科尔沁草地不同大气稳定度下湍流特征谱分析

利用科尔沁半干旱风沙草原区涡度相关观测数据,计算并分析了不同大气稳定度条件下湍流的功率谱和协谱.结果表明:经向风速与纬向风速的功率谱在大气不稳定层结、近中性层结、稳定层结条件下谱形均相似,并遵循-2/3定律;近中性层结条件下垂直风速的功率谱没有惯性子区,此时仪器对脉动信号的捕捉不够完全,稳定层结条件下垂直风速功率谱表明观测层产生了泄流和平流;CO_2和H_2O浓度的功率谱分析表明,红外气体分析仪对高频信号的响应能力能够满足实际观测的需要,其功率谱的谱峰随大气稳定度的增强而向高频转移;垂直风速与3种标量的协谱谱形相似,不同大气稳定度下协谱惯性子区长度随大气稳定度的增强而变短,且均符合-4/3定律,说明三维超声风速仪与红外气体分析仪的空间间隔不会对通量观测结果造成显著影响.     

人工林冠层的湍流微气象特征

利用涡动相关系统测定黄河小浪底森林生态系统定位研究站人工林在萌芽期(2015年3月15日至4月15日,春季)和叶片成型期(2015年7月15日至8月15日,夏季)的微气象数据,分析了冠层湍流微气象特征、湍流强度、湍流风速标准差和总体输送系数,旨在深入了解森林生态系统的微气象特征,为进一步研究能量平衡与物质交换提供工作基础.结果表明: 冠层湍流谱在低频部分具有峰值频率,惯性副区具有明显的耗散趋势,基本符合-5/3规律.冠层结构对湍流强度影响明显,春季湍流旺盛时,风速小于3 m·s^-1,而夏季时风速小于2 m·s^-1.湍流风速标准差符合1/3次幂相似规律,且水平方向比垂直方向的拟合效果好.冠层风速在u、v、w 3个方向分量的风速标准差与摩擦风速比值在春季为2.55、2.06和1.30,在夏季为2.61、2.45和1.21.总体输送系数随稳定度的增加而逐渐减小,在不稳定层结和稳定层结条件下可相差1～2个量级,冠层结构对各方向的湍流风速具有直接影响,从而改变物质能量在冠层的扩散方向.     

长白山阔叶红松林二氧化碳湍流交换特征

采用开路式涡度相关技术,研究了长白山阔叶红松林森林-大气界面的CO₂湍流交换特征.结果表明,在近中性大气层结条件下,冠层上方垂直风速和CO₂浓度功率谱在惯性子区基本符合-2/3定律,垂直方向主导湍涡尺度约为40 m.湍流通量贡献区主要在0.01～2 Hz频率范围内,冠层上方低频传输的湍涡贡献了更多的CO₂通量.这说明开路式涡度相关仪器系统可以满足冠层上方湍流通量观测的基本要求.但通过涡度相关法实测获得的森林-大气CO₂通量仍存在夜间低估现象,非湍流过程的增加是涡度相关技术应用的主要制约因素.因此,需要对弱湍流条件下的CO₂通量做相应的修订.     

栓皮栎人工林冠层温度变化特征及其与微气象因子的关系

基于2011年栓皮栎主要生长季(5-8月)的冠层温度数据及同步观测得到的冠层微气象资料,分析了典型晴天和阴天条件下华北低丘山地栓皮栎人工林冠层温度(Tc)的变化特征及其与微气象因子的关系.结果表明:晴天日9:00-16:00,栓皮栎人工林林冠边界层处于不稳定状态,Tc比空气温度(Ta)平均高3.55℃;阴天日Tc的变化较晴天条件下平缓;Tc与Ta、净辐射(Rn)、相对湿度、风速等冠层微气象要素的复相关达极显著水平,其复相关系数为0.825;影响Tc的主要气象因子是Ta和Rn,二者对Tc的影响程度与天气状况有关.     

