Trapping of phosphate solubilizing bacteria on hyphae of the arbuscular mycorrhizal fungus Rhizophagus irregularis DAOM 197198

A simple method is described for trapping phosphate solubilizing bacteria (PSB) strongly attached to the hyphae of the arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis (Ri). Bacteria were isolated from the hyphosphere of mycorrhizal leek plants growing on Turface previously inoculated with soil suspensions, obtained from the mycorrhizosphere of mycorrhizal plants growing in agricultural settings or maple forests in Quebec, Canada. Among the best PSB strongly attached to the hyphae of Ri, 26 isolates belonged to Burkholderia spp. and one was identified as Rhizobium miluonense. Four hyphobacteria exhibiting high potential of inorganic and organic P mobilization were further compared with four equivalent mycorrhizobacteria directly isolated from mycorrhizospheric soils sampled. In general, hyphobacteria were superior in mobilizing P from hydroxyapatite and from a low reactivity igneous phosphate rock from Quebec. Release of gluconic acid or the product of its oxidation 2-ketogluconic acid, are the main mechanisms involved in P solubilization. In a two compartments Petri plate system, Ri extraradical hyphal exudates, supported PSB growth and activity. In the absence of PSB Ri showed a negligible P solubilization activity. In the presence of PSB a substantial increase in P mobilization was observed, and the superiority of hyphobacterial activity was also observed under this system. Our results suggest that in developing a bioinoculant based on selected PSB, their interaction with AMF hyphae should not be overlooked.     

大学“农民工”子女的现状与学习动机分析

大学农民工子女的现状不容乐观,这既是当前高等教育深层次改革中遇到的新的理论问题,又是新的实践问题,积极探索其解决的办法,对促进社会和谐,培养德智体全面发展的人具有积极的意义。     

Limitations to using benomyl in evaluating mycorrhizal functioning

Arbuscular mycorrhizal (AM) grasses compete for nutrients with ectomycorrhizal (EM) pine in the southeastern United States. Our objective was to determine if benomyl could be used to selectively inhibit the function of AM and thereby reduce grass competition in the field. The effects of Benlate (active ingredient: benomyl) in the greenhouse and field were evaluated. No effect was observed on pine inoculated with Pisolithus tinctorius in the greenhouse. Colonized root length of benomyl-treated Zea mays L. plants inoculated with Glomus sp. in the greenhouse remained static over time and the response was not dose dependent at concentrations of 0, 20, 60 and 150kg benomyl ha^–1 equivalent. In contrast, colonization of nontreated plants increased over time. In the field, a minimal reduction of grass colonization was observed following four applications of benomyl ranging from 5 to 20kgha^–1. We conclude that benomyl can successfully inhibit development of AM fungi under controlled conditions in the greenhouse with no inhibitory effects on the EM fungus P. tinctorius; however, in the field several factors may interfere with the effect of benomyl on AM fungi. These factors include: (a) the presence of ground cover which obstructs penetration of the fungicide to the soil, (b) timing of application in relation to mycorrhizal development, and (c) the application method of benomyl, a soil drench being preferable to a foliar spray. Received: 30 September 1996     

The effects of live and dead roots on soil fungi in spodosolic soils of the New Jersey Pinelands

The effects of live and dead roots on soil fungi were investigated experimentally in a spodosolic soil of the New Jersey Pinelands. Field mesocosm plots were constructed to have a layer of either C- and N-rich organic soil or a vermiculite substitute overlying a layer of sandy mineral soil with a very low organic content. The plots were also supplied with live pitch pine and blueberry roots or dead pitch pine roots in varying quantities based on anturally occurring densities (half, same, and double the ambient quantities). All plots were sampled 1 year after construction (June 1991), and three more times in two subsequent years (November 1991, June 1992, June 1993). In the presence of live roots, fluorescein diacetate-determined (FDA-active) fungal hyphae, total fungal hyphae, and soil moisture decreased significantly in the organic material, while no change was associated with the dead roots. The FDA-active fungal length in the live-root plots ranged from 40 to 165 mg^-1 soil, and from 55 to 335 mg^-1 soil in the dead-root plots. While the total fungal length in live-root plots remained constant over time (3000 mg^-1 soil), the total fungal length in the dead-root plots increased from an initial value of 3000 to >4000 mg^-1 soil at the conclusion of the study. Fungal lengths in mineral soil were higher under organic material than under the vermiculite substitute. Soil moisture was higher in the presence of live roots in mineral soils, but this did not increase the fungal abundance. Inputs of dead roots did not alter the fungal abundance. Overall, we demonstrated that live and dead roots had different effects on fungal abundance in soils with contrasting qualities, and in a spodosolic forest soil, roots could have ecosystem effects very different from those in agricultural soils.Contribution No. 94-29 from the Institute of Marine and Coastal Sciences     

