长白山阔叶红松林CO2通量与温度的关系

应用涡度相关法观测的通量数据和环境因子数据,在生态系统水平上分析了长白山阔叶红松林生长季温度与CO2通量之间的关系.结果表明：（1）在相同的光合有效辐射水平下,净生态系统CO2交换量（NEE）随温度Ta的变化趋势为,在Ta〈20℃范围内,NEE随温度的增加而增加,在Ta=20℃附近有极大值,随温度的继续增加NEE呈下降的趋势,同时NEE还具有明显的季节变化,表现为7月〉6月〉8月〉9月〉5月〉4月〉10月.（2）应用Michaelis-Menten方程计算得出最大光合速率Pmax和生态系统呼吸Re,分析其与温度的关系发现,Pmax随温度的变化呈S型曲线,Re则随着温度的升高而呈指数上升的趋势,曲线为：Re=0.0607 exp（0.0666Tα）,R^2=0.96.夜间生态系统呼吸的Q10为3.15.（3）通过对NEE与环境因子的偏相关分析表明,温度对NEE的偏相关系数在生长季呈现先减小后增大的趋势,说明在生长季初期和末期升高温度比生长季中期对NEE的影响要大.     

The acetyl-CoA pathway of autotrophic growth

Abstract The most direct conceivable route for synthesis of multicarbon compounds from CO₂ is to join two molecules of CO₂ together to make a 2-carbon compound and then polymerize the 2-carbon compound or add CO₂ successively to the 2-carbon compound to make multicarbon compounds. Recently, it has been demonstrated that the bacterium, Clostridium thermoaceticum , grows autotrophically by such a process. The mechanism involves the reduction of one molecule of CO₂ to a methyl group and then its combination with a second molecule of CO₂ and CoA to form acetyl-CoA. We have designated this autotrophic pathway the acetyl-CoA pathway [1]. Evidence is accumulating that this pathway is utilized by other bacteria that grow with CO₂ and H₂ as the source of carbon and energy. This group includes bacteria which, like C. thermoaceticum , produce acetate as a major end product and are called acetogens or acetogenic bacteria. It also includes the methane-producing bacteria and sulfate-reducing bacteria.
The purpose of this review is to examine critically the evidence that the acetyl-CoA pathway occurs in other bacteria by a mechanism that is the same or similar to that found in C. thermoaceticum . For this purpose, the mechanism of the acetyl-CoA pathway, as found in C. thermoaceticum , is described and hypothetical mechanisms for other organisms are presented based on the acetyl-CoA pathway of C. thermoaceticum . The available data have been reviewed to determine if the hypothetical schemes are in accord with presently known facts. We conclude that the formation of acetyl-CoA by other acetogens, the methanogens and sulphate-reducing bacteria occurs by a mechanism very similar to that of C. thermoaceticum .     

开放式空气二氧化碳浓度增高对小麦氮素吸收利用的影响

2001—2003年,利用我国唯一的农田开放式空气CO₂浓度增高 (free-air carbon dioxide enrichment,FACE) 技术平台,研究了FACE条件下冬小麦宁麦9号不同生育期N含量、吸收、分配和N效率的响应.结果表明：与对照相比,FACE处理使不同生育时期植株含N率显著降低,降幅达4.4%～13.4%;不同生育时期吸N量显著增加(7.4%～25.4%),生育中期的增幅明显大于生育前、后期;不同生育时期茎鞘的N积累能力相对增强,叶片N积累能力相对减弱,而对麦穗N积累能力的影响因生育进程而异;FACE处理使小麦不同生育时期N物质生产效率(5.5%～10.3%)、成熟期N收获指数(16.3%)和N籽粒生产效率(9.3%)均显著或极显著增加;增施N肥,使小麦不同生育时期N含量和吸收量呈增加趋势,使N效率呈下降趋势,而对N在各器官中分配的影响较小.     

Fruit photosynthesis

Abstract. In addition to photosynthesis as in the leaf, fruit possess a system which refixes CO₂ from the mitochondrial respiration of predominantly imported carbon. This pathway produces malate by the action of phosphoenolpyruvate carboxylase, PEPC, (E.C. 4.1.1.31) and appears to be regulated primarily by the cytosolic concentration of HCO₃/CO₂ and malate. Malate is stored in the vacuole as malic acid, constituting a major carbon pool and a potential substrate for respiration. The PEPC in apple fruit proves to be an efficient form of the enzyme with low Michaelis constants, i.e. Km = 0.09 mol m^-3 PEP and 0.2 mol m^–3 HCO₃, and large Ki= 110 mol m^-3 HCO³. In fleshy fruit, chlorophyll and chloroplasts are unevenly distributed; they resemble the C₃ sun-type and arc concentrated in the perivascular tissue, with smaller chloroplasts, fewer grana per chloroplast and a larger degree of vacuolation than commonly found in a leaf of the same species. Fruit photosynthesis often compensates for respiratory CO₂ loss in the light. However, due to respiration in the dark, CO₂ loss is in excess of photosynthetic gain in the light, such that a continual loss of CO₂ was observed in the diurnal cycle and which is maintained throughout fruit development. The rate of CO₂ exchange decreases on a fresh weight or surface basis, but increases with fruit ontogeny on a per fruit basis, causing accumulation of several percent CO₂ in the internal cavity. Stomata are present in the outer epidermis of those fruits examined, but with a 10-to 100-fold lesser frequency than in the abaxial epidermis of leaf of the same species. The number of Stomata is set at anthesis and remained constant, while the stomatal frequency decreases as the fruit surface expands. Stomata are as sensitive as in leaves in the early stages of fruit development, but often are transformed into lenticels during fruit ontogeny, thereby decreasing the permeability of the outer epidermis. The discrepancy between the CO₂-concentrating mechanism provided by PEPC analogous to C₄/CAM Photosynthesis and the kinetics of fruit PEPC, characteristic of C₃/non-autotrophic tissue, suggests the definition of a new type of ‘fruit photosynthesis’ rather than its categorization within an existing type.     

