Microchambers and video-enhanced light microscopy for monitoring cellular events in living hyphae of arbuscular mycorrhizal fungi

Mycelial elongation and protoplasmic flow rate in vitro were monitored for germinated spores of Gigaspora rosea and Glomus caledonium respectively, growing on membranes in microchambers, by using a combination of time-lapse and video-enhanced light microscopy and image analysis. The microchambers allowed continuous observation of living mycelium over a period of several hours during which protoplasm flow and bidirectional movements of cellular organelles and particles were monitored in individual hyphae. Growth rate of G. rosea hyphae, calculated 8 days after germination, was 2.64 μm/min. Protoplasmic flow rate, measured on the basis of the movement of particles, ranged from 2.98 to 4.27 μm/s in living hyphae of G. caledonium. We showed that G. rosea, when growing in axenic culture in the absence of the host, ceased growth within 8 days of germination and underwent a process of protoplasm retraction from hyphal tips, leading to the formation of empty mycelial segments. A process of resource reallocation was inferred in spores of G. rosea showing multiple germination. Detailed developmental studies of living hyphae by using microchambers could provide useful information on spatio-temporal dimensions of cellular events occurring in arbuscular mycorrhizal fungi. This revised version was published online in June 2006 with corrections to the Cover Date.     

Inoculation with arbuscular mycorrhizal fungi: the status quo in Japan and the future prospects

Inoculation of arbuscular mycorrhizal (AM) fungi has potential benefits in not only sustainable crop production but also environmental conservation. However, the difficulty of inoculum production due to the obligate biotrophic nature of AM fungi has been the biggest obstacle to putting inoculation into practice. Nevertheless, several companies have sought to produce inoculum of AM fungi. Firstly in this review, the present status of inoculum production and its use in Japan is described. Secondly, although the effectiveness of inoculation is primarily limited by environmental and biological factors, some possible ways to improve inoculation performance are discussed. Approaches include use of chemicals to increase spore germination and colonization and soil application of charcoal to provide a microhabitat for AM fungi to colonize and survive.     

丛枝菌根真菌和植物寄生线虫

本文综述了土壤微生物中丛枝菌根真菌和植物寄生线虫的互作关系及其互作机理,并阐述了丛枝菌根真菌在防治植物线虫病害方面的应用前景和实际操作中应注意的技术环节。     

梅根际丛枝菌根真菌五个中国新记录种

5种丛枝菌根真菌微刺球囊霉Glomus spinuliferum、大型无梗囊霉Acaulospora colossica、单氏内生囊霉Intraspora schenckii、巴西类球囊霉Paraglomus brasilianum和双疣盾巨孢囊霉Scutellospora dipapillosa是从梅Prunus mumeSieb.etZucc.的根围土壤中分离的中国新记录种。本文对他们的形态特征进行重新描述和图解。这5个种的标本贮藏在中国科学院微生物研究所菌物标本馆(HMAS)中。     

Screening of arbuscular mycorrhizal fungi for the revegetation of eroded red soils in subtropical China

Some acidic red soils in hilly regions of subtropical China were degraded as a result of slope erosion following the removal of natural vegetation, primarily for fuel. Revegetation is important for the recovery of the degraded ecosystem, but plant growth is limited by the low fertility of eroded sites. One factor contributing to the low fertility may be low inoculum density of arbuscular mycorrhizal (AM) fungi. Compared to red soils under natural vegetation or in agricultural production, substrates on eroded sites had significantly lower AM fungal propagule densities. Thus, the management and/or application of AM fungi may increase plant growth and accelerate revegetation. Thirteen species of AM fungi were identified in red soils by spore morphology. Scutellospora heterogama, Glomus manihotis, Gigaspora margarita, Glomus aggregatum and Acaulospora laevis were among the most common according to spore numbers. Pot cultures were used to isolate and propagate 14 isolates of AM fungi indigenous to red soil. The effectiveness of each fungus in promotion of growth of mungbean was evaluated in red soil. For comparison, three isolates from northern China, known to be highly effective in neutral soils, and two isolates from Australia, known to be from acidic soil were used. Effectiveness was positively related to root infection (r ² = 0.601). For two of these isolates, Glomus caledonium (isolated from northern China) and Glomus manihotis (an isolate indigenous to red soil), the applied P concentration giving the highest infection and response to infection was approximately 17.5 mg P kg^–1 soil. In field experiments in which this concentration of P was applied, the five most effective isolates were tested on mungbean. The Glomus caledonium isolate from northern China was the most effective, followed by the indigenous Glomus manihotis isolate. The Glomus caledonium isolate was also shown to be effective on Lespedeza formosa, which is commonly used in revegetation efforts. We conclude that inoculation of plants with selected isolates of AM fungi may aid in revegetation efforts on eroded red soils in subtropical China.     

