Differential benefits of arbuscular mycorrhizal and ectomycorrhizal infection of Salix repens

 The functional significance of arbuscular mycorrhiza (AM) and ectomycorrhiza (EcM) for Salix repens, a dual mycorrhizal plant, was investigated over three harvest periods (12, 20 and 30 weeks). Cuttings of S. repens were collected in December (low shoot P) and March (high shoot P). Glomus mosseae (an arbuscular mycorrhizal fungus, AMF) resulted in low AM colonization (<5%), but showed large short-term (<12 weeks) effects on shoot growth and root length. Hebeloma leucosarx (an ectomycorrhizal fungus, EcMF) resulted in high EcM colonization (70%), but benefits occurred over a longer term (>12 weeks). Furthermore, G. mosseae colonization resulted in higher shoot P uptake, shoot growth, root growth and response duration for S. repens collected in December than for those collected in March, whereas with H. leucosarx and the non-mycorrhizal treatment there were no differences between cuttings collected on different dates. Low AMF colonization was effective in the short term for cuttings at both collecting dates. Low AMF colonization of S. repens occurred irrespective of the amount of AMF inoculum used. The intensities and relative amounts of AMF structures in S. repens and Trifolium repens were compared over three harvest periods (12, 20 and 30 weeks) to assess plant species effects on AM colonization patterns. Accepted: 13 October 2000     

Differential host plant performance as a function of soil arbuscular mycorrhizal fungal communities: experimentally manipulating co-occurring Glomus species

In order to evaluate host plant performance relative to different soil arbuscular mycorrhizal fungal (AMF) communities, Andropogon gerardii seedlings were grown with nine different AMF communities. The communities consisted of 0, 10, or 20 spores of Glomus etunicatum and 0, 10, or 20 spores of Glomus intraradices in all possible combinations. Spores were produced by fungal cultures originating on A. gerardii in a serpentine plant community; seeds of A. gerardii were collected at the same site. The experiment was performed in the greenhouse using a mixture of sterilized serpentine soil and sand to which naturally occurring non-mycorrhizal microbes were added. There was no difference in root AMF colonization rates between single species communities of either G. etunicatum or G. intraradices, but G. intraradices enhanced plant growth and G. etunicatum did not. However, plants grew larger with some combinations of G.␣intraradices plus G. etunicatum than with the same quantity of G. intraradices alone. These results suggest the potential for niche complementarity in the mycorrhizal fungi. That G. etunicatum only increased plant growth in the presence of G. intraradices could be illustrative of why AMF that appear to be parasitic or benign when examined in isolation are maintained within multi-species mycorrhizal communities in nature.     

Arbuscular Mycorrhizal Fungi and Rhizospheric Bacteria Diversity Along an Altitudinal Gradient in South American Puna Grassland

Rhizospheric soil samples were taken from Puna native grasses along an altitudinal gradient. Biodiversity of arbuscular mycorrhizal fungi (AMF) and associated bacteria was analyzed considering altitude and grasses photosynthetic pathways (metabolic type C₃, C₄). Cultivation-dependent approaches were applied to obtain further information about the phylogeny of the dominating cultivable aerobic–heterotrophic bacteria communities present in rhizospheric soil samples. In average, the bacterial count ranged between 1.30 × 10² and 8.66 × 10⁴ CFU g⁻¹ of dry weight of soil. Individual bacterial colonies of aerobic heterotrophic bacteria grown on R2A medium were morphologically grouped and identified as typical soil bacteria belonging to the genera Bacillus, Pseudomonas, and Arthrobacter. Ten AMF taxa were found: Acaulospora sp., A. laevis, A. spinosa, Gigaspora sp., Gi. ramisporophora, Glomus sp., Gl. aggregatum, Gl. ambisporum, Gl. sinuosum, and Scutellospora biornata. AMF diversity decreased with altitude.     

