不同光照条件对白车轴草根际微生物的影响

以白车轴草根际和根外土样为试村,研究了不同光照条件对白车轴草根际微生物的影响。结果表明:根际、根外细菌、放线菌、氨化细菌、好氧性纤维素分解菌、硝化细菌的数量及根际效应均随光照增加而提高;真菌、反硝化细的数量及根际效应均随光照减少而上升;不同光照条件下,各类微生物的根际效应明显。     

嫁接对东北山樱（Cerasus sachalinensis Kom.）根际微生物群落结构及多样性的影响

在植物根际生态系统中,土壤微生物的作用不可忽视,栽培措施的改变会影响根际微生物群落结构,进而影响植物生长。野生条件下,东北山樱嫁接后几十年表现良好,与栽培条件下差异显著。为此,研究野生条件下嫁接对东北山樱根际微生物群落结构以及多样性的影响,对改善樱桃栽培环境及可持续发展具有重要意义。笔者利用选择性培养基,研究野生条件下嫁接与砧木东北山樱根际细菌、真菌、放线菌的数量、群落组成以及种群多样性。结果表明,嫁接对东北山樱根际微生物数量、群落结构及多样性影响差异显著。嫁接显著增加东北山樱根际微生物数量,并形成了以细菌芽孢杆菌属、固氮菌属;真菌木霉菌属、毛霉菌属;放线菌（链霉菌属）吸水类群、烬灰类群和青色类群为主的优势菌属;发现特有细菌埃希氏菌属、节杆菌属、不动杆菌属、德克斯氏菌属、葡萄球菌属。     

三唑酮对西瓜根际木霉菌与尖孢镰刀菌竞争定殖的影响

 在尖孢镰刀菌厚垣孢子土中,接种1×10⁶cfu/g土的木霉菌孢子,并加入4~12μg/g土三唑酮。木霉菌加各三唑酮处理的尖孢镰刀菌厚垣孢子在西瓜根际的萌发率低于不加药的木霉菌对照,并与三唑酮剂量成反比;尖孢镰刀菌的根际竞争指数,以及在绝大部分根段根际的种群密度也低于不加药的木霉菌对照;而在上述条件下木霉菌的根际竞争指数以及在某些根段根际的种群密度十分接近或超过不加药的木霉菌对照。本文还讨论了不同木霉菌量和不同尖孢镰刀菌量条件下,三唑酮剂量对木霉菌和病原尖孢镰刀菌在西瓜根际竞争定殖的影响。     

百合生育期根际土壤微生物和酶活性的变化

 在自然生长条件下,研究了不同品种百合在不同生育期根际土壤微生物种类、数量和土壤酶（过氧化氢酶、脲酶、碱性磷酸酶）活性的变化规律。结果表明：在百合生育期内,土壤微生物以细菌最多,对百合的根际效应也最敏感;其次为真菌,再次为放线菌。不同生育阶段以显蕾期根际土壤细菌和放线菌的数量最多,但显蕾期以后二者根际效应方向相反;根际土壤真菌的数量和根际效应在鳞茎充实期均达到最大。土壤脲酶活性和碱性磷酸酶活性在百合生育期内表现为先降、后升、再降的趋势,即在显蕾期形成峰值,根际效应显著,随生殖生长的推进其活性及根际效应均逐渐减弱;而过氧化氢酶活性则先上升后下降,根际效应不明显。在百合—土壤—微生物相互作用的体系中,根际土壤微生物的种类、数量和酶活性明显受到百合生长发育的影响。     

Experimental platforms for the investigation of spatiotemporal patterns in the rhizosphere—Laboratory and field scale

The numerous feedback loops between roots, microorganisms, soil chemical and physical properties, and environmental variables result in spatial parameter patterns which are highly dynamic in time. In order to improve our understanding of the related rhizosphere processes and their relevance at the soil–plant system scale, experimental platforms are required. Those platforms should enable (1) to relate small scale observations (nm to dm) to system behaviour, (2) the integration of physical, chemical and biological sampling approaches within the same experiment, and (3) sampling at different time points during the life cycle of the system in question. Here we describe what requirements have to be met and to what extent this has been achieved in practice by the experimental platforms which were set up within the framework of DFG priority programme 2089 “Rhizosphere Spatiotemporal Organisation—a key to rhizosphere functions”. It is discussed to what extent theoretical considerations could be accommodated, in particular for the comparison across scales, i.e., from laboratory to field scale. The latter scale is of utmost importance to overcome the trade‐off between fraction of life cycle covered and the avoidance of unrealistic root length densities.     

