Can intra‐specific genetic variation in arbuscular mycorrhizal fungi (Glomus etunicatum) affect a mesophyll‐feeding herbivore (Tupiocoris notatus Distant)?

Abstract.  1. Arbuscular mycorrhizal fungal (AMF) infection can have negative, positive or neutral effects on insect herbivore populations, but patterns are difficult to predict.
2. Intra-specific genetic variation in nutrient uptake ability between fungal isolates may also have indirect effects on insect herbivores due to changes in plant quality. In preliminary studies mirid ( Tupiocoris notatus ) populations were significantly reduced on tobacco ( Nicotiana rustica ) colonised by AMF but it was unknown if same-species fungal isolates differed in their effect.
3. An experiment was performed as a first test of the effect of intra-specific genetic variation in the mycorrhizal fungus Glomus etunicatum on mirid nymphal population structure, dynamics, and growth rate.
4. Mirid nymphal populations were lower on mycorrhizal fungal-infected plants. Population size, however, did not differ between the mycorrhizal isolates. While no statistical difference in population between isolates was found, one isolate consistently had 1.7–2.4 times lower mirid populations compared with the controls, indicating that the magnitude of effect is different between mycorrhizal isolates.
5. The significantly negative effect of AMF on mirid populations likely resulted from AMF-induced changes in plant quality (e.g. increased defence). This study lends further support to recent demonstrations that below-ground symbionts significantly influence above-ground processes. In addition, mycorrhizal fungi can affect insect population structure, which may have consequences for future herbivory.     

Arbuscular mycorrhizal symbiosis can counterbalance the negative influence of the exotic tree species Eucalyptus camaldulensis on the structure and functioning of soil microbial communities in a sahelian soil

The hypothesis of the present study was that bacterial communities would differentiate under Eucalyptus camaldulensis and that an enhancement of arbuscular mycorrhizal (AM) density would minimize this exotic plant species effect. Treatments consisted of control plants, preplanting fertilizer application and AM inoculation. After 4 months of culture in autoclaved soil, E. camaldulensis seedlings were either harvested for growth measurement or transferred into containers filled with the same soil but not sterilized. Other containers were kept without E. camaldulensis seedlings. After 12 months, effects of fertilizer amendment and AM inoculation were measured on the growth of Eucalyptus seedlings and on soil microbial communities. The results clearly show that this plant species significantly modified the soil bacterial community. Both community structure (assessed by denaturing gradient gel electrophoresis profiles) and function (assessed by substrate-induced respiration responses including soil catabolic evenness) were significantly affected. Such changes in the bacterial structure and function were accompanied by disturbances in the composition of the herbaceous plant species layer. These results highlight the role of AM symbiosis in the processes involved in soil bio-functioning and plant coexistence and in afforestation programmes with exotic tree species that target preservation of native plant diversity.     

Attenuation of cadmium toxicity in mycorrhizal celery (<Emphasis Type="Italic">Apium graveolens</Emphasis> L.)

A pot-culture experiment was carried out to investigate the effect of arbuscular mycorrhizal (AM) fungus (Glomus macrocarpum Tul. and Tul.) on plant growth and Cd²⁺uptake by Apium graveolens L. in soil with different levels of Cd²⁺. Mycorrhizal (M) and non-mycorrhizal (NM) plants were grown in soil with 0, 5, 10, 40 and 80 Cd²⁺ mg kg⁻¹soil. The infectivity of the fungus was not affected by the presence of Cd²⁺ in the soil. M plants showed better growth and less Cd²⁺ toxicity symptoms. Cd²⁺ root : shoot ratio was higher in M plants than in NM plants. These differences were more evident at highest Cd²⁺ level (80 mg kg⁻¹ soil). Chlorophyll a and chlorophyll b concentrations were significantly higher in AM-inoculated celery leaves. The dilution effect due to increased biomass, immobilization of Cd²⁺ in root and enhanced P-uptake in M plants may be related to attenuation of Cd²⁺toxicity in celery.     