苹果树冠层空气温差变化及其与环境因子的关系

于2002—2005年,采用红外测温仪观测得到苹果树主要生长季节冠层温度数据,结合同步观测得到冠层净辐射(Rn)、风速(V)、空气温度(Ta)和湿度(RH)等冠层微气象要素数据及0～80cm土壤含水量(SW),分析苹果树冠层-空气温差(△T)变化规律及其与环境因子的关系.结果表明:苹果树主要生长季节(萌芽期—果实迅速膨大期)晴天△T日变化呈多峰曲线分布,△T最高值都出现在12:00—13:00左右;阴天△T日变化呈多峰曲线分布,但△T绝对值明显低于晴天日.2003年和2004年晴天日14:00△T与Rn、V、RH及SW具有较好的复相关关系:ΔT=7.159-0.002Rn-0.061V-0.7RH-46.0SW(r=-0.825),与Rn、RH、V及SW的偏相关系数分别为0.125、-0.078、-0.036和-0.874,逐步回归方程式为ΔT=5.317-43.1SW,说明土壤水分对△T的影响程度相对最大.经2002年和2005年观测数据验证,△T观测值与计算值吻合关系较好,二者线性相关系数可达0.9083.这说明采用晴天日14:00时刻数据分析△T的影响机制,预测土壤水分含量具有很好的可行性.     

西双版纳热带季节雨林林冠上方湍流谱特征

利用中国陆地生态系统通量观测网络(ChinaFLUX)西双版纳热带森林通量观测站涡度相关方法测定的热带季节雨林林冠上方三维方向风速(u,v,w)以及CO2浓度、H2O浓度、气温等变量的10 Hz观测资料,选取1、4、7和10月4个代表性月份晴好天气,在全天5个不同时段内(8:00-11:30,12:00-15:00,15:30-19:00,19:30-23:30,0:00-7:30)求算了各要素的功率谱和与垂直风速的协谱,探讨了热带季节雨林林冠上方数据的高低频响应问题.结果表明:在热带季节雨林林冠上方,晴好天气且湍流条件良好状况下,6个变量的功率谱点阵曲线斜率在惯性副区内均满足-2/3定律;并且各要素与垂直风速的协谱点阵曲线斜率在惯性副区内满足-4/3定律.说明大尺度运动对物质和能量传输的贡献在高频率和中等强度频率信号范围内的响应能力能够满足观测所需要求,可以认为在复杂地形条件下西双版纳热带季节雨林进行通量测定的采样频率合理,所获得数据可以用来作为实际通量的结果加以使用.     

帽儿山地区森林冠层叶面积指数的地面观测与遥感反演

叶面积指数(leaf area index,LAI)是陆地生态系统最重要的结构参数之一,遥感和基于冠层孔隙率模型的光学仪器观测是快速获取LAI的有效方法,但由于植被叶片的聚集效应,这些方法通常只能获取有效叶面积指数(effective LAI,LAIe).本文以东北林业大学帽儿山实验林场为研究区,利用LAI2000观测森林冠层LAIe,并结合TRAC观测的叶片聚集度系数估算了森林冠层LAI,并通过分析基于Landsat5-TM数据计算的不同植被指数与LAIe之间的关系,建立了该区森林LAI遥感估算模型.结果表明:研究区阔叶林的LAI和LAIe基本相当,而针叶林的LAI比LAIe大27%;减化比值植被指数(reduced simple ratio,RSR)与该区LAIe的相关性最好(R2=0.763,n=23),最适合该区LAI的遥感提取.当海拔<400 m时,LAI随海拔高度的上升而快速增大;当海拔在400～750 m时,LAI随海拔高度的上升缓慢增大;当海拔>750 m时,LAI呈下降趋势.研究区森林冠层LAI与森林地上生物量存在显著的正相关关系.     