西南桦幼苗接种丛枝菌根真菌的生长与光合生理响应

为了解丛枝菌根真菌(arbuscular mycorrhiza,AMF)对西南桦幼苗生长和光合生理的影响,对西南桦(Betula alnoides)优良无性系接种AMF菌株后的生长、光合参数、叶绿素含量和荧光参数进行了研究。结果表明,6个AMF菌株均能与西南桦无性系幼苗形成共生体,接种根内球囊霉(Glomus intraradices)菌株(AMF5)和摩西球囊霉(G.mosseae)HUN03B菌株(AMF3)显著提高了幼苗生长量、净光合速率、水分利用效率、叶绿素含量和荧光参数(P0.05),显示出AMF5、AMF3与幼苗的亲和力明显优于其他菌株。西南桦4个无性系间的菌根侵染率差异不显著(P0.05),但AMF对无性系FB4、BY1的促生效应显著优于FB4+和A5。因此,适合与西南桦共生的优良菌株为AMF5和AMF3,这为西南桦菌根化育苗提供理论依据。     

Arbuscular mycorrhizal propagules in soils from a tropical forest and an abandoned cornfield in Quintana Roo, Mexico: visual comparison of most-probable-number estimates

The present study was aimed at comparing the number of arbuscular mycorrhizal fungi (AMF) propagules found in soil from a mature tropical forest and that found in an abandoned cornfield in Noh-Bec Quintana Roo, Mexico, during three seasons. Agricultural practices can dramatically reduce the availability and viability of AMF propagules, and in this way delay the regeneration of tropical forests in abandoned agricultural areas. In addition, rainfall seasonality, which characterizes deciduous tropical forests, may strongly influence AMF propagules density. To compare AMF propagule numbers between sites and seasons (summer rainy, winter rainy and dry season), a “most probable number” (MPN) bioassay was conducted under greenhouse conditions employing Sorgum vulgare L. as host plant. Results showed an average value of 3.5 ± 0.41 propagules in 50 ml of soil for the mature forest while the abandoned cornfield had 15.4 ± 5.03 propagules in 50 ml of soil. Likelihood analysis showed no statistical differences in MPN of propagules between seasons within each site, or between sites, except for the summer rainy season for which soil from the abandoned cornfield had eight times as many propagules compared to soil from the mature forest site for this season. Propagules of arbuscular mycorrhizal fungi remained viable throughout the sampling seasons at both sites. Abandoned areas resulting from traditional slash and burn agriculture practices involving maize did not show a lower number of AMF propagules, which should allow the establishment of mycotrophic plants thus maintaining the AMF inoculum potential in these soils.     

Does the sequence of plant dominants affect mycorrhiza development in simulated succession on spoil banks?

The aim of this field study was to examine how the development of arbuscular mycorrhizal fungi (AMF) on coal mine spoil banks is affected by the presence of plants with different mycorrhizal status. A 3-year trial was conducted on the freshly created spoil bank Vršany, North-Bohemian coal basin, the Czech Republic. Three plant species – non-mycotrophic annual Atriplex sagittata, highly mycotrophic annual Tripleurospermum inodorum (both dominants of early stages of succession) and facultatively mycotrophic Arrhenatherum elatius (a perennial grass species of the later stage of succession) – were planted on 1 m² plots over 3 years in different sequences that simulated the progress of succession on spoil banks. The development of AMF populations was monitored by evaluation of mycorrhizal colonization of plant roots and by measurement of the mycorrhizal inoculation potential (MIP) of soil. These two parameters were compared between plots inoculated with the mixture of three AMF isolates – Glomus mosseae BEG95, G. claroideum BEG96 and G. intraradices BEG140 – (“inoculated plots”) and plots exposed only to natural dispersal of AMF propagules (“uninoculated plots”). Highly colonized roots of plants together with a high MIP of soil in uninoculated plots were already found at the end of the first season, indicating rapid natural dispersal of AMF propagules. Root colonization of facultatively mycotrophic and non-mycotrophic plants in later years was affected by the mycorrhizal status of the previous plant species. The MIP of soil continuously increased throughout the experiment; in uninoculated plots, the MIP was temporarily decreased if plant species of higher mycotrophy were replaced by species of lower mycotrophy. The results lead to the conclusion that AMF colonize freshly formed sites very quickly and reproduce or accumulate in the soil, which leads to increasing MIP values. However, this infective potential can be decreased if non-mycotrophic plants predominate on the site.     

