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| 2007 | 2006 | 2005 | 2004 | 2003 | 2002 | 2001 | 2000 | 2002 * * * * * * * * * * * * * * * * * * * * * * * Author : Sebastian Fracchia Author: Xinhua He Nitrogen (N) exchange mediated through common mycorrhizal networks (CMNs) was investigated in pure and mixed systems of Casuarina cunninghamiana and Eucalyptus maculata, and Glycine max (soybean) and Sorghum bicolour (sorghum). Both 15N labeling and 15N natural abundance (d15N) studies were performed. Seeds of all four species were aseptically germinated with or without mycorrhizal fungi or N2-fixing bacteria on agar media in petri dishes. Seedlings were transplanted into three-compartment growth units and paired. 37 µm diameter nylon mesh, RainSaver crystals (high water holding capacity) and N-serve (nitrification inhibitor) prevented direct root contact, soil nutrient flow with water and nitrification, respectively. At harvest, none of the controls was mycorrhizal or nodulated, while all originally non-mycorrhizal seedlings were colonised. Mycorrhizal hyphae penetration through the nylon mesh was directly observed and demonstrated with an Environmental Scanning Electron Microscope (ESEM). Colonisation of roots as high as 80% confirmed that common ectomycorrhizal or arbuscular mycorrhizal networks were established between pairs in all combinations. Mycorrhization had significant effects on biomass production in both N2-fixing plants (Casuarina, soybean) and non-N2-fixing ones (Eucalyptus, Sorghum). Dry matter production was highest in both partners when N2-fixing plants were mycorrhizal and nodulated. However, mycorrhization had little impact on N accumulation in eucalypts, but had a major effect in casuarinas, despite eucalypts having nearly double the colonisation rate. Biomass was positively correlated with tissue N content in both species. The nodulated mycorrhizal casuarinas and their companion mycorrhizal eucalypts had the highest tissue N accumulation. Both biomass and total N in all N-receivers equalled those in N-donors, especially when nodulated casuarinas were N-receivers. The above trends were generally true for soybean and sorghum pairs. In addition, d15N values were negative in nodulated casuarinas, but positive in nodulated soybeans. Biological nitrogen fixation (BNF) contributed up to 50% and 40% of N in nodulated mycorrhizal casuarinas and soybeans, respectively. From both 15N labelling experiments and d15N analyses it was established that N-transfer occurred bidirectionally (two-way) between Casuarina and Eucalyptus, and between soybean and Sorghum. The percentages and amounts of N transferred, and the % of N in the receiver derived from the transfer (%NDFT) were generally significantly higher in the nodulated/mycorrhizal pairs than in the non-nodulated/mycorrhizal pairs. This occurred regardless of whether the nodulated N2-fixing plants were 'N-donors' or 'N-receivers'. However, the %NDFT was always on the same scale regardless of the direction of N-transfer. The % and amount of N-transfer were also significant from non-N2-fixing plants to nodulated N2-fixing plants (with up to 50% biological N2-fixation) rather than the reverse. Significantly higher bidirectional and net N-transfer were also found between the sole mycorrhizal and the nodulated/mycorrhizal pairs. These results indicated a net gain in N by N2-fixing plants, but not by non-N2-fixing ones. The similar N transferred to non-N2-fixing plants and to N2-fixing ones in the sole mycorrhizal pairs indicated that two-way N-transfer could occur naturally between any mycorrhizal plants, regardless of whether they were N2-fixing plants or non-N2-fixing ones, and that N resources could equally be reallocated between plants through mycorrhizae. The significantly greater intensity of bidirectional N-transfer in the nodulated mycorrhizal pairs showed that more substantial amounts of N could be shuttled between plants because of a generally greater physiological and ecological N demand in low-external-N-input conditions. These results therefore suggest that N2-fixing capacity might not be a prerequisite for, but might affect the intensity of, this two-way N-transfer. In addition to accessing N from soils directly by roots, the experiments suggest that N2-fixing plants have two further strategies, N2-fixation and mycorrhization, to satisfy their high N-demand, while mycorrhization alone can meet the needs for relatively low N-demand by non-N2-fixing plants. Two 'mycocentric' N-transfer mechanisms are postulated to account for these differences. It seems that any plant that gives more N than it receives is an 'N-donor', while the opposite is true for an 'N-receiver'. If these mechanisms operate as these experiments have demonstrated and prove to be widespread, ideas about