丛枝菌根真菌在土壤氮素循环中的作用

作为植物需求量最大的营养元素,氮素是陆地生态系统初级生产力的主要限制因子。丛枝菌根真菌能与地球上80%以上的陆生植物形成菌根共生体,帮助宿主植物吸收土壤中的P、N等矿质养分。目前,丛枝菌根真菌与氮素循环相关研究侧重于真菌对氮素的吸收形态以及共生体中氮的传输代谢机制,却忽略了丛枝菌根真菌在固氮过程、矿化与吸收过程、硝化过程、反硝化过程以及氮素淋洗过程等土壤氮素循环过程中所起到的潜在作用,并且越来越多的证据也表明丛枝菌根真菌是影响土壤氮素循环过程的重要因子。总结了丛枝菌根真菌可利用的氮素形态及真菌的氮代谢转运相关基因的研究现状;重点分析了丛枝菌根真菌在调控土壤氮素循环过程中的潜在作用以及在生态系统中的重要生态学意义,同时提出了丛枝菌根真菌在土壤氮素循环过程中一些需要深入研究的问题。     

内蒙古草原常见植物根围AM真菌

调查了内蒙古草原地区常见植物根围丛枝菌根(AM)真菌的资源状况。共分离鉴定出Acaulospora属2种,Glomus属19种,Scutellospora属1种;其中布氏球囊霉Glomus brohultii是我国新记录种。     

喀斯特植被演替过程土壤丛枝菌根真菌(AMF)多样性

喀斯特生态系统维持了丰富的微生物多样性,丛枝菌根真菌(Arbuscular mycorrhizal fungi,AMF)结构和组成会随喀斯特植被演替而改变。以贵州贵阳花溪、毕节织金和关岭花江典型喀斯特区域按时空替代法采集了乔木林、灌木林和草本群落样地土壤,采用Illumina HiSeq分子测序技术,通过OTU聚类分析、物种注释及数据库比对,探索了喀斯特不同演替阶段土壤AMF物种多样性。结果表明:(1)喀斯特生境土壤获得球囊菌门Glomeromycota OTU为275个,分属于4目8科13属19种,属水平上AMF丰度表明根内根孢囊霉属Rhizophagus为优势属,花江拥有最高AMF丰富度,缩隔球囊霉Septoglomus constrictum、根内根孢囊霉Rhizophagus intraradices、Claroideoglomus sp. MIB8381和稀有内养囊霉Entrophospora infrequens均分布于各样地的不同植被演替阶段,为常见种。(2)AM真菌多样性Shannon指数与Simpson指数在不同演替阶段表现为花溪:乔木≈灌木草本(P0.05)、花江:灌木≈草本乔木(P0.05)、织金:乔木灌木草本,但差异不显著,Chao1和Abundance-based coverag estimator(ACE)指数表现为花江灌木≈草地乔木(P0.05)。(3)Spearman相关性分析表明土壤全磷与AMF ACE指数显著负相关,且与Chao1指数极显著负相关;速效磷与Shannon和Simpson指数显著负相关。(4)典范对应分析(Canonical Correlation Analysis,CCA)表明土壤全氮、速效氮、有机质、全磷和速效钾与AMF群落分布有显著相关性。结果表明喀斯特植被演替过程中土壤丛枝菌根真菌多样性随着演替进行或升高或降低,无一致变化规律,并与土壤理化性质关系密切,其中以磷的影响最大。