Displacement of an herbaceous plant species community by mycorrhizal and non-mycorrhizal Gmelina arborea, an exotic tree, grown in a microcosm experiment

Gmelina arborea Roxb. (Gmelina, Yemane) is a fast growing tree, native from India and considered as a potentially invasive woody plant in West Africa. Mycorrhizal inoculation of seedlings with Glomus intraradices was performed to study (1) the effect on the growth of G. arborea, (2) the impact on the catabolic diversity of soil microbial communities and (3) the influence on the structure of herbaceous plant species communities in microcosms. Treatments consisted of control plants, pre-planting fertilizer application and arbuscular mycorrhizal (AM) inoculation. After 4 months’ culture in autoclaved soil, G. arborea seedlings were either harvested for growth measurement or transferred into containers filled with the same soil but not sterilized. Other containers were kept without G. arborea seedlings. After 12 months’ further culture, effects of fertilizer amendment and AM inoculation on the growth of G. arborea seedlings were recorded. AM colonization was significantly and positively correlated with plant diversity. The substrate-induced respiration response to carboxylic acids was significantly higher in the absence of G. arborea and in the presence of G. intraradices as compared to the other treatments. The influence of AM symbiosis on plant coexistence and on allelopathic processes of invasive plants are discussed.     

Interactions of arbuscular mycorrhizae,Meloidogyne arenaria,and phosphorus fertilization on peanut

 The individual and combined effects of two arbuscular mycorrhizal fungi (AMF), Meloidogyne arenaria, and phosphorus (P) fertilization, (0, 25, 75, and 125 μg/g soil) on peanut plant growth and pod yield were determined in greenhouse studies. Best growth and yield usually occurred at 75 or 125 μg P regardless of inoculation treatment. Peanut growth and yield were generally stimulated by AMF development, and growth alone was suppressed by M. arenaria at 0 and 25 μg P. In challenge inoculations, VAM increased peanut plant tolerance to the nematode and offset the growth reductions caused by M. arenaria at the two lower P levels. However, VAM and added P increased galling and M. arenaria egg production/g root, thereby increasing peanut susceptibility to nematode attack. M. arenaria had only a minimal effect on root colonization by AMF and sporulation by the fungi. Accepted: 9 June 1995     

Life history plasticity and fitness in a caddisfly in response to proximate cues of pond-drying

The majority of plants are involved in symbioses with arbuscular mycorrhizal fungi (AMF), and these associations are known to have a strong influence on the performance of both plants and insect herbivores. Little is known about the impact of AMF on complex trophic chains, although such effects are conceivable. In a greenhouse study we examined the effects of two AMF species, Glomus intraradices and G. mosseae on trophic interactions between the grass Phleum pratense, the aphid Rhopalosiphum padi, and the parasitic wasp Aphidius rhopalosiphi. Inoculation with AMF in our study system generally enhanced plant biomass (+5.2%) and decreased aphid population growth (−47%), but there were no fungal species-specific effects. When plants were infested with G. intraradices, the rate of parasitism in aphids increased by 140% relative to the G. mosseae and control treatment. When plants were associated with AMF, the developmental time of the parasitoids decreased by 4.3% and weight at eclosion increased by 23.8%. There were no clear effects of AMF on the concentration of nitrogen and phosphorus in plant foliage. Our study demonstrates that the effects of AMF go beyond a simple amelioration of the plants’ nutritional status and involve rather more complex species-specific cascading effects of AMF in the food chain that have a strong impact not only on the performance of plants but also on higher trophic levels, such as herbivores and parasitoids.     

