Optimizing the formation of in vitro sponge primmorphs from the Chinese sponge Stylotella agminata (Ridley)

The establishment and optimization of in vitro primmorph formation from a Chinese sponge, Stylotella agminata (Ridley), collected from the South China Sea, were investigated. Our aims were to identify the key factors affecting primmorph formation in this species and to optimize the technique for developing an in vitro primmorph culture system. The size of dissociated cells from S. agminata is relatively small, in the range between 5 and 10 mum. Round-shaped primmorphs of less than 100 gm were formed 3 days after transferring the dissociated cells into seawater containing Ca2+ and Mg2+. The effect of various cell dissociation conditions, inoculum. cell density, concentration of antibiotics, pH, and temperature was further investigated upon the formation of primmorphs. The time required for primmorph formation, primmorph size distribution, and the proliferating capability were microscopically documented. Healthy sponge S. agminata, inoculum. cell density and culture temperature play a critical role for the successful formation of primmorphs and that the microbial contamination will have to be controlled. (C) 2002 Elsevier Science B.V. All rights reserved.

Soil microbial community analysis using denaturing gradient gel electrophoresis

The most biological diversity on this planet is probably harbored in soils. Understanding the diversity and function of the microbiological component of soil poses great challenges that are being overcome by the application of molecular biological approaches. This review covers one of many approaches being used: separation of polymerase chain reaction (PCR) amplicons using denaturing gradient gel electrophoresis (DGGE). Extraction of nucleic acids directly from soils allows the examination of a community without the limitation posed by cultivation. Polymerase chain reaction provides a means to increase the numbers of a target for its detection on gels. Using the rRNA genes as a target for PCR provides phylogenetic information on populations comprising communities. Fingerprints produced by this method have allowed spatial and temporal comparisons of soil communities within and between locations or among treatments. Numerous samples can be compared because of the rapid high throughput nature of this method. Scientists now have the means to begin addressing complex ecological questions about the spatial, temporal, and nutritional interactions faced by microbes in the soil environment.

Natural 13C abundance as a tracer for studies of soil organic matter dynamics

A method for measuring the long- and medium-term turnover of soil organic matter is described. Its principle is based on the variations of 13C natural isotope abundance induced by the repeated cultivations of a plant with a high 13C/12C ratio (C4 photosynthetic pathway) on a soil which has never carried any such plant. The 13C/12C ratio in soil organic matter being about equal to the 13C/12C ratio of plant materials from which it is derived, changing the 13C content of the organic inputs to the soil (by altering vegetation from C3 type into C4 type) is equivalent to a true labelling in situ of the organic matter. Two cases of continuous corn cultivation (Zea mays: δ13C = −12%.) on soils whose initial organic matter average δ13C is −26%. were studied. The quantity of organic carbon originating from corn (that is the quantity which had turned-over since the beginning of continuous cultivation) was estimated using the 13C natural abundance data. After 13 yr, 22% of total organic carbon had turned-over, in the system studied. Particle size fractions coarser than 50μm on the one hand, and finer than 2μm on the other. contained the youngest organic matters. The turnover rate of silt-sized fractions was slower

Novel uncultivated labyrinthulomycetes revealed by 18S rDNA sequences from seawater and sediment samples

Labyrinthulomycetes (Labyrinthulea) are ubiquitous marine osmoheterotrophic protists that appear to be important in decomposition of both allochthonous and autochthonous organic matter. We used a cultivation-independent method based on the labyrinthulomycete-specific primer LABY-Y to PCR amplify, clone, and sequence 68 nearly full-length 18S rDNA amplicons from 4 sediment and 3 seawater samples collected in estuarine habitats around Long Island, New York, USA. Phylogenetic analyses revealed that all 68 amplicons belonged to the Labyrinthulea. Only 15 of the 68 amplicons belonged to the thraustochytrid phylogenetic group (Thraustochytriidae). None of these 15 were similar to cultivated strains, and 11 formed a novel group. The remaining 53 amplicons belonged either to the labyrinthulid phylogenetic group (Labyrinthulidae) or to other families of Labyrinthulea. that have not yet been described. Of these amplicons, 37 were closely related to previously cultivated Aplanochytrium spp. and Oblongichytrium spp. Members of these 2 genera were also cultivated from 1 of the sediment samples. The 16 other amplicons were not closely related to cultivated strains, and 15 belonged to 5 groups of apparently novel labyrinthulomycetes. Most of the novel groups of amplicons also contained environmental sequences from surveys of protist diversity using universal 18S rDNA primers. Because the primer LABY-Y is biased against several groups of labyrinthulomycetes, particularly among the thraustochytrids, these results may underestimate the undiscovered diversity of labyrinthulomycetes.

