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  • Biological sciences -- Biology -- Botany
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  • 1
    Language: English
    In: Plant and Soil, 2013, Vol.364(1), pp.341-355
    Description: Aims: The aim was to quantify the nitrogen (N) transferred via the extra-radical mycelium of the arbuscular mycorrhizal fungus Glomus intraradices from both a dead host and a dead non-host donor root to a receiver tomato plant. The effect of a physical disruption of the soil containing donor plant roots and fungal mycelium on the effectiveness of N transfer was also examined. Methods: The root systems of the donor (wild type tomato plants or the mycorrhiza-defective rmc mutant tomato) and the receiver plants were separated by a 30 mu m mesh, penetrable by hyphae but not by the roots. Both donor genotypes produced a similar quantity of biomass and had a similar nutrient status. Two weeks after the supply of super(15)N to a split-root part of donor plants, the shoots were removed to kill the plants. The quantity of N transferred from the dead roots into the receiver plants was measured after a further 2 weeks. Results: Up to 10.6 % of donor-root super(15)N was recovered in the receiver plants when inoculated with the arbuscular mycorrhizal fungus (AMF). The quantity of super(15)N derived from the mycorrhizal wild type roots clearly exceeded that from the only weakly surface-colonised rmc roots. Hyphal length in the donor rmc root compartments was only about half that in the wild type compartments. The disruption of the soil led to a significantly increased AMF-mediated transfer of N to the receiver plants. Conclusions: The transfer of N from dead roots can be enhanced by AMF, especially when the donor roots have been formerly colonised by AMF. The transfer can be further increased with higher hyphae length densities, and the present data also suggest that a direct link between receiver mycelium and internal fungal structures in dead roots may in addition facilitate N transfer. The mechanical disruption of soil containing dead roots may increase the subsequent availability of nutrients, thus promoting mycorrhizal N uptake. When associated with a living plant, the external mycelium of G. intraradices is readily able to re-establish itself in the soil following disruption and functions as a transfer vessel.
    Keywords: Arbuscular mycorrhiza ; Reduced mycorrhizal colonisation (rmc) mutant ; Extra-radical mycelium ; Root turnover ; Solanum lycopersicum
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 2
    Language: English
    In: Plant and Soil, 2013, Vol.372(1), pp.361-374
    Description: Issue Title: In Memory of Horst Marschner This study aimed to determine the effect of arbuscular mycorrhizal (AM) fungi and phosphorus (P) supply levels on [beta]-carotene concentrations in sweet potato (Ipomoea batatas L.) tubers. Two commercial AM fungal isolates of Glomus intraradices (IFP Glintra) and Glomus mosseae (IFP Glm) which differ in their life cycles were used. Sweet potato plants were grown in a horizontal split-root system that consisted of two root compartments. A root-free fungal compartment that allowed the quantification of mycelial development was inserted into each root compartment. The two root compartments were inoculated either with the same or with different AM isolates, or remained free of mycorrhizal propagules. Each fungal treatment was carried out in two P supply levels. In the low P supply level, mycorrhizal colonization significantly increased [beta]-carotene concentrations in sweet potato tubers compared with the non-mycorrhizal plants. Glomus intraradices appeared to be more efficient in increasing [beta]-carotene concentrations than G. mosseae. Dual inoculation of the root system with the two mycorrhizal fungi did not result in a higher increase in tuber [beta]-carotene concentrations than inoculation with the single isolates. Improved P nutrition led to higher plant tuber biomass but was not associated with increased [beta]-carotene concentrations. The results indicate a remarkable potential of mycorrhizal fungi to improve [beta]-carotene concentrations in sweet potato tubers in low P fertilized soils. These results also suggest that [beta]-carotene metabolism in sweet potato tubers might be specifically activated by root mycorrhizal colonization.[PUBLICATION ]
    Keywords: β-carotene ; Glomus intraradices ; Glomus mosseae ; Phosphorus ; Sweet potato
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 3
    Language: English
    In: Plant and Soil, 2002, Vol.243(2), pp.209-217