肝脏疾病微RNA胞间传递研究的现状与思考

微RNA(microRNAs)是一类通过调控基因表达参与机体生理、病理过程的非编码RNA.近来,研究证实其可在肝脏不同类型细胞间进行传递,以调控靶细胞的功能,从而参与肝脏疾病的发生发展.但其在不同类型肝脏细胞间传递的直接实验证据--细胞共培养实验仍需考虑:不同类型细胞在共培养时的数量比例及miRNAs在不同细胞间传递的方向.miRNAs的胞间传递作为肝脏疾病病理机制的重要理论创新,在研究过程中仍需要考虑临床实践.本文对近期关于微RNA胞间传递与肝脏疾病的研究进行综述,以期促进对相关研究的思考.     

我国32种鸟类DNA条形码分析

DNA条形码是一种分子分类方法,近年来在物种鉴定方面得到迅速的发展和应用.本研究分析了我国27属32种鸟类(61只)的线粒体细胞色素c氧化酶亚基Ⅰ(COⅠ)基因的条形码片段,分别用阈值法、聚类法和诊断核苷酸进行了分析,探究DNA条形码鉴定我国鸟类的准确性.结果显示,种内CO Ⅰ序列变异很小,种间存在较多的变异位点,种间的遗传距离显著大于种内的遗传距离,DNA条形码序列能够鉴定所有鸟类.     

Growing season net ecosystem CO2 exchange of two desert ecosystems with alkaline soils in Kazakhstan

Central Asia is covered by vast desert ecosystems, and the majority of these ecosystems have alkaline soils. Their contribution to global net ecosystem CO₂ exchange (NEE) is of significance simply because of their immense spatial extent. Some of the latest research reported considerable abiotic CO₂ absorption by alkaline soil, but the rate of CO₂ absorption has been questioned by peer communities. To investigate the issue of carbon cycle in Central Asian desert ecosystems with alkaline soils, we have measured the NEE using eddy covariance (EC) method at two alkaline sites during growing season in Kazakhstan. The diurnal course of mean monthly NEE followed a clear sinusoidal pattern during growing season at both sites. Both sites showed significant net carbon uptake during daytime on sunny days with high photosynthetically active radiation (PAR) but net carbon loss at nighttime and on cloudy and rainy days. NEE has strong dependency on PAR and the response of NEE to precipitation resulted in an initial and significant carbon release to the atmosphere, similar to other ecosystems. These findings indicate that biotic processes dominated the carbon processes, and the contribution of abiotic carbon process to net ecosystem CO₂ exchange may be trivial in alkaline soil desert ecosystems over Central Asia.     

森林凋落物分解重要影响因子及其研究进展

当前 ,森林凋落物分解被放在陆地生态系统碳平衡背景下进行研究 ,认识凋落物分解过程的影响因素和影响机理对理解地表碳平衡具有重要意义。凋落物在分解过程中 ,伴随有养分含量的变化 ,低品质凋落物在分解前期 (可达 2～ 3年 )会从环境中固定养分 ,特别是氮磷养分 ,而在后期则会释放出养分。凋落物本身的养分含量是影响分解速率的重要因素 ,高养分含量的凋落物分解快些 ,阔叶凋落物比针叶凋落物分解快些。有资料显示 ,在总分解率为2 9 4 %的构成中 ,理化因素、微生物因素与土壤动物因素对凋落物分解的贡献率分别为 7 2 %、8 0 %和 14 2 %。不同类型凋落物在分解过程中的土壤动物类群也不同 ,它也是造成凋落物分解速率不同的关键因素 ,通常阔叶树种凋落物分解过程中 ,会有更多的微节肢动物出现。CO2浓度升高将造成植物有机质含碳量与其它养分的比值升高 ,形成低品质的凋落物 ,从而间接影响凋落物分解速率 ,一般认为 ,全球CO2 浓度升高会加强土壤作为碳汇的功能。