近地面激光雷达点云密度对森林冠层结构参数提取准确性的影响

基于激光雷达技术获取冠层结构为森林生态学研究增加了新的维度。搭载于多旋翼无人机的近地面激光雷达相比于固定翼有人机的机载激光雷达，能够更加灵活高效地获取森林群落样地高密度点云。但在实际操作中，往往出现局部低密度点云数据，影响了冠层结构参数提取的准确性。使用4块森林动态样地的近地面激光雷达点云数据；利用航带分解方法分析各样地低密度样方成因；采用点云抽稀模拟算法计算并拟合偏差曲线，对比不同样地、参数和取样尺度间的点云密度对冠层结构参数提取准确性的影响；根据偏差曲线计算各条件下保证参数提取准确性的最低点云密度。结果发现：1)低密度区域主要受地形或(和)近地面遥感设计规划的影响。地形复杂的测区(西双版纳和古田山样地),遥感规划难度大，整体难以获取高密度点云(在30点/m²左右),容易在沟谷和高海拔处出现低密度样方。平坦测区(长白山两块样地)虽可获取高密度点云(均超过150点/m²),但欠佳的遥感规划设计导致长白山1测区北部出现1hm²低密度区域。2)冠层参数提取准确性随点云密度减少而迅速降低，呈负指数幂函数关系。这一变化趋势在不同...     

辽西农林复合系统中杨树冠层导度特征

利用Granier热扩散式探针法对辽西杨树-玉米复合系统的杨树树干液流进行连续测定,并对环境因子(空气温度、空气湿度、净辐射、风速、土壤温度和土壤湿度)进行同步观测,结合Penman-Monteith方程计算冠层导度值.结果表明:研究区杨树冠层导度日变化呈“单峰型”曲线,季节变化表现为波动式下降趋势;冠层导度随着饱和水汽压差增加呈负对数下降,5-9月,冠层导度对水汽压差变化的敏感性逐渐下降;冠层导度与太阳辐射呈正相关关系;太阳辐射越大,冠层导度曲线下降幅度越大.不同月份,相同环境因子与冠层导度的相关程度不同.从整个生长季来看,与冠层导度相关性最显著的环境因子是饱和水汽压差.     

六盘山主要植被类型冠层截留特征

通过野外观测和模型模拟,研究了六盘山主要森林类型的冠层截留量、冠层截留容量和冠层截留模拟参数的变化.结果表明：六盘山主要森林类型的冠层截留率在8.59%～17.94%,穿透降雨率超过80%,树干茎流率在0.23%～3.10%;冠层截留容量在0.78～1.84 mm,其中叶截留容量在0.62～1.63 mm,枝干截留容量在0.13～0.29 mm,且针叶林的冠层截留容量高于阔叶林.考虑冠层叶面积指数的冠层截留改进模型较原有模型具有更好的模拟精度, 其中,研究区红桦林、华山松林、李灌丛和辽东栎-少脉椴混交林的模拟效果较好,辽东栎林、油松林和华西四蕊槭 石枣子灌丛模拟效果相对较差,这可能与冠层结构、叶面积指数以及降水特性等差异有关.     

Improving the clinical efficiency of T2 mapping of ligament integrity

Current MR methods use T₂^? relaxation time as a surrogate measure of ligament strength. Currently, a multi-echo voxel-wise least squares fit is the gold standard to create T₂^? maps; however, the post-processing is time-intensive and serves as a stopgap for clinical use. The study objective was to determine if an alternative method could improve post-processing time without sacrificing fidelity of T₂^? values for eventual translational use in the clinic. Using a 6 echo FLASH sequence, three different methods were used to determine intact posterior cruciate ligament (PCL) median T₂^? Two of these methods utilized a voxel-wise method to establish T₂^? maps: (1) a current “gold standard” method using a voxel-wise 6 echo least-squares fit (6LS) and (2) a voxel-wise 2 echo point T₂^? determination (2MM). The third method used median ligament signal intensity and a single nonlinear least-squares fit (6LS_ROI) instead of a voxel-wise basis. The resulting median T₂^? values of the PCL and computational time were compared. The median T₂^? values were 42% higher using the 2MM compared to the 6LS method (p<0.0001). However, a strong correlation was found for the median T₂^? values between the 2MM and 6LS methods (R²=0.80). The median T₂^? values were not significantly different between the 6LS and 6LS_ROI methods (p=0.519). Using the 2MM (which provides a regional map) and the 6LS_ROI (which efficiently provides the median T₂^? value) methods in tandem would take only minutes of post-processing computational time compared to the 6LS method (~540 min), and hence would facilitate clinical application of T₂^? maps to predict ligament structural properties as a patient outcome measure.     