Exogenous systemin has a contrasting effect on disease resistance in mycorrhizal tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis>) plants infected with necrotrophic or hemibiotrophic pathogens

A study was performed to determine the effect of the systemin polypeptide on the bio-protective effect of arbuscular mycorrhizal fungi (AMF) in tomato plants infected with Alternaria solani, Phytophthora infestans or P. parasitica. Before infection, tomato plants were colonized with two different AMF, Glomus fasciculatum or G. clarum. In addition, a group of inoculated plants was treated with systemin, just after emergence. The exogenous application of systemin marginally suppressed the resistance against A. solani leaf blight observed in G. fasciculatum mycorrhizal plants but significantly enhanced it in plants colonized with G. clarum. Systemin induced resistance to P. parasitica in leaves of G. fasciculatum mycorrhizal plants, in which AMF colonization alone was shown to have no protective effect. Conversely, none of the treatments led to resistance to root or stem rots caused by P. infestans or P. parasitica. The above effects did not correlate with changes in the activity levels of β-1,3-glucanase (BG), chitinase (CHI), peroxidase (PRX), and phenylalanine ammonium lyase (PAL) in leaves of infected plants. However, they corroborated previous reports showing that colonization by AMF can lead to a systemic resistance response against A. solani. Systemic resistance to A. solani was similarly observed in non-mycorrhizal systemin-treated plants, which, in contrast, showed increased susceptibility to P. infestans and P. parasitica. The results indicated that the pattern of systemic disease resistance conferred by mycorrhizal colonization was dependent on the AMF employed and could be altered by the exogenous application of systemin, by means of a still undefined mechanism.     

Dosage-dependent shift in the spore community of arbuscular mycorrhizal fungi following application of tannery sludge

The controlled disposal of tannery sludge in agricultural soils is a viable alternative for recycling such waste; however, the impact of this practice on the arbuscular mycorrhizal fungi (AMF) communities is not well understood. We studied the effects of low-chromium tannery sludge amendment in soils on AMF spore density, species richness and diversity, and root colonization levels. Sludge was applied at four doses to an agricultural field in Rolandia, Paraná state, Brazil. The sludge was left undisturbed on the soil surface and then the area was harrowed and planted with corn. The soil was sampled at four intervals and corn roots once within a year (2007/2008). AMF spore density was low (1 to 49 spores per 50 cm³ of soil) and decreased as doses of tannery sludge increased. AMF root colonization was high (64%) and unaffected by tannery sludge. Eighteen AMF species belonging to six genera (Acaulospora, Glomus, Gigaspora, Scutellospora, Paraglomus, and Ambispora) were recorded. At the sludge doses of 9.0 and 22.6 Mg ha⁻¹, we observed a decrease in AMF species richness and diversity, and changes in their relative frequencies. Hierarchical grouping analysis showed that adding tannery waste to the soil altered AMF spore community in relation to the control, modifying the mycorrhizal status of soil and selectively favoring the sporulation of certain species.     

Effects of arbuscular mycorrhizal fungi on seedling growth and development of two wetland plants, Bidens frondosa L., and Eclipta prostrata (L.) L., grown under three levels of water availability