mycorrhiza-mediated N exchange and cycling in both agricultural and natural ecosystems may have to be re-evaluated, and concepts about nutrient cycling and energy exchange in plant communities may also have to be reformulated. Bidirectional N-transfer certainly has important implications for the nitrogen economy of N2-fixation-based agricultural and natural ecosystems. In such ecosystems, the magnitude of mycorrhiza-mediated N-transfer and N movement seems to be determined by the dynamic four-way interactions between plant roots, mycorrhizal fungi, N2-fixing bacteria, and N resource availability and requirements. Author: Rana S. K. In uplands of eastern Chotanagpur plateau (agro-climatic zone no. 12), the target ecosystem, rice is grown during wet season as rainfed crop. The crop is direct sown and grown under aerobic soil conditions. Aerobic soil conditions are favorable for activity of arbuscular mycorrhizal fungi. Though the ecosystem is not very conducive for rice cultivation, it is grown by the farmers as subsistence farming due to socio-economic need. Upland rice is grown at very poor yield level of 0.5-1.0 t/ha in Chotanagpur plateau (Jharkhand). One of the major constraints of poor rice productivity is inefficient phosphorus acquisition by rice. Having these information, attempts were made in the present investigation to explore possibilities of enhancing colonization of native arbuscular mycorrhizal fungi in upland rice for better phosphorus nutrition. This was tried by introducing several AMF susceptible crops in the upland rice based cropping systems. While selecting the rice based cropping systems and the crops, proper care was taken to suite the target ecosystem and farmers requirements. Prior to initiating various laboratory based analysis related to arbuscular mycorrhizal fungi and associated phosphorus uptake, the standard techniques were further standardized to suit specific requirement of the present investigation. The present investigation consisted of three aspects including (i) colonization pattern of native arbuscular mycorrhizal fungi (AMF) in upland rice, (ii) native arbuscular mycorrhizal association pattern and associated phosphorous uptake in upland rice under rice-legumes intercropping systems and (3) native arbuscular-mycorrhizal association pattern and associated phosphorus uptake(by upland rice) under rice based relay and sequence cropping systems. The following results were obtained.
Author: Seak-Jin Kim Title: Investigation on methods for recultivation of problematic sites in South Korea under consideration of different mycorrhizal associations and various soil substrats. Degree: Ph D Year: 2002 Language: German Institution: University of Bremen (UFT), Plant Physiology and Plant Anatomy, Leobener Strasse, D-28359 Bremen, Germany Key-Words: reforestation, symbiosis, inoculation, nutrient, heavy metal, rubble, Pinus thunbergii, P. densiflora, Pisolithus tinctorius, Suillus bovinus, Rhizopogon roseolus. Supervisor: Heyser, W. E-Mail: kim@uni-bremen.de Summary: The aim of the present investigation was the development of a model system for an improvement of a reforestation of extreme sites. As extreme locations here in particular, waste dumps, rubble and eroded locations in South Korea were considered. Two domestic Pinus species (P. thunbergii and P. densiflora) of South Korea and as mycobionts Pis. tinctorius and S. bovinus and a field isolate of R. roseolus were selected. As soil substrates mainly forest soil, sand, and rubble were tested. Additionally, compost was used as an additive to improve the used soil substrates. In the present work a special emphasis was placed on the choice of efficient symbiotic partners. This work contains: development and optimization of an method to isolate and to produce suitable axenic cultures from fruit bodies and mycorrhizal roots from the field, identification of field mycorrhizas by a molecular technique (ITS-PCR), development of an in-vitro method to establish mycorrhizas by different inoculation techniques e. g. the "nylon mesh " and the "petri dish method", tests for an efficient inoculation technique with liquid cultures, in order to achieve a high number of inoculated plants, test of the effect of different soil substrates (mixture on sand, rubble and compost) on growth and mycorrhizal colonization of different mycorrhizal tree seedlings (Pis. tinctorius, S. bovinus and R. roseolus), light and scanning electron microscopical investigations of the development of the symbiosis, anatomy and morphology of mycorrhizal tree roots and documentation of the mycorrhizal formation process, determination of different soil parameters, e. g. nutrient and toxic element concentrations (heavy metals) by atomic absorption-spectroscopy (AAS) of the different soil substrates and the