Stomatal and pavement cell density linked to leaf internal CO2 concentration

Background and Aims

Stomatal density (SD) generally decreases with rising atmospheric CO₂ concentration, C_a. However, SD is also affected by light, air humidity and drought, all under systemic signalling from older leaves. This makes our understanding of how C_a controls SD incomplete. This study tested the hypotheses that SD is affected by the internal CO₂ concentration of the leaf, C_i, rather than C_a, and that cotyledons, as the first plant assimilation organs, lack the systemic signal.

Methods

Sunflower (Helianthus annuus), beech (Fagus sylvatica), arabidopsis (Arabidopsis thaliana) and garden cress (Lepidium sativum) were grown under contrasting environmental conditions that affected C_i while C_a was kept constant. The SD, pavement cell density (PCD) and stomatal index (SI) responses to C_i in cotyledons and the first leaves of garden cress were compared. ¹³C abundance (δ¹³C) in leaf dry matter was used to estimate the effective C_i during leaf development. The SD was estimated from leaf imprints.

Key Results

SD correlated negatively with C_i in leaves of all four species and under three different treatments (irradiance, abscisic acid and osmotic stress). PCD in arabidopsis and garden cress responded similarly, so that SI was largely unaffected. However, SD and PCD of cotyledons were insensitive to C_i, indicating an essential role for systemic signalling.

Conclusions

It is proposed that C_i or a C_i-linked factor plays an important role in modulating SD and PCD during epidermis development and leaf expansion. The absence of a C_i–SD relationship in the cotyledons of garden cress indicates the key role of lower-insertion CO₂ assimilation organs in signal perception and its long-distance transport.     

Modelling O2 and O2 unidirectional fluxes in plants. III: Fitting of experimental data by a simple model

Photosynthetic assimilation of CO₂ in plants results in the balance between the photochemical energy developed by light in chloroplasts, and the consumption of that energy by the oxygenation processes, mainly the photorespiration in C₃ plants. The analysis of classical biological models shows the difficulties to bring to fore the oxygenation rate due to the photorespiration pathway. As for other parameters, the most important key point is the estimation of the electron transport rate (ETR or J), i.e. the flux of biochemical energy, which is shared between the reductive and oxidative cycles of carbon. The only reliable method to quantify the linear electron flux responsible for the production of reductive energy is to directly measure the O₂ evolution by ¹⁸O₂ labelling and mass spectrometry. The hypothesis that the respective rates of reductive and oxidative cycles of carbon are only determined by the kinetic parameters of Rubisco, the respective concentrations of CO₂ and O₂ at the Rubisco site and the available electron transport rate, ultimately leads to propose new expressions of biochemical model equations. The modelling of ¹⁸O₂ and ¹⁶O₂ unidirectional fluxes in plants shows that a simple model can fit the photosynthetic and photorespiration exchanges for a wide range of environmental conditions. Its originality is to express the carboxylation and the oxygenation as a function of external gas concentrations, by the definition of a plant specificity factor Sp that mimics the internal reactions of Rubisco in plants. The difference between the specificity factors of plant (Sp) and of Rubisco (Sr) is directly related to the conductance values to CO₂ transfer between the atmosphere and the Rubisco site. This clearly illustrates that the values and the variation of conductance are much more important, in higher C₃ plants, than the small variations of the Rubisco specificity factor. The simple model systematically expresses the reciprocal variations of carboxylation and oxygenation exchanges illustrated by a “mirror effect”. It explains the protective sink effect of photorespiration, e.g. during water stress. The importance of the CO₂ compensation point, in classical models, is reduced at the benefit of the crossing points Cx and Ox, concentration values where carboxylation and oxygenation are equal or where the gross O₂ uptake is half of the gross O₂ evolution. This concept is useful to illustrate the feedback effects of photorespiration in the atmosphere regulation. The constancy of Sp and of Cx for a great variation of P under several irradiance levels shows that the regulation of the conductance maintains constant the internal CO₂ and the ratio of photorespiration to photosynthesis (PR/P). The maintenance of the ratio PR/P, in conditions of which PR could be reduced and the carboxylation increased, reinforces the hypothesis of a positive role of photorespiration and its involvement in the plant-atmosphere co-evolution.     

