Effects of species of VA-mycorrhizal fungi on growth and mineral uptake of sorghum at different temperatures

Sorghum [Sorghum bicolor (L.) Moench] plants were grown in growth chambers at 20, 25 and 30°C in a low P Typic Argiudoll (3.65 µg P g^–1 soil, pH 8.3) inoculated with Glomus fasciculatum, Glomus intraradices, and Glomus macrocarpum to determine effects of vesicular-arbuscular mycorrhizal fungi (VAMF) species on plant growth and mineral nutrient uptake. Sorghum root colonization by VAMF and plant responses to Glomus species were temperature dependent. G. macrocarpum colonized sorghum roots best and enhanced plant growth and mineral uptake considerably more than the other VAMF species, especially at 30°C. G. fasciculatum enhanced shoot growth at 20 and 25°C, and mineral uptake only at 20°C. G. intraradices depressed shoot growth and mineral uptake at 30°C. G. macrocarpum enhanced shoot P, K, and Zn at all temperatures, and Fe at 25 and 30°C above that which could be accounted for by increased biomass. Sorghum plant growth responses to colonization by VAMF species may need to be evaluated at different temperatures to optimize beneficial effects.     

Differential influence of native and introduced arbuscular mycorrhizal fungi on growth of dominant and subordinate plants

The impact of arbuscular mycorrhizal fungi (AMF) on plant ecosystems has been intensively reported. In this research, we explored the difference between native and introduced AMF in promoting the growth of dominant and subordinate plant species. In glasshouse experiments, dominants and subordinates from subtropical grasslands were colonized by native AMF or introduced AMF, Glomus versiforme. The biomass revealed that mycorrhizal dependencies (MD) on the native AMF of the dominants were much higher than those of the subordinates, while MD on the introduced AMF changed following the replacement of native AMF with introduced AMF. A close relationship between biomass promotion and increase in phosphorus uptake was observed, indicating the important role of AMF-enhanced nutrient acquisition by roots. Our results show that plant community structures are partly determined by MD on native AMF, and could be modified by introducing exogenous AMF species.     

FRS2 alpha 2F/2F mice lack carotid body and exhibit abnormalities of the superior cervical sympathetic ganglion and carotid sinus nerve

The docking protein FRS2α is an important mediator of fibroblast growth factor (FGF)-induced signal transduction, and functions by linking FGF receptors (FGFRs) to a variety of intracellular signaling pathways. We show that the carotid body is absent in FRS2α^2F/2F mice, in which the Shp2-binding sites of FRS2α are disrupted. We also show that the carotid body rudiment is not formed in the wall of the third arch artery in mutant embryos. In wild-type mice, the superior cervical ganglion of the sympathetic trunk connects to the carotid body in the carotid bifurcation region, and extends thick nerve bundles into the carotid body. In FRS2α^2F/2F mice, the superior cervical ganglion was present in the lower cervical region as an elongated feature, but failed to undergo cranio-ventral migration. In addition, few neuronal processes extended from the ganglion into the carotid bifurcation region. The number of carotid sinus nerve fibers that reached the carotid bifurcation region was markedly decreased, and baroreceptor fibers belonging to the glossopharyngeal nerve were absent from the basal part of the internal carotid artery in FRS2α^2F/2F mutant mice. In some of the mutant mice (5 out of 14), baroreceptors and some glomus cells were distributed in the wall of the common carotid artery, onto which the sympathetic ganglion abutted. We propose that the sympathetic ganglion provides glomus cell precursors into the third arch artery derivative in the presence of sensory fibers of the glossopharyngeal nerve.     

梅根际丛枝菌根真菌三个中国新记录种

Three new Chinese records, Acaulospora paulinae, Glomus aureum, and Pacispora robigina were found in a survey of arbuscular mycorrhizal fungi associated with Prunus mume in China. They were redescribed and illustrated in accordance with Chinese materials. These specimens were stored in the Herbarium Mycologicum Academiae Sinicae (HMAS) in Beijing.     