延安日光温室蔬菜生产现状与发展对策

延安日光温室蔬菜生产从初步发展走向稳定健康发展 ,基础设施建设、栽培技术等取得了一定成绩 ,但技术力量仍感不足 ,农药、化肥污染愈加严重。提出今后进一步发展的对策

黄土高原中部丘陵区生态农业结构模式及阶段目标

分析了黄土丘陵区农业生产现状和存在的主要问题 ,指出广种薄收习惯是导致土地利用不合理 ,植被遭到破坏 ,进而水土流失加剧和生态环境恶化 ,农业生产力降低的根源。该地区生态农业建设的核心是改变广种薄收习惯 ,治理水土流失 ,不断调整优化土地利用和产业结构。依据土地资源状况提出目前阶段 1 2 34的土地利用结构模式。认为在占总土地面积 2 0 %的基本农田和果园 ,只要实行集约化经营就可实现较高的经济效益 ,70 %的土地应为林草地。根据生态农业的基本原则和当前生产水平提出生态农业建设三个阶段的不同指标和适宜治理度 ,当前该地区主导产业的发展应以资源—结构—质量型模式为主

实行三个基本转变促进黄土丘陵区农业和经济持续发展

依据黄土丘陵区几十年治理开发的正反两方面经验 ,认为该地区要真正抓住西部大开发大好机遇 ,迅速改变落后面貌 ,实现农业和经济的快速及可持续发展 ,必须在指导思想和农业生产上实现三个根本转变。即 :变以粮为主的广种薄收为高效的农林果牧综合发展 ;变自给自足的小农经济为以商品生产为主的集约经营 ;变生态经济相悖论为生态经济统一观

西部大开发中退耕还林(草)面临的挑战及其作用

根据中国西部森林的现状 ,采用生态学与地理学的方法 ,分析了因毁林开荒造成水土流失、洪涝灾害、沙尘风暴、干旱少雨、江河断流、物种减少等危害对国民经济发展所造成的影响 ,以及近几年所产生的一系列生态环境问题 .探讨了退耕还林 (草 )对我国的生态环境治理、西部持续发展、江河整治、国土整治综合措施运用、西部农民脱贫致富的作用 .

玉米地膜覆盖的土壤环境效应

通过田间试验研究了地膜覆盖和露地栽培对玉米的土壤温度、水分、养分、盐分含量和土壤生物学特性及硝酸盐含量的变化。结果表明,在玉米生长前期,地膜覆盖5,10,15,20,25 cm土层的土壤日平均温度比露地提高2.4℃、3.0℃、2.9℃、2.2℃、2.7℃,6~7月份比露地降低1.1℃、0.5℃、0.5℃、0.6℃、0.6℃。地膜覆盖0~10,10~20,20~30,30~40 cm土层的土壤含水量分别比露地增加18.84%、10.67%、11.12%和8.9%。地膜覆盖增强了土壤蔗糖酶和碱性磷酸酶的活性,增加了土壤微生物的数量、CO2浓度、土壤呼吸和土壤NO3--N的含量,减少了土壤氮素的损失。地膜覆盖降低了土壤有机质、氮素、速效磷的含量、过氧化氢酶和脲酶的活性及土壤表层的盐分含量。地膜覆盖提高了玉米的生物量和经济产量。

挖掘作物抗旱节水潜力——作物对多变低水环境的适应与调节

本文针对半干旱地区多变低水的实际田间环境,讨论了作物对不同干旱类型的反应,适度干旱后复水的生理补偿效应,不同类型作物在干湿交替条件下的差异,以及增强作物对多变水环境适应的技术.同时,就多变低水环境的概念、作物对多变低水环境的适应机理以及作物抗旱生理研究与旱农生产实际相衔接等问题提出了若干看法.

