冠层叶片的总光合速率9.8～23.4μmol•m^-2•s^-1 (平均值16.2μmol•m^-2•s^-1 ),而 当综合考虑冠层光合和林下植物光合作用时,两种方法测定结果吻合性较好,说明林下植物对落叶松林碳平衡有重要影响。在估计森林生态系 统呼吸方面,以有风夜晚净生态系统交换量（NEE）来代表生态系统呼吸总量（3～9μmol•m^-2•s^-1）低估了生态系统呼吸总量,粗略估计较生 理生态学方法（不同呼吸分量的累积和）低估了50%左右（14.2μmol•m^-2•s^-1）。结果发现两种方法在估计森林碳平衡方面存在一定的差异, 呼吸量的估计差异应是今后研究的重点。     

腾格里荒漠红砂-珍珠群落CO2收支变化及其不同观测方法间的比较

由于荒漠生态系统植被覆盖度低、生产力低下,其在全球碳循环中的作用被长期忽视。为探讨荒漠生态系统碳收支各组分的变化规律,以腾格里荒漠红砂(Reaumuria soongorica Maxim.)-珍珠(Salsola passerina Beg.)群落为研究对象,采用静态箱式法研究了该群落的净生态系统CO2交换量(NEE)、生态系统呼吸、土壤呼吸的日变化规律,同时将该方法所获得的NEE结果与涡动相关法观测的结果进行了比较。结果表明:(1)红砂-珍珠群落NEE的日变化表现为,在6:00—9:00左右出现一个CO2吸收的高峰值,随后在12:00—15:00左右出现一个CO2释放高峰值。红砂种群、珍珠种群和整个群落NEE的平均值分别为0.018、0.020和0.028 mg CO2m-2s-1;(2)红砂种群、珍珠种群、土壤及整个群落生态系统呼吸速率的日变化规律一致,均表现为明显的单峰变化趋势,在12:00—15:00左右出现一个CO2释放的高峰值。红砂种群、珍珠种群、土壤和整个群落的生态系统呼吸的平均值分别为:0.121、0.062、0.029和0.040 mg CO2m-2s-1。以盖度为加权因子计算得到红砂种群、珍珠种群和土壤呼吸占生态系统呼吸的比例分别为:9%、21%和70%,由此可见,生态系统呼吸主要来源于土壤呼吸。(3)将箱式法和涡动相关法观测的NEE进行比较,结果表明两种方法观测的NEE变化规律基本一致,相关系数达到0.7。采用箱式法观测的NEE高于涡动相关法观测的结果,平均值分别0.028 mg CO2m-2s-1(箱式法)和0.015 mg CO2m-2s-1(涡动相关法),涡动相关法的观测结果与箱式法观测结果的比值为0.54。综上可得,荒漠生态系统土壤呼吸的变化速率决定了生态系统呼吸的变化规律,采用箱式法可能高估了荒漠生态系统CO2的释放量。     

Base Cation Cycling in a Pristine Watershed of the Canadian Boreal Forest

In forest ecosystems the single largest respiratory flux influencing net ecosystem productivity (NEP) is the total soil CO₂ efflux; however, it is difficult to make measurements of this flux that are accurate at the ecosystem scale. We examined patterns of soil CO₂ efflux using five different methods: auto-chambers, portable gas analyzers, eddy covariance along and two models parameterized with the observed data. The relation between soil temperature and soil moisture with soil CO₂ effluxes are also investigated, both inter-annually and seasonally, using these observations/results. Soil respiration rates (R _soil) are greatest during the growing season when soil temperatures are between 15 and 25 °C, but some soil CO₂ efflux occurs throughout the year. Measured soil respiration was sensitive to soil temperature, particularly during the spring and fall. All measurement methods produced similar annual estimates. Depending on the time of the year, the eddy covariance (flux tower) estimate for ecosystem respiration is similar to or slightly lower than estimates of annual soil CO₂ efflux from the other methods. As the eddy covariance estimate includes foliar and stem respiration which the other methods do not; it was expected to be larger (perhaps 15–30%). The auto-chamber system continuously measuring soil CO₂ efflux rates provides a level of temporal resolution that permits investigation of short- to longer term influences of factors on these efflux rates. The expense of building and maintaining an auto chamber system may not be necessary for those researchers interested in estimating R _soil annually, but auto-chambers do allow the capture of data from all seasons needed for model parameterization.     