To identify the importance of arbuscular mycorrhizal fungi (AMF) colonizing wetland seedlings following flooding, we assessed the effects of AMF on seedling establishment of two pioneer species, Bidens frondosa and Eclipta prostrata grown under three levels of water availability and ask: (1) Do inoculated seedlings differ in growth and development from non-inoculated plants? (2) Are the effects of inoculation and degree of colonization dependent on water availability? (3) Do plant responses to inoculation differ between two closely related species? Inoculation had no detectable effects on shoot height, or plant biomass but did affect biomass partitioning and root morphology in a species-specific manner. Shoot/root ratios were significantly lower in non-inoculated E. prostrata plants compared with inoculated plants (0.381 ± 0.066 vs. 0.683 ± 0.132). Root length and surface area were greater in non-inoculated E. prostrata (259.55 ± 33.78 cm vs. 194.64 ± 27.45 cm and 54.91 ± 7.628 cm² vs. 46.26 ± 6.8 cm², respectively). Inoculation had no detectable effect on B. frondosa root length, volume, or surface area. AMF associations formed at all levels of water availability. Hyphal, arbuscular, and vesicular colonization levels were greater in dry compared with intermediate and flooded treatments. Measures of mycorrhizal responsiveness were significantly depressed in E. prostrata compared with B. frondosa for total fresh weight (−0.3 ± 0.18 g vs. 0.06 ± 0.06 g), root length (−0.78 ± 0.28 cm vs.−0.11 ± 0.07 cm), root volume (−0.49 ± 0.22 cm³ vs. 0.06 ± 0.07 cm³), and surface area (−0.59 ± 0.23 cm² vs.−0.03 ± 0.08 cm²). Given the disparity in species response to AMF inoculation, events that alter AMF prevalence in wetlands could significantly alter plant community structure by directly affecting seedling growth and development.     

Growth response of lentil and wheat to Glomus clarum NT4 over a range of P levels in a Saskatchewan soil containing indigenous AM fungi

 The growth responses of lentil (Lens esculenta L. cv. Laird) and two wheat cultivars (Triticum aestivum L. cv. Laura and Neepawa) to Glomus clarum NT4 in soil containing indigenous arbuscular mycorrhizal fungi (AMF) and fertilized with phosphorus at different (0, 5, 10, 20 ppm) levels was studied in a growth chamber. Soil was inoculated with a monospecific culture of G. clarum NT4 to provide an inoculant:indigenous AMF ratio of ca. 1 : 100. The shoot and root growth, and AMF colonization levels of NT4-inoculated lentil were significantly (P≤0.05) greater than the appropriate control plants in the unfertilized soil at 48 days after planting (DAP). At 95 DAP, NT4 inoculation had significantly increased the shoot dry weight (P≤0.08) and AMF colonization (P≤0.05) of lentil plants receiving 5 mg P kg^–1 soil, whereas 20 mg P kg^–1 soil reduced the shoot growth of NT4-inoculated plants. The NT4 inoculant had no effect (P≤0.05) on shoot P content, but increased (P≤0.08) the P-use efficiency of lentil plants receiving 5 mg P kg^–1 soil. In contrast to the inoculant's effect on lentil, NT4 generally had no positive effect on any of the parameters assessed for wheat cv. Laura at any P level at 48 or 95 DAP. Similarly, there was no positive effect of NT4 on shoot or root growth, or AMF colonization of wheat cv. Neepawa plants at any P level at 48 DAP. However, NT4 inoculation increased the grain yield of Neepawa by 20% (P≤0.05) when fertilized with 20 mg P kg^–1 soil. This yield increase was associated with a significant (P≤0.05) reduction in root biomass and a significant (P≤0.05) increase in the grain P content of inoculated plants. Thus, NT4 appears to have a preference for the Neepawa cultivar. Our results show that lentil was more dependent on mycorrhizae than wheat and responded to an AMF inoculant even in soil containing high levels of indigenous AMF. It might, therefore, be possible to develop mixed inoculants containing rhizobia and AMF for field production of legumes. Accepted: 22 February 1997     

Increased allocation to external hyphae of arbuscular mycorrhizal fungi under CO2 enrichment