    Description: Nutrient concentrations in the rhizosphere soil can be higher, lower or remain unchanged compared to the bulk soil, but relatively little is known about such changes for basic cations in the rhizosphere of tree roots. A modified root container technique of studying rhizosphere processes was employed. Plexiglas cylinders were horizontally split by a membrane with 30 μM mesh size into an upper compartment for root growth and a root-free lower compartment, each with an inner diameter of 5 cm and a height of 10 cm. One 2-year-old Norway spruce ( Picea abies) seedling was transplanted from a nursery into each cylinder. Plants were not specifically inoculated, but roots were colonised by a mix of ectomycorrhizal fungi originating from the nursery. The nutrient poor mineral soil used in the experiment was taken from a forest site in Bayerischer Wald, southern Germany. The soil was either supplied with a mix of Ca, Mg and K, or not supplied with these cations. Plants were harvested 30 weeks after transplanting. The nylon membrane between the root compartments restricted root growth to the upper compartment, so that by the end of the experiment a root mat was formed at the top side of the membrane. In the lower compartment, soil nearest to the root mat was regarded as rhizosphere soil while soil in a distance from the root mat was regarded as bulk soil. In the upper compartment, rhizosphere soil was obtained at the end of the experiment by gently shaking the roots. The soils were analysed for Ca, Mg and K contents following two different soil extraction methods. In the fertilised treatment, H 2 O-extractable Ca and Mg were accumulated in the rhizosphere. In contrast, K (NH 4 Cl-extraction) was depleted in the rhizosphere. In the bottom tube, the depletion of K (NH 4 Cl-extraction) was restricted to 1 cm distance from the root mat. In unfertilised soil, Ca, Mg and K concentrations did not differ clearly between rhizosphere and bulk soils. The results indicated that the occurrence of cation gradients in the rhizosphere depended on the level of soil nutrient supply. Distinct rhizosphere effects were measured by conventional soil extraction methods only when the soil was freshly fertilised with mineral elements prior to the experiment. In this case, K depletion in the rhizosphere reflected higher K uptake by the fertilised Norway spruce plants. For low-nutrient soils, novel techniques are required to follow subtle changes in the rhizosphere.
    Keywords: calcium ; cation supply ; extractable cations ; magnesium ; Norway spruce ; potassium ; rhizosphere chemistry
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 4
    Language: English
    In: Plant and Soil, 2009, Vol.322(1), pp.209-218
    Description: Micro-suction cups were installed in split-root rhizotrons to investigate changes of ion concentrations pertaining to different root zones (Norway spruce) or various root types (Douglas-fir). Plant seedlings were grown in mineral soils fertilised with a mix of KMgCa or unfertilised. In Norway spruce, ions accumulated mostly in the rhizosphere near root tips in fertilised soil. Cations (Fe 3+ /Mn 2+ , Na + ) and anions (Cl - , SO 4 2- ) were depleted in basal root areas in unfertilised soil. In Douglas-fir, ion accumulations (except K in unfertilised soil) occurred in rhizosphere of current-year suberized roots in both fertilised and unfertilised soils. Ion concentrations in rhizosphere of one-year-old suberized roots were highest compared to those of newly-grown or current-year roots in fertilised soil. These data demonstrate that soil solution chemistry clearly differs in rhizosphere of different segments of single roots and various root types. Ion accumulation in rhizosphere may be due to high mass flow transport of ions to root surfaces, and the accumulation of ions in rhizosphere was more distinct for root tips.
    Keywords: Coniferous seedlings ; Ion concentrations ; Micro-suction cups ; Rhizosphere
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 5
    In: New Phytologist, May 2005, Vol.166(2), pp.601-609
    Description: •  We investigated the growth and nutrient uptake of the Lycopersicon esculentum symbiosis mycorrhiza‐defective plant mutant rmc, challenged with arbuscular mycorrhiza (AM) fungal propagules, in the presence or absence of roots of the commercial wild‐type tomato cv. Golden Queen (GQ). •  Two plants shared the middle (combi) compartment of a horizontal three‐compartment split‐root pot with one part of their root system; the other part was grown separately in an outer (solo) pot. Combinations of rmc and GQ plants were grown together in soil that was either mycorrhiza‐free (–M) or prepared with AM fungal inoculum (+M). •  Surface colonization of rmc roots was strongly increased in the presence of (+M) GQ roots. AM fungal inoculation increased phosphorus uptake of GQ plants, but decreased growth and P uptake of rmc plants. Growth and P uptake of (+M) GQ plants were reduced when plants were grown in combination with rmc rather than another GQ plant. •  AM fungi in the (combi) compartment may have preferentially formed hyphae spreading infection rather than functioning in P uptake in (+M) GQ plants grown in combination with rmc. Surface colonization of (+M) rmc roots, in the presence of GQ roots, was probably established at the expense of carbohydrates from associated GQ plants. Possible reasons for a decreased P uptake of rmc plants in response to AM fungal inoculation are proposed.