根肿病生防菌Zhihengliuella aestuarii B18定殖能力及防效分析

Zhihengliuella aestuarii B18是一株对十字花科根肿病菌Plasmodiophora brassicae具有抑制作用的优良生防菌株。为探明其生防潜能,本文通过抗生素抗性标记法、盆栽试验和田间小区试验研究了B18在不同土壤pH、土壤温度、土壤含水量、初始接种浓度、蔬菜作物以及不同土壤类型中的定殖动态。灭菌土试验结果表明:调节土壤pH 7.5～8.5,含水量10%～30%,放置于10～25℃,70 d后B18定殖菌量保持在105～107 cfu/g。盆栽试验结果表明:初始接种菌液浓度为109 cfu/mL时,45 d后根际土中定殖菌量可稳定在104～105cfu/g。将50 mL浓度为2×109 cfu/mL的生防菌菌液接种于田间不同类型土壤后,第30天定殖菌量分别为病田8.7×105cfu/g,病土1.02×105cfu/g,健田8.5×104cfu/g,健土2.6×104cfu/g,即定殖能力由强到弱依次为:病田＞病土＞健田＞健土。且病田中B18在根际土中可存活至45 d且菌量保持在104 cfu/g,根内可存活至31 d且菌量保持在104 cfu/g。田间调查结果显示B18在病田和病土中对榨菜根肿病的防效分别为42.01%和47.53%,增产率分别为37.24%和40.22%。     

Microbial diversity and multidimensional interactions in the rice ecosystem

The sustainability of rice production systems globally is intricately related to the chemistry, physics and biology of rice soils – with basic properties differing considerably in wet/dry land soils, tropical/temperate areas or even with the soil surface or rhizosphere niche of the field. Rice fields represent unique aqua-terrestrial ecosystems in which the tremendous diversity of soil microbes, soil fauna and plants – ranging in function from nitrogen fixers, nitrifiers, methanogens, methane oxidizers, phosphate-dissolving microbes, sulfur oxidizers to catabolizers of pesticides is observed. This diversity is inclusive of bacteria, cyanobacteria, archaea, planctomycetes and β-proteobacteria, besides the increasing members of endophytes associated. The complexity and dynamic nature of this ecosystem requires in-depth investigations of the tripartite interactions among plants, microbes and the soil–water environment. This needs to be complemented with studies on the ecological compartmentalization due to diffusion gradients of nutrients and gases, which is of extreme significance in the current scenario of problems associated with greenhouse gas emissions from agricultural areas, especially rice paddies. This article provides an overview of the interactions between the microflora and crop, with emphasis on nutrient transformations in the rhizosphere, so as to develop effective and efficient environmentally sustainable strategies for this crop.     

Tomato seedling development is improved by a substrate inoculated with a combination of rhizobacteria and fungi