Prunella vulgaris was inoculated with different arbuscular mycorrhizal fungi (AMF) and grown at two concentrations of CO₂ (ambient, 350 μl l⁻¹, and elevated, 600 μl l⁻¹) to test whether a plants response to elevated CO₂ is dependent on the species of AMF colonizing the roots. Using compartments accessible only to AMF hyphae but not to roots, we also tested whether elevated CO₂ affects the growth of external AMF hyphae. Plant biomass was significantly greater at elevated than at ambient CO₂; the biomass of the root system, for example, increased by a factor of 2. The colonization of AMF inside the root remained constant, indicating that the total AMF inside the root system also increased by a factor of 2. The length of external AMF hyphae at elevated CO₂ was up to 5 times that at ambient CO₂, indicating that elevated CO₂ promoted allocation of AMF biomass to the external hyphae. The concentration and content of phosphorus in the stolons differed significantly between ambient and elevated CO₂ but this resulted in either an increase or a decrease, according to which AMF isolate occupied the roots. We hypothesized that an increase in external hyphal growth at elevated CO₂ would result in increased P acquistion by the plant. To test this we supplied phosphorus, in a compartment only accessible to AMF hyphae. Plants did not acquire more phosphorus at elevated CO₂ when phosphorus was added to this compartment. Large increases in AMF hyphal growth could, however, play a significant role in the movement of fixed carbon to the soil and increase soil aggregation. Received: 28 March 1998 / Accepted: 27 August 1998     

Diversity and infectivity of arbuscular mycorrhizal fungi in agricultural soils of the Sichuan Province of mainland China

Knowledge about the presence and diversity of arbuscular mycorrhizal fungi (AMF) in a specific area is an essential first step for utilizing these fungi in any application. The community composition of AMF in intensively managed agricultural soil in the Sichuan Province of southwest China currently is unknown. In one set of samples, AMF were trapped in pot cultures from 40 fields growing legumes in the Panxi region, southeast Sichuan. In a second set of samples, the MPN method with four-fold dilutions and maize as host was used to estimate infective propagules in soil from another 50 agricultural sites throughout the province. Soil types were heterogeneous and were classified as purple, yellow, paddy and red. Crops at each site were either maize, wheat or sweet orange. From this set of soil, AMF spores were also extracted and identified. Including all ninety soils, thirty glomeromycotan species in Glomus (20 species), Acaulospora (four species), Scutellospora (three species), Ambispora (one species), Archaeospora (one species) and Paraglomus (one species) were identified. Yellow, red and purple soils yielded similar numbers of AMF species, while AMF species diversity was clearly lower in paddy soil. In trap culture soils, the most frequent species were Glomus aggregatum or Glomus intraradices, Glomus claroideum and Glomus etunicatum. The species Acaulospora capsicula, Acaulospora delicata, G. aggregatum (or intraradices), G. claroideum, Glomus epigaeum, G. etunicatum, Glomus luteum, Glomus monosporum, Glomus mosseae and Glomus proliferum were successfully cultured as single-species pot cultures in Plantago lanceolata. The three most frequent species in field soils were G. mosseae, Glomus caledonium and Glomus constrictum. MPN values varied between 17 and 3334 propagules 100 g soil⁻¹ among the fifty field sites sampled. Regression analysis, including host&soil, log(P) and pH as explanatory variables explained 59% of the variation in log(MPN). The highest MPN estimates were found in purple soil cropped with maize and citrus, 324 and 278 propagules 100 g soil⁻¹, respectively. The lowest MPN value, 54 propagules 100 g soil⁻¹, was measured in wheat in purple and yellow soil. Despite intensive agricultural management that can include often repeated tillage, our examination of 90 agricultural sites revealed that soils of the Sichuan region have moderate to high numbers of infective AMF propagules as well as a high AMF species diversity. This opens possibilities for further studies and utilization of AMF in agriculture and horticulture in the Sichuan province, People’s Republic of China.     