抢救“土壤水库”实为黄土高原生态环境综合治理与可持续发展的关键——四论黄土高原国土整治28字方略

现在全国上下深切关注着黄河的重大问题及其对策。其实问题的根源都出自人们对黄河流域尤其黄土高原自然资源的掠夺式开发 ,形成了“3个恶性循环”:广种薄收 ,薄收更广种 ,虽是罪魁祸首 ,但常反被忽视 ,致使生态环境脆弱 ,人民长期贫困 ;只有下游河床越淤越高 ,防洪大堤越筑越高 ,越高越险和断流历时越来越长 ,上溯速度越来越快 2个恶性循环的危害才使人惊恐。不难看出 ,这是恰与形成黄土高原自然规律完全相悖的人为地质过程的结果。可惜它还未引起人们深入充分的认识 ,难怪一向短缺一个为各家合力共识的治本对策。当今国家将经济发展的重点向中、西部转移 ,并要求重建一个山川秀美的大西北 ,黄土高原的持续开发与治理对策就显得更为举足轻重。由此其各项对策都将面临着转变观念、调整思路、实事求是地进行科学分析和抉择。笔者最近从陆地生态的发生发展及其整个地质历史演变过程的研究中发现 :“土壤水库”的发生发展及其演变是陆地生态发生发展的关键和“动力”,只要维护土壤水库的正常发展就能更好地保卫生态环境。黄土高原地区由于得天独厚的降尘堆积环境条件和持续的成壤过程 ,可使降水具有直接渗入“地下水库”的特殊功能。只要维护住高入渗土壤水库的存在就...

陕北丘陵沟壑区坡地不同耕作法综合效益研究

以在陕北丘陵沟壑区坡耕地不同耕作法试验 7a的资料为依据 ,论述了不同耕作法的水分利用、土壤水分平衡及单位面积产量和水土保持等综合效益。作物生长主要依赖生育期内自然降雨 ;作物耗水量与每年生育期降雨量及土壤供水量呈显著正相关 ,不同耕作法之间变化不大 ,作物主要利用 0— 12 0 cm土层内的水分。同一年内不同耕作法的综合效益从优到劣、由高到低的排列顺序为宽梯田 >窄梯田 >水平沟 >平播 >水平阶 >隔坡梯田。而水土保持效益排列顺序为 :梯田 >水平沟 >隔坡梯田 >水平阶 >平播 >裸地。认为坡耕地确实应尽快退耕还林还草 ,以加速陕北生态环境建设 ,推进农业结构的战略性调整。

渭北旱塬持续高效农田种植模式研究与示范

根据渭北旱塬自然经济特点 ,提出了该区农业持续发展的关键技术和增产新途径——农田高效优化种植模式 (以双元覆盖小麦为主 )。通过 4a的试验示范与推广 ,结果表明 :该模式可较对照增产小麦6 2 .92 % ;复种黄豆增收 1 5 0 0～ 2 2 5 0 kg/ hm2 ,较对照增产 1 0 0 %。该模式的聚水、保墒、增温和促进有机质矿化、增加土壤养分效应显著 ,可使土壤水、热环境改善 ,充分利用水资源 ,提高用水效率。

陕北丘陵沟壑区苹果优质丰产栽培体系研究

园址选择、优良品种搭配、坡地改良、合理施肥与抗旱栽培、合理修剪等是陕北丘陵沟壑区苹果优质丰产的保障 ,且同时论述了各项措施的操作依据和方法

不同保墒耕作方法在旱地上的保墒效果及增产效应

采用田间试验研究了留茬少耕秸秆全程覆盖、免耕补充灌溉和传统保墒耕作 3种方法对旱地土壤水分及小麦产量的影响。结果表明 ,留茬少耕秸秆覆盖增加了夏闲期农田的蓄水量 ,为旱地小麦播种出苗提供了水分保证。小麦收获时的土壤水分含量 ,0～ 60 cm的土壤有效蓄水量传统保墒方法为 6.4mm,免耕补充灌水的为 6.7mm,留茬少耕秸秆全程覆盖方法为 1 5 .3 mm,留茬少耕秸秆全程覆盖方法的蓄水量多 ;60～ 1 0 0 cm的土壤有效蓄水量传统保墒方法为 3 0 .9mm,免耕补充灌水为 2 0 .3 mm,留茬少耕秸秆全程覆盖方法为 3 3 .5 mm,也是留茬少耕秸秆全程覆盖方法的蓄水量多。留茬少耕秸秆全程覆盖比传统耕作保墒技术增产 6.7%～ 5 4.8%。留茬少耕秸秆覆盖技术 ,提高了小麦播种时的底墒、灌浆时的土壤水含量 ,是一种有效的蓄水保墒、提高旱地小麦产量的方法