Soil respiration in Pinus tabulaeformis forest during dormant period at Huoditang forest zone in the Qinling Mountains, China

Soil CO₂ efflux in forest ecosystems during dormant season is one of the key components of the forest ecosystem carbon balance. Little work has been done to quantify soil CO₂ efflux in most forests in China in special time because of difficulty in taking measurements. Soil respiration in a natural secondary Pinus tabulaeformis forest at Huoditang in the Qinling Mountains was measured from October to December in 2006 by means of open-path dynamic chamber technique. Relationships of soil respiration rate (R_s) with mean soil temperature (MST) and mean volumetric soil moisture content (MVSC) in different depths (0-5 cm and 5-10 cm) were examined in the current study. We found that (1) At the same observation site (upper-part, middle-part or under-part), there were tremendous temporal and spatial variations in R_s with variation coefficients of 48.38%, 82.51% and 81.88% in October, November and December, respectively; (2) There was a significant exponent relationship between diurnal mean soil respiration rate (F_c) and diurnal mean soil temperature (DMST) when DMST > 8.5°C for both soil depths (0-5 cm and 5-10 cm) examined. The temperature sensitivity of soil respiration, known as the Q₁₀ value, was 1.297 and 1.323 in soil depths of 0-5 cm and 5-10 cm, respectively; (3) Relationship between R_s and MVSC was complex in soil depths of 0-5 cm and 5-10 cm; (4) Soil CO₂ efflux from October to December in 2006 in the experimental area was (977.37 ± 88.43) to (997.19 ± 80.73) gCm⁻² (p = 0.005).     

Rates of Litter Decomposition and Soil Respiration in Relation to Soil Temperature and Water in Different-Aged Pinus massoniana Forests in the Three Gorges Reservoir Area,China

To better understand the soil carbon dynamics and cycling in terrestrial ecosystems in response to environmental changes, we studied soil respiration, litter decomposition, and their relations to soil temperature and soil water content for 18-months (Aug. 2010–Jan. 2012) in three different-aged Pinus massoniana forests in the Three Gorges Reservoir Area, China. Across the experimental period, the mean total soil respiration and litter respiration were 1.94 and 0.81, 2.00 and 0.60, 2.19 and 0.71 µmol CO₂ m⁻² s⁻¹, and the litter dry mass remaining was 57.6%, 56.2% and 61.3% in the 20-, 30-, and 46-year-old forests, respectively. We found that the temporal variations of soil respiration and litter decomposition rates can be well explained by soil temperature at 5 cm depth. Both the total soil respiration and litter respiration were significantly positively correlated with the litter decomposition rates. The mean contribution of the litter respiration to the total soil respiration was 31.0%–45.9% for the three different-aged forests. The present study found that the total soil respiration was not significantly affected by forest age when P. masonniana stands exceed a certain age (e.g. >20 years old), but it increased significantly with increased soil temperature. Hence, forest management strategies need to protect the understory vegetation to limit soil warming, in order to reduce the CO₂ emission under the currently rapid global warming. The contribution of litter decomposition to the total soil respiration varies across spatial and temporal scales. This indicates the need for separate consideration of soil and litter respiration when assessing the climate impacts on forest carbon cycling.     

Effects of soil water content on soil respiration in forests and cattle pastures of eastern Amazonia

The effect of soil water content on efflux of CO₂ from soils has been described by linear, logarithmic, quadratic, and parabolic functions of soil water expressed as matric potential, gravimetric and volumetric water content, water holding capacity, water-filled pore space, precipitation indices, and depth to water table. The effects of temperature and water content are often statistically confounded. The objectives of this study are: (1) to analyze seasonal variation in soil water content and soil respiration in the eastern Amazon Basin where seasonal temperature variation is minor; and (2) to examine differences in soil CO₂ emissions among primary forests, secondary forests, active cattle pastures, and degraded cattle pastures. Rates of soil respiration decreased from wet to dry seasons in all land uses. Grasses in the active cattle pasture were productive in the wet season and senescent in the dry season, resulting in the largest seasonal amplitude of CO₂ emissions, whereas deep-rooted forests maintained substantial soil respiration during the dry season. Annual emissions were 2.0, 1.8, 1.5, and 1.0 kg C m^-2 yr^-1 for primary forest, secondary forest, active pasture, and degraded pasture, respectively. Emissions of CO₂ were correlated with the logarithm of matric potential and with the cube of volumetric water content, which are mechanistically appropriate functions for relating soil respiration at below-optimal water contents. The parameterization of these empirical functions was not consistent with those for a temperate forest. Relating rates of soil respiration to water and temperature measurements made at some arbitrarily chosen depth of the surface horizons is simplistic. Further progress in defining temperature and moisture functions may require measurements of temperature, water content and CO₂ production for each soil horizon.     

