红三叶草丛枝菌根对有机磷的吸收

The capacities of two arbuscular mycorrhizal (AM) fungi, Glomus mosseae and Glomus versderme, tomineralize added organic P were studied in a sterilized calcareous soil. Mycorrhizal (inoculated with either of the AM fungi) and non-mycorrhizal red clover (Trghlium pmtense L.) plants were grown for eight weeksin pots with upper root, central hyphal and lower soil compartments. The hyphal and soil compartmentsreceived either organic P (as Na-phytate) or inorganic P (as KH₂PO₄) at tbe rate of 50 mg P kg^-1. No P wasadded to the root compartments. Control pots received no added P. Yields were higher in mycorrhizal than innon-mycorrhizal clover. Mycorrhizal inoculation doubled shoot P concentration and more than doubled total P uptake of plaflts in P-amended soil, irrespective of the form of applied P. The mycorrhizal contributionto inorganic P uptake was 80% or 76% in plants inoculated with G. mosseae or G. verefforme, respectively. Corresponding values were 74% and 82% when Na-phytate was applied. In the root compartments of the mycorrhizal treatments, the proportion of root length infected, hyphal length density and phosphatase activity were all higher when organic P was applied than when inorganic P was added.     

Improved growth and Cu tolerance of Cu excess-stressed white clover after inoculation with arbuscular mycorrhizal fungi

The effects of arbuscular mycorrhizal (AM) fungus, Glomus intraradices, on growth and copper (Cu) tolerance of white clover (Trifolium repens) were investigated in soils with different Cu amounts. The AM inoculation increased plant biomass and the total or bound Cu concentrations in shoots and roots but decreased the total Cu in soils and the exchangeable Cu in shoots, roots and soils at all Cu levels. Mycorrhizal plants had higher levels of root phosphorus and shoot zinc (Zn) at lower Cu levels and more nitrogen and Zn in roots and potassium, calcium and magnesium in shoots and roots at all Cu addition levels. Additionally, AM inoculation enhanced urease, acid phosphatase and catalase activities in rhizosphere soils and mycorrhizal roots showed higher levels of peroxidase, catalase, proline and soluble sugar at all Cu addition levels. These results indicate that mycorrhizal white clover is potentially suitable for Cu phytoremediation based on greenhouse studies.     

Arbuscular mycorrhizal fungi are directly and indirectly affected by glyphosate application

Glyphosate is a systemic non-selective herbicide, the most widely used in the world. Alongside with its use in agricultural and forestry systems, this herbicide is used in grasslands in late summer with the aim of promoting winter species with the consequent increase in stocking rate. However, its effects on non-target organisms, such as arbuscular mycorrhizal fungi (AMF), are unclear. Arbuscular mycorrhizal fungi (AMF) colonize the root of more than 80% of terrestrial plants, improving their growth and survival, and therefore playing a key role in ecosystem structure and function. The aim of this work was to investigate the possible pathways through which glyphosate application affects AMF spores viability and root colonization in grassland communities. Our hypothesis is that glyphosate application can damage AMF directly (through contact with spores and external hyphae) or indirectly through the changes it generates on host plants. The experiment had a factorial array with three factors: (1) plant species, at two levels (Paspalum dilatatum and Lotus tenuis), (2) doses of glyphosate, at three levels (0 l ha⁻¹, 0.8 l ha⁻¹ and 3 l ha ⁻¹), and (3) application site, at two levels: soil (direct pathway) and plant foliage (indirect pathway). Spore viability was reduced even under the lowest glyphosate rate, but only when it was applied on the soil. Total root colonization for both species was similarly decreased when glyphosate was applied to plant foliage or on soil, with no difference between 0.8 and 3 l ha⁻¹. The number of arbuscules was 20% lower when glyphosate was applied on plant foliage, than when it was applied on the soil. Our findings illustrate that glyphosate application negatively affects AMF functionality in grasslands, due to different causes depending on the herbicide application site. While, under field conditions, the occurrence of direct and/or indirect pathways will depend on the plant cover at the time of glyphosate application, the consequences of this practice on the plant community structure will vary with the mycorrhizal dependence of the species composition regardless of the pathway involved.     