Arbuscular mycorrhizal fungus enhances P acquisition of wheat (Triticum aestivum L.) in a sandy loam soil with long-term inorganic fertilization regime

The P efficiency, crop yield, and response of wheat to arbuscular mycorrhizal fungus (AMF) Glomus caledonium were tested in an experimental field with long-term (19 years) fertilizer management. The experiment included five fertilizer treatments: organic amendment (OA), half organic amendment plus half mineral fertilizer (1/2 OM), mineral fertilizer NPK, mineral fertilizer NK, and the control (without fertilization). AMF inoculation responsiveness (MIR) of wheat plants at acquiring P were estimated by comparing plants grown in unsterilized soil inoculated with G. caledonium and in untreated soil containing indigenous AMF. Without AMF inoculation, higher crop yields but lower colonization rates were observed in the NPK and two OA-inputted treatments, and NPK had significantly (P < 0.05) lower impacts on organic C and available P in soils and thereby P acquisition of wheat plants compared with OA and 1/2 OM. G. caledonium inoculation significantly (P < 0.05) increased colonization rates with the NPK and two P-deficient treatments but significantly (P < 0.05) increased vegetative biomass, crop yield, and P acquisition of wheat as well as soil alkaline phosphatase (ALP) activity, only with the NPK treatment. This gave an MIR of ca. 45% on total P acquisition of wheat plants. There were no other remarkable MIRs. It suggested that the MIR is determined by soil available P status, and rational combination of AMF with chemical NPK fertilizer can compensate for organic amendments by improving P-acquisition efficiency in arable soils.     

Genetic analysis of the interaction between <Emphasis Type="Italic">Allium</Emphasis> species and arbuscular mycorrhizal fungi

The response of Allium cepa, A. roylei, A. fistulosum, and the hybrid A. fistulosum × A. roylei to the arbuscular mycorrhizal fungus (AMF) Glomus intraradices was studied. The genetic basis for response to AMF was analyzed in a tri-hybrid A. cepa × (A. roylei × A. fistulosum) population. Plant response to mycorrhizal symbiosis was expressed as relative mycorrhizal responsiveness (R′) and absolute responsiveness (R). In addition, the average performance (AP) of genotypes under mycorrhizal and non-mycorrhizal conditions was determined. Experiments were executed in 2 years, and comprised clonally propagated plants of each genotype grown in sterile soil, inoculated with G. intraradices or non-inoculated. Results were significantly correlated between both years. Biomass of non-mycorrhizal and mycorrhizal plants was significantly positively correlated. R′ was negatively correlated with biomass of non-mycorrhizal plants and hence unsuitable as a breeding criterion. R and AP were positively correlated with biomass of mycorrhizal and non-mycorrhizal plants. QTLs contributing to mycorrhizal response were located on a linkage map of the A. roylei × A. fistulosum parental genotype. Two QTLs from A. roylei were detected on chromosomes 2 and 3 for R, AP, and biomass of mycorrhizal plants. A QTL from A. fistulosum was detected on linkage group 9 for AP (but not R), biomass of mycorrhizal and non-mycorrhizal plants, and the number of stem-borne roots. Co-segregating QTLs for plant biomass, R and AP indicate that selection for plant biomass also selects for enhanced R and AP. Moreover, our findings suggest that modern onion breeding did not select against the response to AMF, as was suggested before for other cultivated species. Positive correlation between high number of roots, biomass and large response to AMF in close relatives of onion opens prospects to combine these traits for the development of more robust onion cultivars.     

Lack of arbuscular mycorrhizal colonisation in tea (<Emphasis Type="Italic">Camellia sinensis</Emphasis> L.) plants cultivated in Northern Iran