Extreme temperature tolerance of a hyperthermophilic protein coupled to residual structure in the unfolded state

Understanding the mechanisms that dictate protein stability is of large relevance, for instance, to enable design of temperature-tolerant enzymes with high enzymatic activity over a broad temperature interval. In an effort to identify such mechanisms, we have performed a detailed comparative study of the folding thermodynamics and kinetics of the ribosomal protein S16 isolated from a mesophilic (S16_meso) and hyperthermophilic (S16_thermo) bacterium by using a variety of biophysical methods. As basis for the study, the 2.0 Å X-ray structure of S16_thermo was solved using single wavelength anomalous dispersion phasing. Thermal unfolding experiments yielded midpoints of 59 and 111 °C with associated changes in heat capacity upon unfolding (ΔC_p⁰) of 6.4 and 3.3 kJ mol^− 1 K^− 1, respectively. A strong linear correlation between ΔC_p⁰ and melting temperature (T_m) was observed for the wild-type proteins and mutated variants, suggesting that these variables are intimately connected. Stopped-flow fluorescence spectroscopy shows that S16_meso folds through an apparent two-state model, whereas S16_thermo folds through a more complex mechanism with a marked curvature in the refolding limb indicating the presence of a folding intermediate. Time-resolved energy transfer between Trp and N-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-yl)methyl iodoacetamide of proteins mutated at selected positions shows that the denatured state ensemble of S16_thermo is more compact relative to S16_meso. Taken together, our results suggest the presence of residual structure in the denatured state ensemble of S16_thermo that appears to account for the large difference in quantified ΔC_p⁰ values and, in turn, parts of the observed extreme thermal stability of S16_thermo. These observations may be of general importance in the design of robust enzymes that are highly active over a wide temperature span.     

Seasonal variations in bulk tissue, fatty acid and monosaccharide δC values of leaves from mesotrophic grassland plant communities under different grazing managements