Annual cycles of water vapour and carbon dioxide fluxes in and above a boreal aspen forest

Water vapour and CO₂ fluxes were measured using the eddy correlation method above and below the overstorey of a 21-m tall aspen stand in the boreal forest of central Saskatchewan as part of the Boreal Ecosystem-Atmosphere Study (BOREAS). Measurements were made at the 39.5-m and 4-m heights using 3-dimensional sonic anemometers (Kaijo-Denki and Solent, respectively) and closed-path gas analysers (LI-COR 6262) with 6-m and 4.7-m long heated sampling tubing, respectively. Continuous measurements were made from early October to mid-November 1993 and from early February to late-September 1994. Soil CO₂ flux (respiration) was measured using a LI-COR 6000-09 soil chamber and soil evaporation was measured using Iysimetry. The leaf area index of the aspen and hazelnut understorey reached 1.8 and 3.3, respectively. The maximum daily evapotranspiration (E) rate was 5–6 mm d^?1. Following leaf-out the hazelnut and soil accounted for 22% of the forest E. The estimated total E was 403 mm for 1994. About 88% of the precipitation in 1994 was lost as evapotranspiration. During the growing season, the magnitude of half-hourly eddy fluxes of CO₂ from the atmosphere into the forest reached 1.2 mg CO₂ m^?2 s^?1 (33 μmol C m^?2 s^?1) during the daytime. Downward eddy fluxes at the 4-m height were observed when the hazelnut was growing rapidly in June and July. Under well-ventilated night-time conditions, the eddy fluxes of CO₂ above the aspen and hazelnut, corrected for canopy storage, increased exponentially with soil temperature at the 2-cm depth. Estimates of daytime respiration rates using these relationships agreed well with soil chamber measurements. During the 1994 growing season, the cumulative net ecosystem exchange (NEE) was -3.5 t C ha^?1 y^?1 (a net gain by the system). For 1994, cumulative NEE, ecosystem respiration (R) and gross ecosystem photosynthesis (GEP = R - NEE) were estimated to be -1.3, 8.9 and 10.2 t C ha^?1 y^?1 respectively. Gross photosynthesis of the hazelnut was 32% of GEP.     

Comparison of soil respiration methods in a mid-latitude deciduous forest

In forest ecosystems the single largest respiratory flux influencing net ecosystem productivity (NEP) is the total soil CO₂ efflux; however, it is difficult to make measurements of this flux that are accurate at the ecosystem scale. We examined patterns of soil CO₂ efflux using five different methods: auto-chambers, portable gas analyzers, eddy covariance along and two models parameterized with the observed data. The relation between soil temperature and soil moisture with soil CO₂ effluxes are also investigated, both inter-annually and seasonally, using these observations/results. Soil respiration rates (R _soil) are greatest during the growing season when soil temperatures are between 15 and 25 °C, but some soil CO₂ efflux occurs throughout the year. Measured soil respiration was sensitive to soil temperature, particularly during the spring and fall. All measurement methods produced similar annual estimates. Depending on the time of the year, the eddy covariance (flux tower) estimate for ecosystem respiration is similar to or slightly lower than estimates of annual soil CO₂ efflux from the other methods. As the eddy covariance estimate includes foliar and stem respiration which the other methods do not; it was expected to be larger (perhaps 15–30%). The auto-chamber system continuously measuring soil CO₂ efflux rates provides a level of temporal resolution that permits investigation of short- to longer term influences of factors on these efflux rates. The expense of building and maintaining an auto chamber system may not be necessary for those researchers interested in estimating R _soil annually, but auto-chambers do allow the capture of data from all seasons needed for model parameterization.     