丛枝菌根根外菌丝对铵态氮和硝态氮吸收能力的比较

采用空气隔板分室法并结合15N标记技术,以玉米为宿主植物并接种Glomus mosseae和Glomus intraradices,比较了这两种真菌根外菌丝对铵态氮和硝态氮吸收传递能力的差异。结果表明,丛枝菌根根外菌丝吸收传递氮的能力因菌种和氮素形态而异。两种真菌根外菌丝吸收传递NH4+-N能力均高于NO3--N;G. intraradices根外菌丝吸收传递氮的能力高于G. mosseae,这可能与两种真菌根外菌丝生长量有关。     

Time-course of heavy metal uptake in maize and clover as affected by root density and different mycorrhizal inoculation regimes

A pot experiment was conducted to test the effect of three microbial regimes on the time course of heavy metal uptake in clover and maize from an industrially polluted soil. The three treatments included: (1) an intact flora of bacteria and fungi, including indigenous arbuscular mycorrhizal (AM) fungi together with soil microfauna; (2) the indigenous bacterial/fungal flora except AM fungi, reintroduced into sterilized soil; or (3) the same bacterial/fungal flora plus an AM fungus. For the final harvest, two pot sizes were included to assess the effect of root density. Plant uptake of P and heavy metals varied according to plant species, harvest time and soil treatment. For both plant species, shoot concentration of Zn, Cd and Cu decreased and Ni increased with plant age. Plants growing in sterilized soil with reintroduced AM fungi generally grew better, but contained higher concentrations of heavy metals than those colonized by indigenous AM fungi. Plants with mycorrhiza frequently contained more P, Zn, Cd, Cu and Pb in roots and shoots compared to nonmycorrhizal plants. Elevated root/shoot concentration ratios of P and metals indicate a sequestration of metal phosphates in mycorrhizal roots. Mycorrhizal performance was influenced by root density. At low root densities, metal concentrations in mycorrhizal plants were reduced, whereas it had no effect at high root densities when the entire soil volume was efficiently exploited by roots. We conclude that root density data are essential for interpretations of the influence of AM on metal uptake in plants.     

Uptake and metabolism of nitrate in mycorrhizal plants as affected by water availability and N concentration in soil

We compare the effect of arbuscular mycorrhizal (AM) colonization and PO₄^?3 fertilization on nitrate assimilation, plant growth and proline content in lettuce plants growing under well‐watered (?0.04 MPa) or drought (?0.17 MPa) conditions. We also tested how AM‐colonization and PO₄^?3 fertilization influenced N uptake (¹⁵N) and the percentage of N derived from the fertilizer (% NdfF) by plants under a concentration gradient of N in soil. Growth of mycorrhizal plants was comparable with that of P‐fertilized plants only under well‐watered conditions. Shoot nitrogen content, proline and nitrate reductase activity were greater in AM than in P‐fertilized plants under drought. The addition of 100 μg g^?1 P to the soil did not replace the AM effect under drought. Under well‐watered conditions, AM plants showed similar (at 3 mmol N), greater (at 6 mmol N) or lesser (at 9 mmol N) %NdfF than P‐fertilized plants. Comparing a control (without AM inoculation) to AM plants, differences in % NdfF ranged from 138% (3 mmol N) to 22.6% (6 mmol N) whereas no differences were found at 9 mmol N. In comparison with P fertilization, mycorrhizal effects on %NdfF were only evident at the lowest N levels, which indicated a regulatory mechanism for N uptake in AM plants affected by N availability in the soil. At the highest N level, P‐fertilized plants showed the greatest %NdfF. In conclusion, AM symbiosis is important for N acquisition and N fertilizer utilization but this beneficial mycorrhizal effect on N nutrition is reduced under large quantities of N fertilizer.     

