黑石顶森林中次生裸地上的群落演替进程研究

黑石顶人工林演变成的次生针阔混交林于1986年皆伐火烧成裸地,其恢复进程表明：次生裸地上群落恢复迅速,从由马尾松（Plnusm。）一木荷（Schimasuperba）一杉木（Cunninghamialanceolata）为主的针阔混交林开始,至1990年,森林群落已基本重建起来,其中乔木种类达42种,与样地原群落的相似系数为0．6250,物种多样性指数和均匀度指数略高于样地原群落。与1986年定位的其他样地上的群落按林龄由小到大视作一大于50年的演替系列进行比较,发现从裸地到针阀混交林,再到阔叶林的演替过程中,乔木种总数和个体密度趋于增加,物种多样性先迅速增加,然后呈现下降趋势,再缓慢增加。     

小良试验站三种地表径流效应的对比研究

基于连续１０年的观测,本文对比研究了３种植被类型的地表径流效应,证明了混交林的水文效益无论从哪方面较桉树林和裸地明显,并且随着年度的推移。混交林的水文效益更加突出,发生产流的最小降雨量条件为：混交林３０．２ｍｍ,桉树林５．１ｍｍ,裸地６．０ｍｍ,产流发生时饱和土层厚度分别为１２．６ｍｍ,３．４ｍｍ,６．３ｍｍ。理论上,作者阐明了３种植被类型下的产流类型提出了桉树林下地表更易形成击实层这样一个设想,     

Excess free energies of interaction of chlorophyll a with monogalactosyldiacylglycerol and phytol a mixed monolayer study

The surface pressure isotherms of chlorophyll a, monogalactosyldiacylglycerol and phytol at the air-water interface were studied on a Langmuir trough at 20.0±0.5°C. The subphase was a phosphate buffer, 10^?3 M at pH 8.0. The extrapolated limiting areas per molecule are 115, 82 and 38 Ų/molecule, respectively. The isotherms of eight mixtures of chlorophyll a with monogalactosyldiacylglycerol and eight mixtures of chlorophyll a with phytol, covering in both cases the whole range of molar fractions have also been measured. The results for the mixed monolayers were analysed in terms of the additivity rule. They show that a small negative deviation with respect to ideality is observed upon mixing chlorophyll a with monogalactosyldiacylglycerol. However, chlorophyll a forms an ideal two-dimensional solution when mixed with phytol. The excess free energies of mixing of chlorophyll a with monogalactosyldiacylglycerol as a function of concentration were calculated from the surface pressure isotherms at 10, 15, 20 and 25 mN·m^?1. The values are negative, reflecting the interaction prevailing between these components in the monolayers. For the four surface pressures studied, the excess free energies are symmetrical with respect to the mode fraction. The values for an equimolar mixture range from ?300 to ?540 J·mol^?1 at 10 and 25 mN·m^?1, respectively. A comparison between the thermodynamics of mixing of chlorophyll a with monogalactosyldiacylglycerol and phytol suggests that the polar head of monogalactosyldiacylglycerol together with the polar groups of chlorophyll a are probably involved in the interaction. However, this does not completely rule out the possibility that structural effects due to a different packing of chlorophyll a with monogalactosyldiacylglycerol and phytol may also be involved. Furthermore it is shown that the small interactions between these constituents are not inconsistent with the specific coupling existing between the apoprotein of the chlorophyll a-protein complexes and chlorophyll a.     