CO2 flux from soil in pastures and forests in southwestern Amazonia

Stocks of carbon in Amazonian forest biomass and soils have received considerable research attention because of their potential as sources and sinks of atmospheric CO₂. Fluxes of CO₂ from soil to the atmosphere, on the other hand, have not been addressed comprehensively in regard to temporal and spatial variations and to land cover change, and have been measured directly only in a few locations in Amazonia. Considerable variation exists across the Amazon Basin in soil properties, climate, and management practices in forests and cattle pastures that might affect soil CO₂ fluxes. Here we report soil CO₂ fluxes from an area of rapid deforestation in the southwestern Amazonian state of Acre. Specifically we addressed (1) the seasonal variation of soil CO₂ fluxes, soil moisture, and soil temperature; (2) the effects of land cover (pastures, mature, and secondary forests) on these fluxes; (3) annual estimates of soil respiration; and (4) the relative contributions of grass‐derived and forest‐derived C as indicated by δ¹³CO₂. Fluxes were greatest during the wet season and declined during the dry season in all land covers. Soil respiration was significantly correlated with soil water‐filled pore space but not correlated with temperature. Annual fluxes were higher in pastures compared with mature and secondary forests, and some of the pastures also had higher soil C stocks. The δ¹³C of CO₂ respired in pasture soils showed that high respiration rates in pastures were derived almost entirely from grass root respiration and decomposition of grass residues. These results indicate that the pastures are very productive and that the larger flux of C cycling through pasture soils compared with forest soils is probably due to greater allocation of C belowground. Secondary forests had soil respiration rates similar to mature forests, and there was no correlation between soil respiration and either forest age or forest biomass. Hence, belowground allocation of C does not appear to be directly related to the stature of vegetation in this region. Variation in seasonal and annual rates of soil respiration of these forests and pastures is more indicative of flux of C through the soil rather than major net changes in ecosystem C stocks.     

神农架海拔梯度上4种典型森林的土壤呼吸组分及其对温度的敏感性

量化森林土壤呼吸及其组分对温度的响应对准确评估未来气候变化背景下陆地生态系统的碳平衡极其重要。该文通过对神农架海拔梯度上常绿阔叶林、常绿落叶阔叶混交林、落叶阔叶林以及亚高山针叶林4种典型森林土壤呼吸的研究发现: 4种森林类型的年平均土壤呼吸速率和年平均异养呼吸速率分别为1.63、1.79、1.74、1.35 μmol CO₂·m^-2·s^-1和1.13、1.12、1.12、0.80 μmol CO₂·m^-2·s^-1。该地区的土壤呼吸及其组分呈现出明显的季节动态, 夏季最高, 冬季最低。4种森林类型中, 阔叶林的土壤呼吸显著高于针叶林, 但阔叶林之间的土壤呼吸差异不显著。土壤温度是影响土壤呼吸及其组分的主要因素, 二者呈显著的指数关系; 土壤含水量与土壤呼吸之间没有显著的相关关系。4种典型森林土壤呼吸的Q₁₀值分别为2.38、2.68、2.99和4.24, 随海拔的升高土壤呼吸对温度的敏感性增强, Q₁₀值随海拔的升高而增加。     

Contribution of root respiration to total soil respiration in a Japanese cedar (Cryptomeria japonica D. Don) artificial forest

Soil respiration was measured for 2 years in an artificial gap and in an undisturbed area in a Japanese cedar (Cryptomeria japonica D. Don) forest to estimate the contribution of root respiration to total soil respiration. Measurement plots were set up at the center of the gap, the edge of the gap, the edge of the surrounding stand and within the stand. Using a small gap (2.5 m × 2.5 m) enabled us to maintain the same soil temperature and soil moisture as found in the stand. Seasonal fluctuations in soil respiration, increasing in summer and decreasing in winter, corresponded to changes in the soil surface temperature. Soil respiration in the gap site did not differ significantly from those in the stand in the first year of gap formation. However, in the second year, the minimum CO₂ flux was observed at the center of the gap and the maximum at the edge of the surrounding stand. Assuming that the differences between soil respiration in the center of the gap and that in the stand were equal to the root respiration, the root respiration rate was calculated from the relationship between the root respiration rates (Rr) and the soil surface temperature (Ts) by Ln(Rr) = 0.07Ts + 3.48. The average contribution of root respiration to total soil respiration, as estimated from the soil surface temperature in the stand by using the above equation, was 49%. After taking root decomposition into consideration, the contribution of root respiration to soil respiration increased from 49 to 57%.     