Soil and roots associated with different tea clones and nearby weeds (Veronica sp., Setaria sp., Salvia sp., Senecio sp. and Tripogon sp.) were sampled for arbuscular mycorrhizal fungi (AMF) in the tea gardens of Northern Iran. Spores were searched for in the soil and AMF colonisation determined microscopically and fatty acid signatures in roots was determined. Root samples from mycorrhizal and non-mycorrhizal clover were used as positive and negative controls. AMF spores were abundant in the tea garden soils; the genera Glomus and Acaulospora dominated. Microscopic observations of stained tea roots showed no sign of AMF. To confirm this, the roots were analysed for fatty acid signature compounds. The average level of PLFA 16:1ω5 as signature molecule for AMF in tea roots was 2 nmol g⁻¹ dry root, while the NLFA 16:1ω5 was not detectable. In mycorrhizal and non-mycorrhizal clover roots, the PLFA 16:1ω5 was 141and 5.74 nmol g⁻¹ dry root, respectively. In roots of weeds in tea plantations, the amount of PLFA 16:1ω5 was in the range 4.9 to 31.1 nmol g⁻¹ dry root. Thus, there was no evidence for AMF association in tea roots and weeds are thought to be the source of the spores in the soils. Finally, no mycorrhizal colonisation was found when tea plant seedlings were inoculated with AMF in pot cultures.     

Laboratory experiments imply the conditionality of mycorrhizal benefits for Salix repens: role of pH and nitrogen to phosphorus ratios

Responses of one arbuscular mycorrhizal fungus (Glomus mosseae) and two ectomycorrhizal fungi (Hebeloma leucosarx, Paxillus involutus) to a range of substrate conditions were investigated in the laboratory. Non-mycorrhizal controls were also included. Substrate conditions included three levels of nitrogen – phosphorus ratios, ranging from N limitation to P limitation (N/P ratio 5.4, 16.2, 48.6), and three pH's, ranging from acidic to alkaline (pH 4, 5.5, 7), in a full factorial experiment. Plant parameters (carbon gain, N and P-content, root length) were significantly affected by fungus, soil pH and soil N/P, and their interactions. Mycorrhizal benefits by ectomycorrhizal fungi (EcMF) were generally larger than by the arbuscular mycorrhizal fungi (AMF), when assessed by above-ground parameters. Glomus mosseae, despite low colonization, had a much larger positive effect on root length than those EcMF. Hebeloma leucosarx and P. involutus were equally effective, despite differences in proportional colonization. Hebeloma leucosarx was able to expand niche width of S. repens towards alkaline conditions. Results are discussed in the framework of a dune successional gradient from young, calcareous, humus-poor towards old, acidic, humus-rich soils.     

Status of arbuscular mycorrhizal fungi (AMF) in the Sundarbans of India in relation to tidal inundation and chemical properties of soil

The arbuscular mycorrhizal status of fifteen mangroves and one mangrove associate was investigated from 27 sites of three inundation types namely, diurnal, usual springtide and summer springtide. Roots and rhizospheric soil samples were analysed for spore density, frequency of mycorrhizal colonization and some chemical characteristics of soil. Relative abundance, frequency and spore richness of AMF were assessed at each inundation type. All the plant species except Avicennia alba exhibited mycorrhizal colonization. The study demonstrated that mycorrhizal colonization and spore density were more influenced by host plant species than tidal inundation. Forty four AMF species belonging to six genera, namely Acaulospora, Entrophospora, Gigaspora, Glomus, Sclerocystis and Scutellospora, were recorded. Glomus mosseae exhibited highest frequency at all the inundation types; Glomus fistulosum, Sclerocystis coremioides and Glomus mosseae showed highest relative abundance at sites inundated by usual springtides, summer springtides and diurnal tides, respectively. Spore richness of AMF was of the order usual springtide > diurnal > summer springtide inundated sites. The mean spore richness was 3.27. Diurnally inundated sites had the lowest concentrations of salinity, available phosphorus, exchangeable potassium, sodium and magnesium. Statistical analyses indicated that mycorrhizal frequency and AMF spore richness were significantly negatively correlated to soil salinity. Spore richness was also significantly negatively correlated to available phosphorus. The soil parameters of the usual springtide inundated sites appeared to be favourable for the existence of maximum number of AMF. Glomus mosseae was the predominant species in terms of frequency in the soils of the Sundarbans.