摩西管柄囊霉Funneliformis mosseae对连作大豆分枝期根系AM真菌群落结构的影响

本文研究摩西管柄囊霉Funneliformis mosseae对短期连作3个大豆品种分枝期根系AM真菌群落结构的影响,旨在探索不同大豆品种与AM真菌在连作土壤中的互作效应。通过向黑农44（HN44）、黑农48（HN48）和恳丰16（KF16）3个大豆品种盆栽土壤中接种F. mosseae,对接菌连作0年（未连作对照组）、连作1年、连作2年土壤中的大豆根系,采用Nested-Program Control Register-DGGE技术分析。结果表明,接种F. mosseae后,不同大豆品种根系AM真菌多样性指数和丰度值表现为连作2年的土壤>连作1年的土壤>未连作的土壤;其中,球囊霉属Glomus和F. mosseae为3个大豆品种根系中AM真菌的优势菌群。接种F. mosseae对连作1年、连作2年3个大豆品种根系AM真菌群落结构具有显著影响。     

丛枝菌根真菌四个中国新记录种

从梅和滨海植物根区土壤中分离得到丛枝菌根真菌4个中国新记录,即沙生球囊霉Glomus arenarium、莫顿球囊霉G. mortonii、三壁球囊霉G. trimurales和苍耳管柄囊霉Funneliformis xanthium。对其形态特征进行重新描述和图解。这4个种的标本保存在中国科学院菌物标本馆（HMAS）和厦门市园林植物园标本馆中。     

Effect of the arbuscular mycorrhizal symbiosis upon uptake of cesium and other cations by plants

Pot experiments were set up to determine the species-specific uptake of cesium (Cs) by mycorrhizal (AM) and non-mycorrhizal (non-AM) plants. Using stable Cs and K application, side-effects of mineral fertilization (K) on AM development and uptake of Cs and the other cations Na, Ca and Mg were investigated. AM colonization by the fungus Glomus mosseae led to a significant decrease in shoot Cs content of Agrostis tenuis from the first (4 weeks) to the third harvest (8 weeks). With regard to the root system, statistically significant differences were observed from the first (4 weeks) to the second harvest (6 weeks). Supply of additional K produced a significant decrease in Cs uptake by both AM and non-AM plants over a 10-week period. In the case of AM plant shoots, K fertilization did not very effectively reduce Cs uptake by A. tenuis. Cs contents of fertilized AM roots were similar to non-AM controls. Potassium application resulted in an increase in K content and a slight reduction in Na and Mg contents of shoots and roots. Without K fertilization, the Na content of non-AM controls was significantly enhanced over AM shoots. Shoot and root Ca contents were generally higher without than with K addition. Negative side-effects of K fertilization as a countermeasure to Cs uptake were not observed in relation to AM development. The intensity of colonization by G. mosseae was not significantly depressed by K treatment. AM development in plants appeared to decrease Cs uptake, at least at moderate nutrient levels. It is possible that Cs is sequestered by AM extraradical fungal hyphae and consequently not transferred to the plant to the extent found in non-AM roots. Accepted: 6 November 2000     

Are there benefits of simultaneous root colonization by different arbuscular mycorrhizal fungi?

Arbuscular mycorrhizal fungal (AMF) communities were established in pots using fungal isolates from a single field in Switzerland. It was tested whether multispecies mixtures provided more phosphorus and supported greater plant growth than single AMF species. Two host plants, medic (Medicago truncatula) and leek (Allium porrum), were inoculated with three AMF species (Glomus mosseae, G. claroideum and G. intraradices), either separately or in mixtures. The composition of the AMF communities in the roots was assessed using real-time PCR to determine the copy number of large ribosomal subunit genes. Fungal communities in the roots were usually dominated by one AMF species (G. mosseae). The composition of the communities depended on both plant identity and the time of harvest. Leek colonized by a mixture of G. claroideum and G. intraradices acquired more P than with either of the two AMF separately. Direct evidence is provided for functional complementarity among species within the AMF community colonizing a single root system. Competition among the species poses a major challenge in interpreting experiments with mixed inoculations, but this is greatly facilitated by use of real-time PCR.     

Genetic structure of arbuscular mycorrhizal populations in fallow and cultivated soils

The impact of fallowing on the genetic structure of arbuscular mycorrhizal fungi (AMF) was studied by hierarchical sampling of spores from four plots in a fallow and a cultivated field. A nested multiplex PCR approach was used to assign the spores to genotypes. Variable introns of the two protein-coding genes GmFOX2 and GmTOR2 were used as co-dominant genetic markers together with the large subunit (LSU) rDNA. The gene diversity and genetic structure of Glomus mosseae, Glomus geosporum and Glomus caledonium were compared within and between the fields. Spores of G. caledonium and G. geosporum were more abundant in the cultivated field, whereas G. mosseae was more frequent in the fallow field. The number of genotypes was not different between the two fields. Analysis of gene diversity of G. caledonium in the fallow field indicated that a larger part of the heterogeneity could be attributed to variation between plots rather than subplots, suggesting that the lack of soil cultivation resulted in more heterogeneous population genetic structures. Analyses of haplotype networks of the fungi suggested a subdivision of G. mosseae haplotypes between the two fields, whereas no such division was seen in G. geosporum and G. caledonium. The results show that agricultural practices differently affect both the abundance and the population structure of different AMF species.