different plant organs (shoot and root) of mycorrhizal and non-mycorrhizal pine seedlings. An important component of this work was the optimization of methods to isolate mycorrhizal fungi from the field, whose pH optimum ranges from neutral to slightly alkaline. The extraction of axenic cultures from fruit bodies and mycorrhizal roots from the field by use of the optimized isolation technique were successful. For the mycorrhiza inoculation in different soil substrates, especially a field isolate of the mycorrhizal fungus R. roseolus was used, since it showed a good growth on MMN medium and a rapid colonization of the plants studied. By a molecular biological based identification method (ITS-PCR), the fungal species isolated from fruit bodies (Pax. involutus and Suillus luteus) and directly from mycorrhizal roots (R. roseolus) was identified. In order to obtain a good mycorrhizal colonization, different inoculation methods, e. g. the "nylon mesh method" and "petri dish method" were tested". With the "nylon mesh method" a rapid and effective mycorrhiza colonization was achieved, but this method differed not from the "petri dish method" used in further attempts with respect to the selected soil substrates and symbiotic partners. In a model system, the plants (P. thunbergii and P. densiflora) were successfully inoculated with liquid cultures of Pis. tinctorius and R. roseolus, in order to examine which tree species can good be colonized and show an optimal plant growth under the experimental conditions. The results showed that P. thunbergii plants inoculated with R. roseolus showed a higher shoot and root growth and a better mycorrhizal colonization than P. densiflora. With the mycorrhizal fungus R. roseolus, a better mycorrhizal colonization rate in the sand/rubble/compost mixture could be obtained than with the mycorrhizal fungi Pis. tinctorius and S. bovinus. Mycorrhizal plants showed generally a better shoot and root growth than non-mycorrhizal control plants. The development of the symbiosis based on morphological and anatomical differences of mycorrhizal and non-mycorrhizal roots (P. thunbergii/Pis. tinctorius) were presented and their development on the different soil substrates, forest soil, sand and rubble, is discussed. Concerning the development of the roots and the establishment of the mycorrhizal fungi within roots in forest soil, sand and building debris, morphological differences of the formation of the hyphal sheath and the Hartig net within the mycorrhizal root cortex were determined. In order to be able to determine the effect of soil parameters on the development of the mycorrhiza and on plant growth, different soil parameters as well as nutrient and toxic element (e.g. heavy metals) concentrations in shoots and roots of mycorrhizal and nonmycorrhizal plants (P. thunbergii/Pis. tinctorius) were determined. The growth of the pine seedlings differed dependent on the soil substrate. There was a remarkably reduced shoot growth of the seedlings cultured in sand, which is obviously due to the low nutrient contents of this substrate. However, also in rubble and rubble/sand mixtures, which contained high levels of nutrients and toxic elements (heavy metals), a clearly reduced shoot and root growth was observed compared to the control grown on forest soil. Especially on rubble and rubble/sand mixtures mycorrhizal plants showed remarkably higher shoot and root dry weights than the nonmycorrhizal plants. The developed model system was useful for the answering of different questions. The effect of the mycorrhizal formation on the inoculation attempts, and the optimal combination of various symbiotic partners are also detected here. In the majority of the investigations, the positive effect of efficient mycorrhizal fungi for the tree growth was obvious. A purposeful and optimized selection of mycorrhizal fungi could lead to an improved plant growth on extreme sites. Teste, P. F. 2002. Ectomycorrhizal status and growth of Interior Douglas-fir on degraded reforestation sites. M.Sc. thesis. Simon Fraser University, Burnaby. Supervisor: Margaret G. Schmidt INGRID van AARLE: The Ecophysiology of Arbuscular Mycorrhizal Fungi: Phosphatase Activity Associated with Extraradical and Intraradical Mycelium. PhD thesis, Microbial Ecology, Lund University, Sweden.
Author: Lynn Whitfield Yokomizo, N. K. S. Soil solarization of Pinus elliottii Engelmann var. elliottii seedlings substrate: effects on weeds, fungi and bacterial population, with emphasis on ectomycorrhizas and Pisolithus tinctorius (Mich. e Pers.) Coker & Couch and Suillus luteus (L. ex Fr.) Gray inoculants. 2002.118p. PhD Thesis in Biological Science. Instituto de Biocięncias, Universidade Estadual Paulista, Rio Claro, Brazil. 2002. Abstract
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