Underground communication of root hormones by common mycorrhizal network between trifoliate orange and white clover

Common mycorrhizal network (CMN) links up several coexisting plant individuals via underground root communication for resource sharing, while it is not known whether phytohormones participate in such communication. A two-chambered rootbox separated through 37-μm mesh was used to establish the CMN by Diversispora spurca between trifoliate orange (TO) and white clover (WC). After 20 weeks of inoculation, the CMN was established, as evident from high mycorrhizal buildup under supplier (mycorrhizal inoculation) TO–target (non-mycorrhizal inoculation) WC association. This CMN was eventually responsible for the significant increase in plant biomass of these associated plants. CMN decreased root abscisic acid (ABA) level in supplier and target plants, but increased root indole-3-acetic acid (IAA) level in supplier plant alone. CMN mediated significantly higher gibberellins (GAs) and zeatin riboside (ZR) concentration in roots of target plant, leaving supplier plant unaffected. Root ZR was bidirectionally transferred through the CMN. A higher root methyl jasmonate (MeJA) concentration was observed in supplier WC–target TO or supplier TO–supplier WC association, indicating an unidirectional communication from WC to TO. It suggested that except IAA, GAs, brassinosteroid (BR), and ABA, root MeJA and ZR were apparently involved in the underground communication by CMN.     

Yield and chemical composition of red clover and ladino clover as affected by phosphorus and calcium

In Japan red clover and ladino clover are a popular forage. These clovers are adaptable to a wide range of soil conditions, and respond well to fertilization. They are often grown on relatively infertile soils with the aid of complete fertilizers.¹     

丛枝菌根真菌对万寿菊生长、吸镉及生理特性的影响

A pot experiment was carried out to study the effects of three arbuscular mycorrhizal fungi (AMF), including Glomus intraradices, Glomus constrictum and Glomus mosseae, on the growth, root colonization and Cd accumulation of marigold (Tagetes erecta L.) at Cd addition levels of 0, 5 and 50 mg kg-1 in soil. The physiological characteristics, such as chlorophyll content, soluble sugar content, soluble protein content and antioxidant enzyme activity, of Tagetes erecta L. were also investigated. The symbiotic relationship between the marigold plant and arbuscular mycorrhizal fungi was well established under Cd stress. The symbiotic relationship was reffected by the better physiobiochemical parameters of the marigold plants inoculated with the three AMF isolates where the colonization rates in the roots were between 34.3% and 88.8%. Compared with the non-inoculated marigold plants, the shoot and root biomass of the inoculated marigold plants increased by 15.2%- 47.5% and 47.8%-130.1%, respectively, and the Cd concentration and accumulation decreased. The chlorophyll and soluble sugar contents in the mycorrhizal marigold plants increased with Cd addition, indicating that AMF inoculation helped the marigold plants to grow by resisting Cd stress. The antioxidant enzymes reacted differently with the three AMF under Cd stress. For plants inoculated with G. constrictum and G. mosseae, the activities of superoxide dismutase (SOD) and catalase (CAT) increased with increasing Cd addition, but peroxidase (POD) activity decreased with increasing Cd addition. For plants inoculated with G. intraradices, three of the antioxidant enzyme activities were significantly decreased at high levels of Cd addition. Overall, the activities of the three antioxidant enzymes in the plants inoculated with AMF were higher than those of the plants without AMF inoculation under Cd stress. Our results support the view that antioxidant enzymes have a great influence on the biomass of plants, and AMF can improve the capability of reactive oxygen species (ROS) scavenging and reduce Cd concentration in plants to alleviate Tagetes erecta L. from Cd stress.     

Uptake of zinc by Brassica napus as affected by sulphur supply

Industrial crops provide a possibility for utilization of heavy metal polluted soils. Knowledge of the factors which affect metal uptake by crops is therefore essential in order to develop concepts for the management of such soils. In pot experiments the uptake of Zn by oilseed rape increased considerably with the Zn supply. The increase of Zn uptake was counteracted partly by S. This protective effect of S was, however, not related to Zn retention in the roots.     