Chile's seedling production industry has been growing for the last 10 years, and demand has actually reached 1250 million seedlings per year. This system has special relevance due to the high cost of seeds. In addition, there is an increasing demand for substituting synthetic agrochemicals. Therefore, the potential use of plant growth-promoting rhizobacteria (PGPR) in tomato production has been investigated. Before sowing, the micro-organisms provided by Biogram S.A. were inoculated into the substrate diluted in 250 mL/L unchlorinated water. The experiment was laid out in a ‘split-plot’ design with the two plant substrates as main plots and the inoculants as subplots, including six replicates per treatment. Tomato seedlings were grown using two different plant substrates: a mixture of 70% peat and 30% perlite by volume, and a substrate with 20% peat, 20% perlite and 60% compost by volume, both inoculated with Bacillus subtilis or Pseudomonas fluorescens or Bioroot®, which is a commercial product containing B. subtilis, P. fluorescens, Trichoderma harzianum, yeast, algae and Nocardia. For control, uninoculated tomato seedlings were grown on the respective plant substrates. Variance analysis did not identify significant interactions between substrate type (main plots) and inoculation treatment (subplots), P ≤ 0.05. There were significant differences between inoculants (P ≤ 0.05). Means were compared by using the Tukey's multiple range test. Tomato growth in terms of leaf area (cm²/plant) and shoot and root dry weight (g/10 plants) was improved for the seedlings grown on the substrate with 70% peat and 30% perlite, compared to the compost containing an alternative that is valid for both uninoculated perlite peat and all inoculated treatments where perlite peat was outstanding. Inoculation with Bioroot® improved the leaf area, shoot dry weight, root dry weight, radical contact area, volume of roots and root forks compared with the control without inoculation, when both plant substrates were analysed together. Thus, inoculation with Bioroot® can be recommended as an alternative to tomato seedling growers' dependence on synthetic agrochemicals.     

灌后通气处理对温室黄瓜生长和品质的影响

Rhizosphere aeration, irrigation with aerated water, and post-irrigation aeration would positively impact crop growth and yield. The objective of this study was to determine the effect of 4 post-irrigation aeration levels on plant growth, yield, irrigation-use efficiency （IUE）, and fruit market and nutritional quality of greenhouse cucumber under subsurface drip irrigation （SDI） and furrow irrigation （FI）. The post-irrigation aeration levels were 0.00, 0.50, 0.75, and 1.00 times half the estimated porosity of the plot rhizosphere. The experimental design was a two-faetor split-plot in randomized complete blocks with irrigation （FI and SDI） as the main treatments and 4 aeration levels as the sub-treatments. Ridge and furrow main plots （2.4 m ~ 2.4 m） with 4 ridges were replicated 5 times. Each of the 4 ridges （1.44 m2 in area） in the main plots was used as a sub-treatment plot. The results showed that post-irrigation aeration enhanced greenhouse cucumber plant growth, yield, IUE, and fruit market and nutritional quality. These parameters generally increased with increasing aeration levels under both FI and SDI. The aeration effect was generally higher under SDI than FI, and the IUE under SDI was almost twice that under FI. Further investigation would be required to elucidate the plant physiological mechanisms and soil processes responsible for the observed effects.     

Community structure of microeukaryotes in a rice rhizosphere revealed by DNA-based PCR-DGGE

Rice roots provide a specific habitat for microorganisms in the rhizosphere of a submerged field through supply of oxygen and organic matter. Many studies have focused on the microbial community in the rice rhizosphere, but less is still known about the microeukaryotic community structure of rice rhizosphere. This study explored the microeukaryotic community structure of a rice rhizosphere through denaturing gradient gel electrophoresis (DGGE) targeting 18S rRNA gene. The rice roots and the rhizosphere soil samples, which were collected from a field under rice-wheat rotation system, were separately analyzed. To characterize the rice rhizosphere-specific community, the bulk soil of rice field and the wheat rhizosphere samples were also examined. DGGE fingerprints showed that the microeukaryotic community of rice roots were distinct from the community of the bulk soil and showed a temporal shift with the growth stage. The rhizosphere soil community was distinct from the root and bulk soil communities, but this could be explained by that the root and bulk soil communities were shared in the rhizosphere. The rice rhizosphere community was also distinct from those in the wheat rhizosphere. Microeukaryotes that characterized the rice rhizosphere (roots and the rhizosphere soil) community could be affiliated to Polymyxa, flagellates, and oomycetes, which suggested that microeukaryotes with various ecological roles, e.g., parasites, bacterial grazers, and decomposers, inhabit the rice rhizosphere. The results showed that the rice root and its growth stages are key factors shaping the microeukaryotic community structure in the rhizosphere.