Leaves of 26 grass, herb, shrub and tree species were collected from mesotrophic grasslands to assess natural variability in bulk, fatty acid and monosaccharide δ¹³C values under different grazing management (cattle- or deer-grazed) on three sample dates (May, July and October) such that interspecific and spatiotemporal variations in whole leaf tissues and compound-specific δ¹³C values could be determined. The total mean leaf bulk δ¹³C value for plants was −28.9‰ with a range of values spanning 7.5‰. Significant interspecific variation between bulk leaf δ¹³C values was only determined in October (P = <0.001) when δ¹³C values of the leaf tissues from both sites was on average 1.5‰ depleted compared to during July and May. Samples from May were significantly different between fields (P = 0.03) indicating an effect from deer- or cattle-grazing in young leaves. The average individual monosaccharide δ¹³C value was 0.8‰ higher compared with whole leaf tissues. Monosaccharides were the most abundant components of leaf biomass, i.e. arabinose, xylose, mannose, galactose and glucose, and therefore, fluctuations in their individual δ¹³C values had a major influence on bulk δ¹³C values. An average depletion of ca. 1‰ in the bulk δ¹³C values of leaves from the deer-grazed field compared to the cattle-grazed field could be explained by a general depletion of 1.1‰ in glucose δ¹³C values, as glucose constituted >50% total leaf monosaccharides. In October, δ¹³C values of all monosaccharides varied between species, with significant variation in δ¹³C values of mannose and glucose in July, and mannose in May. This provided an explanation for the noted variability in the tissue bulk δ¹³C values observed in October 1999. The fatty acids C_16:0, C_18:2 and C_18:3 were highly abundant in all plant species. Fatty acid δ¹³C values were lower than those of bulk leaf tissues; average values of −37.4‰ (C_16:0), −37.0‰ (C_18:2) and −36.5‰ (C_18:3) were determined. There was significant interspecific variation in the δ¹³C values of all individual fatty acids during October and July, but only for C_18:2 in May (P = <0.05). This indicated that seasonal trends observed in the δ¹³C values of individual fatty acids were inherited from the isotopic composition of primary photosynthate. However, although wide diversity in δ¹³C values of grassland plants ascribed to grazing management, interspecific and spatiotemporal influences was revealed, significant trends (P = <0.0001) for fatty acid and monosaccharide δ¹³C values: δ¹³C_16:0 < δ¹³C_18:2 < δ¹³C_18:3 and δ¹³C_arabinose > δ¹³C_xylose > δ¹³C_glucose > δ¹³C_galactose, respectively, previously described, appear consistent across a wide range of species at different times of the year in fields under different grazing regimes.     

Synthesis and characterization of tetrairon-tungsten cluster complex containing a μ4, η-carbonyl ligand

Reaction of [(PPh₂C₅H₄)Cp₃Fe₄(CO)₄] (1) with (CO)₄W(CH₃CN)₂ at ambient temperature affords [(CO)₄W(PPh₂C₅H₄)Cp₃Fe₄(CO)₄] (2) as the major product, together with a small amount of [(CO)₅W(PPh₂C₅H₄)Cp₃Fe₄(CO)₄] (3). Compound 3 can be obtained in good yield by treating (CO)₅W(CH₃CN) with equal molar of 1, and reaction of 3 with Me₃NO in acetonitrile solvent produces 2 exclusively. The crystal structures of 2 and 3 have been determined by an X-ray diffraction study. Compound 2 contains an interesting μ₄, η²-CO ligand, where two electrons donated by the carbon atom are involved to bridge a Fe₃ face and two electrons from oxygen are donated to the tungsten(0) atom.     

N-acetoxy-N-acetylaminoarenes and nitrosoarenes one-electron non-enzymatic and enzymatic oxidation products of various carcinogenic aromatic acethydroxamic acids

A number of carcinogenic aromatic acethydroxamic acids (e.g.N-hydroxy-N-acetyl derivatives of 2-aminofluorene, 3-aminofluorene, 4-aminostilbene, 1-aminonaphthalene, 2-aminonaphthalene, 2-aminophenanthrene, and 4-aminobiphenyl) are readily oxidized by alkaline Fe(CN)₆³⁻ or Ag₂O. The free nitroxide radicals thus formed dismutate in organic solution according to second order kinetics to yield the corresponding N-acetoxy-N-acetylaminoarenes and nitrosoarenes. The structures of the latter products were established by mass and infrared spectrum analyses. Evicence was obtained for a similar one-electron oxidation of these acethydroxamic acids with horseradish peroxidase and H₂O₂ at pH 7. One-electron oxidation of N-hydroxy-2-acetylaminofluorene was also demonstrated with lactoperoxidase and human myeloperoxidase. The possible relevance of a similar peroxidative attack in vivo to the carcinogenic activities of some aromatic amines and amides is discussed.     