早期分解中油松与阔叶树种凋落叶混合分解效应及其相互影响

以油松（Pinus tabuliformis Carrière）和5种阔叶树的凋落叶为对象,使用分解袋法在室内进行为期6个月的针阔混合分解实验,研究产生的混合分解效应、针阔凋落叶对彼此分解速率的影响及其可能产生机理。结果显示：（1）油松分别与红桦（Betula albo-sinensis Burk.）、灰楸（Catalpa fargesii Bur.）、太白杨（Populus purdomii Rehd.）凋落叶混合对分解速率均产生加性效应,但其中油松凋落叶分解受到显著促进,而阔叶凋落叶分解受到显著抑制。油松与杜仲（Eucommia ulmoides Oliver）凋落叶混合时两者分解速率均显著降低,油松与槭树（Acer tsinglingense Fang et Hsieh）凋落叶混合时两者分解速率均显著提高;（2）总体而言,在蔗糖酶、羧甲基纤维素酶和多酚氧化酶参与凋落叶分解的主要时期,红桦、灰楸、太白杨分别与油松凋落叶混合分解使土壤中这3种酶的活性较油松单独分解时显著提高,而较阔叶凋落叶单独分解时显著降低;油松与杜仲混合分解使这3种酶活性较两者单独分解时显著降低,而油松与槭树混合分解则产生相反效果。本研究结果表明,从凋落叶混合分解对物质循环影响的角度考虑,红桦、灰楸、太白杨和槭树可以用于油松纯林的混交改造,但应注意混交对阔叶树种分解的抑制;杜仲与油松凋落叶混合分解将会妨碍彼此养分循环,不宜混交改造。     

Regulatory flexibility of methylotrophic yeasts in chemostat cultures: Simultaneous assimilation of glucose and methanol at a fixed dilution rate

The influence of the composition of methanol/glucose-mixtures as only sources of carbon and energy on growth and regulation of the synthesis of enzymes involved in methanol-dissimilation was studied under chemostat conditions at a fixed dilution rate with the methylotrophic yeasts Hansenula polymorpha and Kloeckera sp. 2201. Both carbon sources were found to be utilized completely independently of the composition of the C₁/C₆ mixture. Using mixtures of ¹⁴C-labelled methanol and glucose the growth yield for glucose was found to be constant for all C₁/C₆-mixtures tested and both yeasts. The growth yield for methanol, however, was reduced by up to 25% when the proportion of methanol in the inflowing medium was lower than 20% (w/w with respect to glucose) for H. polymorpha and 50% (w/w with respect to glucose) for Kloeckera sp. 2201 respectively. During growth with C₁/C₆-mixtures containing higher C₁-proportions of methanol regular growth yields for methanol were recorded which corresponded to the growth yields found with methanol as the only carbon source.The regulation of the synthesis of the enzymes of the dissimilatory pathway for methanol was found to be under multiple control. Although glucose was present in the medium methanol had a positive effect on the synthesis of these enzymes. Thus, in addition to derepression induction by methanol was also observed. This inductive effect was found to increase with increasing proportions of methanol in the mixture. Depending on the enzyme, 10–40% methanol in the mixture resulted in a maximal induction with enzyme specific activities equal to those found in cells grown with methanol as the only carbon source. No further enhancements in enzyme specific activities were observed during growth on mixtures containing more than 40% methanol.Abbreviations and terms C₁ Methanol - C₆ glucose - C₁/C₆ mixture compositions are given in % (w/w) - C₀ concentration of ¹⁴C in the inflowing medium (DPM ml^-1) - C(t) concentration of ¹⁴C incorporated in cells as a function of time t (DPM ml^-1) - d dilution rate (h^-1) - DPM disintegrations per minute - q _s q _C1 and q _C6 are specific rates of consumption of substrate, methanol and glucose respectively [g (g cell dry weight)^-1 h^-1] - q _O2 and q _CO2 are the specific rates of oxygen consumption and carbon dioxide release [mmol (g cell dry weight)^-1 h^-1] - RQ respiration quotient (q _CO2 q _O2 ^-1) - s _C1 and s _C6 are the residual concentrations of methanol and glucose in the culture liquid (g l^-1) - s _O/C1 and s _O/C6 are the concentrations of methanol and glucose in the inflowing medium (g l^-1) - Sp.A. enzyme specific activity - x cell dry weight concentration (g l^-1) - Y _X/C1 and Y _X/C6 are growth yields on methanol and glucose respectively (g cell dry weight (g substrate)^-1 - Y _C/C1 growth yield with methanol with respect to carbon (g carbon assimilated (g carbon supplied)^-1 - _m maximum specific growth rate (h^-1)     