Symbiosis of Trifolium subterraneum with mycorrhizal fungi and Rhizobium trifolii as affected by ammonium sulphate and nitrification inhibitors

The symbioses between Trifolium subterraneum, mycorrhizal fungi and Rhizohium are affected by (NH₄)₂SO₄ and by the nitrification inhibitors 2-chloro-6 (trichloromethyl) pyridine (N-Serve) and 2-trichloromethyl pyridine (2TMP). At 50 μg · g^?1 soil N-Serve and 2TMP had toxic effects on plant growth, measured as leaf expansion, root length and dry weight. Lower concentrations of N-Serve also produced some toxic symptoms. The addition of (NH₄)₂SO₄ to the soil at 2 and 6 m-equiv NH⁺₄ per pot, resulted in reduced root length and nodulation. Shoot dry weight was reduced at 6 m-equiv NH⁺₄ per pot. In the presence of (NH₄)₂SO₄ the toxic effects of the nitrification inhibitors on plant growth were less.Both nitrification inhibitors reduced development of mycorrhizal entry-points and extent of root colonization (% infection). Percentage infection of the root system was also reduced by (NH₄)₂SO₄. Development of nodules on the lateral roots was increased in the presence of N-Serve at 5 and 15 μ · g^?1. This effect, however, was accompanied by a marked reduction in N₂ase activity. Smaller increases in nodulation were apparent with 2TMP and were associated with variable N₂ase activity.     

Rhizodeposition of nitrogen by red clover,white clover and ryegrass leys

Correct assessment of the rhizodeposition of N in grassland is essential for the evaluation of biological N₂-fixation of legumes, for the total N balance of agro-ecosystems, and for the pre-cropping value of grasslands. Using a leaf-feeding technique by which plants were ¹⁵N labelled while growing in mezotrons in the field, the rhizodeposition of N by unfertilised red clover, white clover and perennial ryegrass growing in pure stands was shown to amount to 64, 71 and 9 g N m⁻², respectively, over two complete growing seasons. The corresponding values for red clover and white clover growing in mixtures with ryegrass were 89 and 32 g N m⁻², respectively. The rhizodeposited N compounds, including fine roots, constituted more than 80% of the total plant-derived N in the soil, and in all cases exceeded the amount of N present in stubble. In the mixtures of red clover–ryegrass and white clover–ryegrass and the pure stands of red clover, white clover and ryegrass, respectively, the rhizodeposition constituted a 1.05, 1.52, 1.26, 2.21 and 2.77 fold increase over the total N in the shoots harvested during the two production years. In pure stands and mixtures of clover, 84 and 92%, respectively, of this N derived from biological N₂ fixation. It is concluded that rhizodeposition provides a very substantial input of N to the legume-based grassland systems with great consequences for ecosystem N balance and turnover. Furthermore, the amount of atmospheric-derived N in the rhizodeposits may exceed that in the harvested shoots.     

Contribution of arbuscular mycorrhizal fungi to utilization of organic sources of phosphorus by red clover in a calcareous soil

A glasshouse pot experiment investigated the uptake by arbuscular mycorrhizal (AM) fungi associated with red clover of three organic sources of P added to a sterilized calcareous soil of low P availability. Each pot was separated into a central compartment for plant growth and two outer compartments for external mycelium using 30-μm nylon mesh to restrict the roots but allow hyphal penetration. Plants in the central compartments were inoculated with the AM fungus Glomus versiforme and uninoculated controls were included. Plants were harvested on three occasions: 5, 7 and 10 weeks after sowing. Application of each of the three organic P sources (lecithin, RNA and sodium phytate) or inorganic P (KH₂PO₄) at 50 mg P kg⁻¹ to the outer compartments of mycorrhizal and uninoculated pots increased the yield, P concentration and total P uptake of red clover compared with pots to which no P was applied, with no differences among P sources in non-mycorrhizal plants but differences observed in mycorrhizal plants both 7 and 10 weeks after sowing suggesting differences in availability of the four P sources to AM mycelium. The contribution of external mycelium to plant uptake of applied P increased with time. The three organic P sources made smaller contributions to plant P nutrition than KH₂PO₄ at the first and second harvests. At the third harvest, the contribution from KH₂PO₄ was 23%, while those from lecithin, RNA and sodium phytate were 23, 17 and 31%, respectively. This suggests that with the mediation of AM fungi, soil organic P sources can make a contribution to host plant P nutrition comparable to that of soluble orthophosphate.     