Robustness of central carbohydrate metabolism in developing maize kernels

The central carbohydrate metabolism provides the precursors for the syntheses of various storage products in seeds. While the underlying biochemical map is well established, little is known about the organization and flexibility of carbohydrate metabolic fluxes in the face of changing biosynthetic demands or other perturbations. This question was addressed in developing kernels of maize (Zea mays L.), a model system for the study of starch and sugar metabolism. ¹³C-labeling experiments were carried out with inbred lines, heterotic hybrids, and starch-deficient mutants that were selected to cover a wide range of performances and kernel phenotypes. In total, 46 labeling experiments were carried out using either [U-¹³C₆]glucose or [U-¹³C₁₂]sucrose and up to three stages of kernel development. Carbohydrate flux distributions were estimated based on glucose isotopologue abundances, which were determined in hydrolysates of starch by using quantitative ¹³C-NMR and GC-MS. Similar labeling patterns in all samples indicated robustness of carbohydrate fluxes in maize endosperm, and fluxes were rather stable in response to glucose or sucrose feeding and during development. A lack of ADP-glucose pyrophosphorylase in the bt2 and sh2 mutants triggered significantly increased hexose cycling. In contrast, other mutations with similar kernel phenotypes had no effect. Thus, the distribution of carbohydrate fluxes is stable and not determined by sink strength in maize kernels.     

Validation of the design of feeding experiments involving [(14)C]substrates used to monitor metabolic flux in higher plants

The aim of this study was to examine whether flux through the pathways of carbohydrate oxidation is accurately reflected in the pattern of ¹⁴CO₂ release from positionally labelled [¹⁴C]substrates in conventional radiolabel feeding studies. Heterotrophic cell suspension cultures of Arabidopsis thaliana were used for this work. The presence of an alkaline trap to capture metabolically generated ¹⁴CO₂ had no significant effect on the ratio of ¹⁴CO₂ release from specifically labelled [¹⁴C]substrates, or on the metabolism of [U-¹⁴C]glucose by the cells. Although the amount of ¹⁴CO₂ captured in a conventional time-course study was only about half of that released from a sample acidified at an equivalent time point, the ratios of ¹⁴CO₂ released from different positionally labelled [¹⁴C]glucose and [1-¹⁴C]gluconate were the same in untreated and acidified samples. Less than 5% of radioactivity supplied to the growth medium as [¹⁴C]bicarbonate was incorporated into acid-stable compounds, and there was no evidence for appreciable reassimilation of ¹⁴CO₂ generated intracellularly during oxidation of [1-¹⁴C]gluconate by the cells. It is concluded that the ratio of label captured from specifically labelled [¹⁴C]glucose is a valid and convenient measure of the relative rates of oxidation of the different positional carbon atoms within the supplied respiratory substrate. However, it is argued that failure to compensate for the incomplete absorption of ¹⁴CO₂ by an alkaline trap may distort estimates of respiration that rely on an absolute measure of the amount of ¹⁴CO₂ generated by metabolism.     

高寒矮嵩草草甸冬季CO2释放特征

冬季碳排放在高寒草地年内碳平衡中占有重要位置。为探讨高寒草地冬季碳排放特征及温度敏感性,于2003-2005年在中国科学院海北高寒草甸生态系统研究站,利用密闭箱-气相色谱法连续观测了高寒矮嵩草草甸2个冬季的生态系统、土壤呼吸通量特征。结果表明:1)高寒矮嵩草草甸冬季生态系统呼吸、土壤呼吸均具有明显的日变化和季节变化规律,温度是其主要的控制因子,能够解释44%以上的呼吸速率变异。2)冬季生态系统呼吸与土壤呼吸速率在统计上没有显著差异,土壤呼吸占生态系统呼吸的比例高达85%以上。3)2003-2004年冬季生态系统呼吸、土壤呼吸的Q₁₀值分别为1.53,1.38;2004-2005年冬季生态系统呼吸与土壤呼吸的Q₁₀值为1.86,1.68,2个冬季生态系统呼吸的Q₁₀值均高于土壤呼吸。4)未发现高寒矮嵩草草甸冷冬年份的Q₁₀值高于暖冬年份以及冬季的Q₁₀值高于生长季。