模拟氮沉降和降雨对华西雨屏区常绿阔叶林土壤呼吸的影响

从2013年12月至2014年11月,通过野外原位试验,对华西雨屏区常绿阔叶林进行了模拟氮沉降和降雨试验,采用LI-8100土壤碳通量分析系统(LI-COR Inc.,USA)测定了对照(CK)、氮沉降(N)、减雨(R)、增雨(W)、氮沉降+减雨(NR)、氮沉降+增雨(NW)6个处理水平的土壤呼吸速率,并通过回归方程分析了温度和湿度与土壤呼吸速率间的关系。结果表明:(1)氮沉降和增雨抑制了常绿阔叶林土壤呼吸速率,减雨促进了常绿阔叶林土壤呼吸速率。(2)减雨使华西雨屏区常绿阔叶林土壤呼吸年通量增加了258 g/m~2,而模拟氮沉降和增雨使华西雨屏区常绿阔叶林土壤呼吸年通量分别减少了321g/m~2和406g/m~2。(3)减雨增加了土壤呼吸的温度敏感性,模拟氮沉降和增雨降低了土壤呼吸的温度敏感性。(4)模拟温度和湿度与土壤呼吸速率间回归方程分析表明,土壤水分对土壤呼吸速率的影响较小。(5)模拟氮沉降和增雨处理减少土壤微生物生物量碳、氮的含量,减雨处理增加了土壤微生物生物量碳、氮的含量。(6)模拟氮沉降和降雨对华西雨屏区土壤CO_2释放的影响未表现出明显的交互作用。     

Soil CO2 efflux in a beech forest: comparison of two closed dynamic systems

The aim of this study was to understand why two closed dynamic systems with a very similar design gave large differences in soil CO₂ efflux measurements (PP systems and LI-COR). Both in the field (forest beech stand) and in the laboratory, the PPsystems gave higher estimations of soil CO₂ efflux than the LI-COR system (ranging from 30% to 50%). The difference in wind speed occurring within the soil respiration chambers (0.9 m s⁻¹ within the SRC-1 and 0.4 m s⁻¹ within the LI-6000-09 chambers) may account for the discrepancy between the two systems. An excessive air movement inside the respiration chamber is thought to disrupt the high laminar boundary layer over the forest floor. This would promote an exhaust of the CO₂ accumulated into the upper soil layers into the chamber and a lateral diffusion of CO₂ in the soil towards the respiration chamber. The discrepancy between the two systems was reduced (i) by decreasing fan speed within the SRC-1, (ii) by increasing wind speed over the soil surface outside the respiration chamber, or (iii) by using an artificial soil design without high CO₂ concentration in soil pores. We show that wind speed is an important component of soil CO₂ diffusion which must be taken into account when measuring soil CO₂ efflux, even on very fine textured soil like silt-loam soil. Proper measurement can be achieved by maintaining wind speed inside the chamber below 0.4 m s⁻¹ since low wind speed conditions predominate under forest canopies. However, more accurate measurements will be obtained by regulating wind speeds within the chamber at a velocity representative of the wind speed recorded simultaneously at the floor surface. This revised version was published online in June 2006 with corrections to the Cover Date.     

Evaluation of methods for estimating soil carbon dioxide efflux across a gradient of forest disturbance

Better understanding of variation in soil carbon dioxide (CO₂) efflux caused by measurement techniques is needed, especially over gradients of site disturbance, to accurately estimate the global carbon cycle. We present soil CO₂ efflux data from a gradient of disturbance to ponderosa pine (Pinus ponderosa C. Lawson var. scopulorum Engelm.) forests in northern Arizona, USA that were obtained using four different techniques: vented static chambers, a Licor 6400‐09, and soil CO₂ diffusion profiles using two different models (Moldrup, Millington–Quirk) to estimate soil gas diffusivity. We also compared soil CO₂ efflux measured by the Moldrup and Millington–Quirk diffusion profile methods to nighttime total ecosystem respiration (TER) data from an eddy covariance tower. We addressed four questions: (1) Does the use of a given method to measure soil CO₂ efflux bias results across a disturbance gradient? (2) Does the magnitude of difference between observed and modeled estimates of soil CO₂ differ between methods and across sites? (3) What is the spatial variability of each method at each site? (4) Which method is closest to the estimate of TER measured by the eddy covariance tower? Although soil CO₂ efflux varied significantly among methods the differences were consistent among sites. Measured and modeled total growing season fluxes were generally higher for the Licor 6400‐09 and Millington–Quirk diffusion gradient methods compared with static chamber and the Moldrup diffusion gradient methods. A power analysis showed that the larger static chamber was the most efficient method at sampling spatial variation in soil CO₂ efflux. Nighttime measurements of soil CO₂ efflux from the Moldrup diffusion gradient method were most strongly related to nighttime TER assessed with eddy covariance. The use of a single, well‐implemented method to measure soil CO₂ efflux is unlikely to create bias in comparisons across a gradient of forest disturbance.