Mycorrhiza influences plant community structure in succession on spoil banks

The experiment simulated a plant succession stage when perennial grasses (e.g. Calamagrostis epigejos) invade communities of annuals with different mycotrophy (e.g. Atriplex sagittata and Tripleurospermum inodorum) on coalmine spoil banks. Communities of these three model species were planted in 30 l microcosms either in the presence of pre-established mycelium network of three arbuscular mycorrhizal fungi (AMF) species (individually and in a mixture) or without AMF. Different AMF species had significantly different effects on individual plant species’ growth, which resulted in changes in plant community structure. While in the no-AMF treatment the non-mycotrophic plant species A. sagittata contributed nearly 70% to the total plant biomass, in the presence of the 3 AMF mixture the contribution of this species was only about 10%. Different effects of AMF on tiller formation by C. epigejos suggest that some AMF could have greater potential to promote the replacement of annuals by perennial grasses than others. It can be concluded that not merely the presence but also the identity of AMF present on spoil banks can affect the coexistence of plant dominants, the community structure and the progress of plant succession.     

The liverwort Marchantia foliacea forms a specialized symbiosis with arbuscular mycorrhizal fungi in the genus Glomus

Microscopic evidence suggests that fungi forming endosymbioses with liverworts in the Marchantiales are arbuscular mycorrhizal (AM) fungi from the Glomeromycota. Polymerase chain reaction amplification of ribosomal sequences confirmed that endophytes of the New Zealand liverwort, Marchantia foliacea, were members of the genus Glomus. Endophytes from two Glomus rDNA phylotypes were repeatedly isolated from geographically separated liverwort samples. Multiple phylotypes were present in the same liverwort patch. The colonizing Glomus species exhibited substantial internal transcribed spacer sequence variation within phylotypes. This work suggests that certain liverwort species may serve as a model for studying DNA sequence variation in colonizing AM phylotypes and specificity in AM-host relationships.     

Phosphorus nutrition-mediated effects of arbuscular mycorrhiza on leaf morphology and carbon allocation in perennial ryegrass

The aim of this work was to disentangle phosphorus status-dependent and -independent effects of arbuscular mycorrhizal fungus (AMF) on leaf morphology and carbon allocation in perennial ryegrass (Lolium perenne). To this end, we assessed the P-response function of morphological components in mycorrhizal and nonmycorrhizal plants of similar size. AMF (Glomus hoi) stimulated relative P-uptake rate, decreased leaf mass per area (LMA), and increased shoot mass ratio at low P supply. Lower LMA was caused by both decreased tissue density and thickness. Variation in tissue density was almost entirely caused by variations in soluble C, while that in thickness involved structural changes. All effects of AMF were indistinguishable from those mediated by increases in relative P-uptake rate through higher P-supply rates. Thus the relationships between relative P-uptake rate, leaf morphology and C allocation were identical in mycorrhizal and nonmycorrhizal plants. No evidence was found for AMF effects not mediated by changes in plant P status.     

Clonal diversity and population genetic structure of arbuscular mycorrhizal fungi (Glomus spp.) studied by multilocus genotyping of single spores

A nested multiplex PCR (polymerase chain reaction) approach was used for multilocus genotyping of arbuscular mycorrhizal fungal populations. This method allowed us to amplify multiple loci from Glomus single spores in a single PCR amplification. Variable introns in the two protein coding genes GmFOX2 and GmTOR2 were applied as codominant genetic markers together with the LSU rDNA. Genetic structure of Glomus spp. populations from an organically and a conventionally cultured field were compared by hierarchical sampling of spores from four plots in each field. Multilocus genotypes were characterized by SSCP (single stranded conformation polymorphism) and sequencing. All spore genotypes were unique suggesting that no recombination was taking place in the populations. There were no overall differences in the distribution of genotypes in the two fields and identical genotypes could be sampled from both fields. Analysis of gene diversity indicated that Glomus populations are subdivided between plots within each field. There were however, no subdivision between the fields.