    Keywords: Arbuscular Mycorrhiza Am ; Inoculum Potential ; Phosphorus P Deficiency ; Plant Defence Response ; Mutant ; Symbiosis‐Defective Plant Mutants ; Tomato
    ISSN: 0028-646X
    E-ISSN: 1469-8137
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  • 6
    Language: English
    In: Plant and Soil, 2004, Vol.261(1), pp.245-255
    Description: The aim of the present study was to quantify the contribution of AMF to phosphorus (P) nutrition of the host plant when the P availability in the soil was limited by drought. To investigate the potential of AMF hyphae in taking up P from dry soil, mycorrhizal [+M] and nonmycorrhizal [−M] Sorghum bicolor L. plants were grown in a vertical split root system that consisted of two compartments placed upon one the other. The upper compartment was filled with well fertilised soil and the plant roots were allowed to grow into the lower compartment through a perforated bottom. The lower compartment was filled with an expanded clay substrate and nutrient solution, to supply the plants with water and all nutrients except P. The soil in the upper compartments was either dried [−W] or kept moist [+W] during a period of four weeks before harvest. The total plant P content did not differ significantly between the [−M] and the [+M] plants within the [+W] treatment. In contrast, the P content of the [+M] plants was almost twice as high as the [−M] plants when the soil in the upper compartment was dried. The concentrations of all elements except P in plant shoot tissue were sufficient for adequate plant growth. Phosphorus concentrations in the shoots of [−M/−W] plants indicated P deficiency, and these plants also had significantly lower dry matter and transpiration compared to the plants in all other treatments. From the results of the present experiment it can be concluded that mycorrhizal colonisation seems to be particularly benefical to P uptake from dry soil
    Keywords: Arbuscular mycorrhizal fungus ; partial soil drying ; phosphorus uptake ; Sorghum bicolor
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 7
    Language: English
    In: Plant and Soil, 1996, Vol.186(2), pp.361-369
    Description: The response of carbohydrate metabolism in 3-year-old Norway spruce plants to an increased amount of nitrogen supply to a N-poor forest soil was investigated in a pot experiment. After 7 months of treatment we found a decreased amount of starch in both needles and roots, together with decreased amounts of sucrose in needles of those plants grown under an enhanced inorganic N supply. In addition, the activity and the protein amount of the anaplerotic enzyme phospho enol pyruvate carboxylase (PEPC) and the activity of NADP-dependent isocitrate dehydrogenase (IDH) were clearly increased. The activity of sucrose phosphate synthase (SPS) and the pool size of fructose 2,6-bisphosphate (F26BP) were not affected by high supply of inorganic N. These data indicate a shift of carbon flow from starch formation towards an enhanced provision of carbon skeletons for N assimilation and shoot growth. In parallel, we found decreased contents of fungus-specific compounds (ergosterol, mannitol, trehalose) in roots, which are indicators of a decreased colonization by ectomycorrhizal fungi, probably as a result of a changed allocation and partitioning of photoassimilates due to an increased N supply.
    Keywords: ectomycorrhiza ; fungus-specific compounds ; isocitrate dehydrogenase ; nitrogen ; Picea abies ; phosphopyruvate carboxylase
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 8
    In: New Phytologist, November 1991, Vol.119(3), pp.397-404
    Description: To study phosphorus (P) depletion and soil pH changes at the root–soil interface (rhizosphere) and at the hyphaesoil interface, mycorrhizal and non‐mycorrhizal white clover ( L.) plants were grown for 7 wk in two sterilized soils (Luvisol and Cambisol) in pots comprising five compartments: a central one for root growth, two adjacent compartments, separated from the central compartment by a nylon net of 30 μm mesh size, for growth of vesicular‐arbuscular (VA) mycorrhizal [ (Nicol. & Gerd.) Gerdemann & Trappe] hyphae (hyphal compartments), and two outer compartments, separated from the hyphal compartments by a 0.45 μm membrane, which neither roots nor hyphae could penetrate (bulk soil compartments). Phosphorus was supplied as Ca(HPO) at a rate of 50 mg P kg soil in the root compartment and 150 mg P kg soil in the hyphal and bulk soil compartments. Nitrogen was supplied as (NH)SO at the rate of 300 mg N kg soil uniformly to all compartments. In both soils, shoot dry weight and P uptake were much higher in mycorrhizal plants compared with non‐mycorrhizal plants. Hyphae of VA mycorrhizal fungi contributed 70% (Cambisol) or 80% (Luvisol) to total P uptake of mycorrhizal plants. In the hyphal compartments, concentrations of both HO‐extractable soil P (Cambisol and Luvisol) and NaHCO‐extractable soil P (Luvisol) were decreased drastically. Soil P depletion profiles developed not only at the root‐soil interface (rhizosphere), but also at the hyphae‐soil interface and extended several millimetres from the hyphae surface into the soil. Likewise, the soil pH was decreased at the root‐soil interface, in the hyphal compartment and also at the hyphae‐soil interface. The results demonstrate that, similarly to roots, hyphae of VA mycorrhizal fungi have the ability to form a P depletion zone and a zone of altered pH in the adjacent soil. Thus, as well as at the root‐soil interface, soil conditions at the hyphae–soil interface may also differ considerably from conditions in the bulk soil.