Comparisons of vesicular-arbuscular mycorrhizal species and inocula formulations in a commercial nursery and on diverse Florida beaches

For efficient use of mycorrhizal inoculum the effectiveness of the isolate used and the rate of application required for maximum colonization must be known. The objectives of this research were to (1) define the lower limit of inoculum density required for maximum colonization of Uniola paniculata in a commercial nursery and (2) evaluate the performance of a selected native dune vesicular-arbuscular mycorrhizal (VAM) isolate versus a commercially available non-dune VAM (foreign) isolate on three diverse Florida beaches. An inoculum-dilution study was conducted in a commercial nursery with cutroot inoculum of a Glomus sp. that had been isolated from a Florida dune. Maximum colonization was achieved with approximately 1 propagule ml^-1 of growth medium. In a separate nursery study, 10 inoculation treatments (combinations of inoculum source and level) were established in the commercial nursery. Treatments included cut-root and sheared-root inoculum of the native dune isolate, and Nutri-Link, a commercial inoculum of G. intraradices. Colonized plants from selected treatments were transplanted to beach sites around Florida. At Miami Beach, after one growing season, the shoot mass of plants inoculated with the native isolate was approximately twice that of plants inoculated with the foreign isolate. At Katherine Abbey Hanna Park and Eglin Air Force Base there were no significant inoculum source effects on shoot mass or root length after one growing season. However, the native isolate produced a greater colonized root length than the foreign isolate in all plantings. The soil hyphal density was measured at Eglin Air Force Base, and the results showed that plants inoculated with the native isolate had more soil hyphae (4.33 mg^-1) than plants inoculated with the foreign isolate (3.65 mg^-1) or the non-inoculated plants (2.12 mg^-1). Even where there were no obvious shoot growth responses, mycorrhizal inoculation may have an important effect on dune stabilization, as soil hyphae are known to bind sand grains and improve dune stability.Publishedas Florida Agriculture Experiment Station Journal SeriesPublishedas Florida Agriculture Experiment Station Journal Series     

60Co-γ射线辐照菌丝选育多糖高产菌株

采用^60Co—γ射线诱变茵丝，在辐照剂量为1000Gy，剂量率为67．8Gy／h的条件下，经过拮抗试验和酯酶同功酶电泳验证，选育出一株巴西蘑菇新菌株。经液体培养其胞外多糖产量较出发菌株提高12％。     

五室隔板法研究三叶草根间菌丝桥磷传递的可行性

应用五室隔板法研究了三叶草根间菌丝桥对32P的传递作用。结果表明，菌根侵染供体植株根系之后，可以穿过隔板再度侵染受体植株的根系，从而形成植株根系之间的菌丝桥。这一菌丝桥将施用在供体植株的32P运输到受体植株。表明五室隔板法可以在排除其他养分传递途径的情况下用以研究三叶草植株根间菌丝桥在32P传递中作用。     

紫外线诱导对药用真菌菌丝体生长的影响

用紫外线照射羊肚菌、松茸、金针菇菌丝体，研究了不同照射时间对菌丝生长速度、菌落直径、菌丝生长势及菌丝干重的影响。结果表明：紫外线照射对羊肚菌和松茸菌丝体的生长有不同程度的促进作用，其中以照射4min处理组的作用最明显，且松茸菌丝体的生长（P＜0．05－P＜0．001）比羊肝菌（P＜0．05－P＜0．01）强；紫外线照射对金针菇菌丝体的生长有显著的抑制作用（P＜0．001）。     

Mycorrhizal function on soil aggregate stability in root zone and root-free hyphae zone of trifoliate orange

Arbuscular mycorrhizal fungi (AMF) influence soil aggregate stability through their hyphae, roots, and glomalin-related soil protein (GRSP); however, the individual effect of these factors is difficult to distinguish. Pots separated by a 37-μm mesh bag buried in the middle of each pot was used to establish root zone (root + hyphae) and hyphae zone (roots free), where the Poncirus trifoliata seedlings were colonized by Funneliformis mosseae or Paraglomus occultum in root zone. AMF inoculation significantly increased shoot, root, and plant’s total biomass, soil organic carbon, GRSP fractions, 2–4 and 1–2 mm size water-stable aggregates, and mean weight diameter (MWD) in root or hyphae zone. Within root zone, root colonization and biomass presented stronger relationship with MWD than GRSP fractions. While, within hyphae zone, total of GRSP fraction was significantly correlated with MWD. The study, suggested further that root biomass and colonization were the main mechanisms in root zone for improving aggregate stability, whereas total of GRSP fractions was of paramount importance in hyphae zone. Mycorrhizal effect on aggregate stability was observed to be contrastingly different between root zone and hyphae zone.