Growth of cassava cultivar TMS 30572 as affected by alley-cropping and mycorrhizal inoculation

The effect of inoculation with Glomus clarum, a vesicular-arbuscular mycorrhiza fungus, and alley-cropping on the growth of the cassava cultivar, TMS 30572, was investigated under field conditions in a low nutrient tropical soil. Cassava was grown either interplanted between two hedgerow tree species (alley-cropped) or sole-cropped. Sub-plots were either inoculated with G. clarum or were not inoculated. No effort was made to destroy the indigenous mycorrhizal fungi. Three months after planting, no significant influence of G. clarum inoculation was observed on the growth of roots, shoots or leaf area index (LAI). However, with time, inoculation and system of cropping enhanced these growth parameters. Nine months after planting, the total biomass of alley-cropped cassava was significantly higher than that of inoculated and non-inoculated sole-cropped cassava. Inoculation had led to an increase in the fresh tuber yield of both the alley- and sole-cropped cassava 12 months after planting. The LAI of both alley- and sole-cropped cassava inoculated with G. clarum increased. Received: 6 December 1996     

Uptake of Cu2+ by starch granules as affected by counterions

Potato and wheat starch granules were soaked in 1% aqueous solutions of copper(II) salts: acetate, chloride, and sulfate. Such treatment caused sorption of Cu(2+) ions at the granule surface and their penetration into the granule interior as was proven, for sectioned granules of investigated starch, by scanning electron microscopy combined with an X-ray microanalysis system (energy dispersive spectroscopy). Copper ions incorporated into the granules influenced the starch thermal stability. Uptake of Cu(2+) by potato, determined by flame atomic absorption spectrometry, was much higher than obtained for the wheat starch. Moreover, it was dependent on copper counteranions present in the solution. In all investigated granules, the most effective sorption occurred in the acetate solution. Starch dehydration or/and freezing and thawing, affecting the water-dependent inner structure of the granules, also influenced the amount of Cu(2+) taken from the solutions. Thus, compared to that in native starch, this value was considerably higher in Cu(CH 3COO)2, almost unchanged in CuSO4, and significantly lower in the case of CuCl2 solution. The influence of chloride and sulfate anions seemed to correlate with their water structure-making and structure-breaking ability, affecting the migration of Cu(2+) in the amorphous parts of the granules. However, high Cu uptake observed for acetate solution could be explained on the basis of acetate anion hydrolysis activating the polysaccharide matrix for cation binding. The obtained results provide new information about interactions of starch granules with salt solution and therefore support our understanding of starch properties.     

Inter- and intraspecific functional variability of tropical arbuscular mycorrhizal fungi isolates colonizing corn plants

For a single plant species under the same environmental conditions, the interaction with arbuscular mycorrhizal fungi (AMF) and their contribution to plant growth varies among AMF isolates, with both inter and intraspecific variability. The present study evaluated the functional variability of 41 isolates of 20 species and eight genera of AMF for root colonization, growth promotion, and P uptake of corn and observed the relationship of this functional variability with the isolates genetic variability revealed by PCR-RFLP analysis. All the isolates abundantly colonized the corn roots, but only 23 promoted higher shoot dry mass and P leaf content. The cluster analysis based on functional variability data separated the isolates Acaulospora morrowiae (Am2), Acaulospora sp. (Aca), A. colombiana (Ac3, Ac4, and Ac5), Gigaspora albida (Gia1), Gi. margarita (Gim4 and Gim5), Gi. rosea (Gir), Rhizophagus clarus (Rc2, Rc3, Rc4, Rc5, and Rc6), Claroideoglomus etunicatum (Ce4), R. manihotis (Rm), Scutellospora calospora (Sc), S. heterogama (Sh2, Sh3, Sh4, and Sh5) and S. pellucida (Sp3) from the others at the distance of 80% functional similarity. These were considered efficient in promoting functional symbiosis in corn while the other isolates were considered inefficient. The cluster analysis obtained by the PCR-RFLP technique was partly coherent with the species classification based on spore morphology. The isolates of R. clarus fell into one cluster and the isolates of the Gigaspora and Scutellospora genera (Gigasporaceae family) were clustered in a second cluster, without the ability to separate the species of these genera.     