    Keywords: Hyphae–Soil Interface Hyphosphere ; Phosphorus ; Soil Ph ; White Clover ; Va Mycorrhiza
    ISSN: 0028-646X
    E-ISSN: 1469-8137
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  • 9
    Language: English
    In: Plant and Soil, 1991, Vol.136(1), pp.41-48
    Description: To examine the influence of vesicular-arbuscular (VA) mycorrhizal fungi on phosphorus (P) depletion in the rhizosphere, mycorrhizal and non-mycorrhizal white clover ( Trifolium repens L.) were grown for seven weeks in a sterilized calcareous soil in pots with three compartments, a central one for root growth and two outer ones for hyphae growth. Compartmentation was accomplished by a 30-μm nylon net. The root compartment received a uniform level of P (50 mg kg −1 soil) in combination with low or high levels of P (50 or 150 mg kg −1 soil) in the hyphal compartments. Plants were inoculated with Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe or remained uninfected. Mycorrhizal inoculation doubled P concentration in shoot and root, and increased dry weight, especially of the shoot, irrespective of P levels. Mycorrhizal contribution accounted for 76% of total P uptake at the low P level and 79% at the high P level, and almost all of this P was delivered by the hyphae from the outer compartment. In the non-mycorrhizal plants, the depletion of NaHCO-extractable P (Olsen-P) extended about 1 cm into the outer compartment, but in the mycorrhizal plants a uniform P depletion zone extended up to 11.7 cm (the length of the hyphal compartment) from the root surface. In the outer compartment, the mycorrhizal hyphae length density was high (2.5–7 m cm soil) at the various distances (0–11.7 cm) from the root surface. Uptake rate of P by mycorrhizal hyphae was in the range of 3.3–4.3×10 mol s cm.
    Keywords: calcareous soil ; hyphal uptake ; phosphate ; VA-mycorrhiza ; white clover
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 10
    Language: English
    In: Plant and Soil, 2000, Vol.226(2), pp.275-285
    Description: New information on N uptake and transport of inorganic and organic N in arbuscular mycorrhizal fungi is reviewed here. Hyphae of the arbuscular mycorrhizal fungus Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (BEG 107) were shown to transport N supplied as 15 N-Gly to wheat plants after a 48 h labelling period in semi-hydroponic (Perlite), non-sterile, compartmentalised pot cultures. Of the 15 N supplied to hyphae in pot cultures over 48 h, 0.2 and 6% was transported to plants supplied with insufficient N or sufficient N, respectively. The increased 15 N uptake at the higher N supply was related to the higher hyphal length density at the higher N supply. These findings were supported by results from in vitro and monoxenic studies. Excised hyphae from four Glomus isolates (BEG 84, 107, 108 and 110) acquired N from both inorganic ( 15 NH 4 15 NO 3 , 15 NO 3 − or 15 NH 4 + ) and organic ( 15 N-Gly and 15 N-Glu, except in BEG 84 where amino acid uptake was not tested) sources in vitro during short-term experiments. Confirming these studies under sterile conditions where no bacterial mineralisation of organic N occurred, monoxenic cultures of Glomus intraradices Schenk and Smith were shown to transport N from organic sources ( 15 N-Gly and 15 N-Glu) to Ri T-DNA transformed, AM-colonised carrot roots in a long-term experiment. The higher N uptake (also from organic N) by isolates from nutrient poor sites (BEG 108 and 110) compared to that from a conventional agricultural field implied that ecotypic differences occur. Although the arbuscular mycorrhizal isolates used contributed to the acquisition of N from both inorganic and organic sources by the host plants/roots used, this was not enough to increase the N nutritional status of the mycorrhizal compared to non-mycorrhizal hosts.
    Keywords: arbuscular mycorrhiza ; Daucus carota ; Glomus mosseae ; Glomus intraradices ; monoxenic culture ; N uptake ; Triticum aestivum
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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