Soil temperature and nitrogen effects on response of flooded and nonflooded rice to zinc

Summary Response of direct seeded rice (cv. Bluebelle) to Zn was studied in flooded and nonflooded (field capacity) Crowley soil (pH 7.6) maintained at soil temperatures of 18 and 30°C. Urea and (NH₄)₂SO₄ were compared as sources of N to determine their effect on plant uptake of Zn from ZnSO₄ either mixed or surface applied to the soil. Grain yields were slightly higher from nonflooded than from flooded soil. Higher dry matter production at 30 than at 18°C was not related to Zn nutrition. Urea and (NH₄)₂SO₄ resulted in similar yields and Zn uptake by flooded rice, but (NH₄)₂SO₄ was superior for nonflooded rice in the absence of applied Zn. More fixation of mixed Zn by the limed Crowley soil probably caused its lower effectiveness, as compared to surface-applied Zn.     

Flore mixte au permien supérieur en arabie saoudite

The study of some silicified woods and prints collectedin a Permian locality of the central part of Saudi Arabia leads us to identify the following genus and species: Dadoxylon sp. 1, Dadoxylon sp. 2, Cordaites sp., Annularia mucronataSchenk, Lobatannularia cf. heianensisKodaira, Pecopteris phegopteroidesO. Feistmantel, Pecopteris cf. wongiiHalle, Neuropteridium schyfsmae n. sp., Fascipteris hallei (Kawasaki) Lee & alii, Cladophlebis aff. royleiArber, Taeniopteris sp., (?) Marattiopsis sp. and Zamiopteris sp. This is a flora very similar to the Upper Permian flora from Hazro (Turkey) described in 1962 by R.H. Wagner, which has the particularity to have some cathaysian type elements, the presence of which engages us to consider the eventuality of a relationship between Eurameria and Cathaysia during Permian and the existence of a geographical extension area for cathaysian elements whose orientation was approximately the axe of the actual Mediterranean sea, probably on the south and along the Tethys (?) (the geographical position of the Cathaysia during Permian is indeterminate).     

Regulation of autotrophic and heterotrophic metabolism in Pseudomonas oxalaticus OX1: Growth on mixtures of acetate and formate in continuous culture

Growth of Pseudomonas oxalaticus in carbon- and energy-limited continuous cultures with mixtures of acetate and formate resulted in the simultaneous utilization of both substrates at all dilution rates tested. During growth on these mixtures, acetate repressed the synthesis of ribulosebisphosphate carboxylase. The degree of this repression was dependent on the dilution rate and on the ratio of acetate and formate in the medium reservoir. At fixed acetate and formate concentrations in the inflowing medium of 30 and 100 mM, respectively, and dilution rates above 0.10h^-1, the severe repression of autotrophic enzymes resulted in a marked increase in bacterial dry weight compared to the growth yield of the organisms on the two substrates separately. Also, at these dilution rates a significant increase in isocitrate lyase activity was observed in the cells as compared to growth on acetate alone. This indicated that under these conditions more acetate was assimilated and less dissimilated since acetate was partly replaced by formate as the energy source. When formate was added to the reservoir of an acetate-limited culture (S_R=30 mM), derepression of RuBPCase synthesis was observed at formate concentrations of 50 mM and above. Below this concentration formate only served as an energy source for acetate assimilation; when its concentration was increased above 50 mM a progressively increasing contribution of carbon dioxide fixation to the total carbon assimilation was observed as the activity of RuBPCase in the cells increased. It is concluded that in Pseudomonas oxalaticus the synthesis of enzymes involved in autotrophic carbon dioxide fixation via the Calvin cycle is regulated by a repression/derepression mechanism.Abbreviations RuBPCase ribulosebisphosphate carboxylase - PMS phenazine methosulphate - DCPIP 2,6-dichlorophenol-indophenol - FDH formate dehydrogenase - S_R concentration of growth-limiting substrate in reservoir