Potassium absorption and partitioning in cotton as affected by periods of potassium deficiency

Cotton (Gossypium hirsutum var. Latifolium) was grown in nutrient media, at two K levels: 58.5 mg/K and 11.7 mg/K. Potassium deficiency (11.7 mg K/g of K) was imposed upon cotton plants at different stages of plant development. A sequence of increasing sensitivity to K deficiency among cotton plant parts was observed: leaves<bolls<roots<stems. When K deficiency symptoms are clearly visible in the leaves, all the other plant parts are already affected. Bolls are a very important component in K partitioning within the cotton plant, but K is required most by the bur itself and is not translocated to seeds or fibers. Cotton could overcome a 30 day deficiency late in the season without significant losses in lint and seed cotton yields.     

Phosphorus uptake and growth of barley as affected by soil temperature and mycorrhizal infection

A glasshouse study was conducted to investigate the effects of soil temperatures of 20, 15 and 10°C on growth and phosphorus (P) uptake of barley (Hordeum vulgare L. cv. Galleon) inoculated with Glomus intraradices Schenck & Smith. Vesicular‐arbuscular (VA) mycorrhiza formation was significantly reduced as the soil temperature decreased. Plant growth depression due to temperature stress was more pronounced in mycorrhizal plants than in non‐mycorrhizal plants. The lower the soil temperature, the higher was the root‐shoot ratio. The ratio was also higher in non‐mycorrhizal plants than in mycorrhizal plants. Concentration of P in roots was influenced by mycorrhiza. Significant interaction between mycorrhiza and soil temperature was observed for root dry matter and specific P uptake (P uptake per unit weight of root). Compared to non‐mycorrhizal plants, specific P uptake in mycorrhizal plants was higher.     

Nodule numbers,colonization rates,and carbon accumulations of white clover response of nitrogen and phosphorus starvation in the dual symbionts of rhizobial and arbuscular mycorrhizal fungi

Leguminous plants can be dual colonized by rhizobia (Rh) and arbuscular mycorrhizal fungi (AMF). To test the affections of nodulation, colonization of AMF (AMF%) and the growth responses of white clover under crossed low nitrogen (N) and phosphorus (P) fertilization levels. The results showed that the nodule numbers were much more dense, significantly increased by AMF symbiosis, negatively controlled by the N levels but had no effect due to P levels. The influence of nodule numbers via AMF % was beyond P availability. The AMF% was related and favored with the better N and P nutrition, which may have better photosynthetic carbon (C) availability. The plant growth and C accumulation were significantly increased via rhizobium inoculation but were negatively affected by the AMF. The AMF colonization beyond P fertilization had strong effects on nodulation. Compared with rhizobium symbiosis, the AMF colonization requires a more C-composition between these two tertiary symbioses.     

Herbivory of an invasive slug in a model grassland community can be affected by earthworms and mycorrhizal fungi

Invasion of non-native species is among the top threats for the biodiversity and functioning of native and agricultural ecosystems worldwide. We investigated whether the herbivory of the slug Arion vulgaris (formerly Arion lusitanicus; Gastropoda), that is listed among the 100 worst alien species in Europe, is affected by soil organisms commonly present in terrestrial ecosystems (i.e. earthworms—Annelida: Lumbricidae and arbuscular mycorrhizal fungi—AMF, Glomerales). We hypothesized that slug herbivory would be affected by soil organisms via altered plant nutrient availability and plant quality. In a greenhouse experiment, we created a simple plant community consisting of a grass, a forb, and a legume species and inoculated these systems with either two earthworm species and/or four AMF taxa. Slugs were introduced after plants were established. Earthworms significantly reduced total slug herbivory in AMF-inoculated plant communities (P?=?0.013). Across plant species, earthworms increased leaf total N and secondary metabolites, AMF decreased leaf thickness. Mycorrhizae induced a shift in slug feeding preference from non-legumes to legumes; the grass was generally avoided by slugs. AMF effects on legume herbivory can partly be explained by the AMF-induced increase in total N and decrease in C/N ratio; earthworm effects are less clear as no worm-induced alterations of legume plant chemistry were observed. The presence of earthworms increased average AMF colonization of plant roots by 140 % (P?<?0.001). Total shoot mass was significantly increased by AMF (P?<?0.001). These data suggest that the feeding behavior of this invasive slug is altered by a belowground control of plant chemical quality and community structure.