Most cited article - PubMed ID 33874214
The effect of magnesium ions on the vesicular-arbuscular mycorrhizal infection of maize roots
Inoculation with arbuscular mycorrhizal fungi (AMF) may improve plant performance at disturbed sites, but inoculation may also suppress root colonization by native AMF and decrease the diversity of the root-colonizing AMF community. This has been shown for the roots of directly inoculated plants, but little is known about the stability of inoculation effects, and to which degree the inoculant and the inoculation-induced changes in AMF community composition spread into newly emerging seedlings that were not in direct contact with the introduced propagules. We addressed this topic in a greenhouse experiment based on the soil and native AMF community of a post-mining site. Plants were cultivated in compartmented pots with substrate containing the native AMF community, where AMF extraradical mycelium radiating from directly inoculated plants was allowed to inoculate neighboring plants. The abundances of the inoculated isolate and of native AMF taxa were monitored in the roots of the directly inoculated plants and the neighboring plants by quantitative real-time PCR. As expected, inoculation suppressed root colonization of the directly inoculated plants by other AMF taxa of the native AMF community and also by native genotypes of the same species as used for inoculation. In the neighboring plants, high abundance of the inoculant and the suppression of native AMF were maintained. Thus, we demonstrate that inoculation effects on native AMF propagate into plants that were not in direct contact with the introduced inoculum, and are therefore likely to persist at the site of inoculation.
- MeSH
- Genotype MeSH
- Plant Roots microbiology MeSH
- Mycelium growth & development MeSH
- Mycorrhizae growth & development MeSH
- Soil MeSH
- Plants microbiology MeSH
- Seedlings microbiology MeSH
- Publication type
- Journal Article MeSH
- Names of Substances
- Soil MeSH
Considered to play an important role in plant mineral nutrition, arbuscular mycorrhizal (AM) symbiosis is a common relationship between the roots of a great majority of plant species and glomeromycotan fungi. Its effects on the plant host are highly context dependent, with the greatest benefits often observed in phosphorus (P)-limited environments. Mycorrhizal contribution to plant nitrogen (N) nutrition is probably less important under most conditions. Moreover, inasmuch as both plant and fungi require substantial quantities of N for their growth, competition for N could potentially reduce net mycorrhizal benefits to the plant under conditions of limited N supply. Further compounded by increased belowground carbon (C) drain, the mycorrhizal costs could outweigh the benefits under severe N limitation. Using a field AM fungal community or a laboratory culture of Rhizophagus irregularis as mycorrhizal inoculants, we tested the contribution of mycorrhizal symbiosis to the growth, C allocation, and mineral nutrition of Andropogon gerardii growing in a nutrient-poor substrate under variable N and P supplies. The plants unambiguously competed with the fungi for N when its supply was low, resulting in no or negative mycorrhizal growth and N-uptake responses under such conditions. The field AM fungal communities manifested their potential to improve plant P nutrition only upon N fertilization, whereas the R. irregularis slightly yet significantly increased P uptake of its plant host (but not the host's growth) even without N supply. Coincident with increasing levels of root colonization by the AM fungal structures, both inoculants invariably increased nutritional and growth benefits to the host with increasing N supply. This, in turn, resulted in relieving plant P deficiency, which was persistent in non-mycorrhizal plants across the entire range of nutrient supplies.
Large fraction of mineral nutrients in natural soil environments is recycled from complex and heterogeneously distributed organic sources. These sources are explored by both roots and associated mycorrhizal fungi. However, the mechanisms behind the responses of arbuscular mycorrhizal (AM) hyphal networks to soil organic patches of different qualities remain little understood. Therefore, we conducted a multiple-choice experiment examining hyphal responses to different soil patches within the root-free zone by two AM fungal species (Rhizophagus irregularis and Claroideoglomus claroideum) associated with Medicago truncatula, a legume forming nitrogen-fixing root nodules. Hyphal colonization of the patches was assessed microscopically and by quantitative real-time PCR (qPCR) using AM taxon-specific markers, and the prokaryotic and fungal communities in the patches (pooled per organic amendment treatment) were profiled by 454-amplicon sequencing. Specific qPCR markers were then designed and used to quantify the abundance of prokaryotic taxa showing the strongest correlation with the pattern of AM hyphal proliferation in the organic patches as per the 454-sequencing. The hyphal density of both AM fungi increased due to nitrogen (N)-containing organic amendments (i.e., chitin, DNA, albumin, and clover biomass), while no responses as compared to the non-amended soil patch were recorded for cellulose, phytate, or inorganic phosphate amendments. Abundances of several prokaryotes, including Nitrosospira sp. (an ammonium oxidizer) and an unknown prokaryote with affiliation to Acanthamoeba endosymbiont, which were frequently recorded in the 454-sequencing profiles, correlated positively with the hyphal responses of R. irregularis to the soil amendments. Strong correlation between abundance of these two prokaryotes and the hyphal responses to organic soil amendments by both AM fungi was then confirmed by qPCR analyses using all individual replicate patch samples. Further research is warranted to ascertain the causality of these correlations and particularly which direct roles (if any) do these prokaryotes play in the observed AM hyphal responses to organic N amendment, organic N utilization by the AM fungus and its (N-unlimited) host plant. Further, possible trophic dependencies between the different players in the AM hyphosphere needs to be elucidated upon decomposing the organic N sources.
Plant and fungal partners in arbuscular mycorrhizal symbiosis trade mineral nutrients for carbon, with the outcome of this relationship for plant growth and nutrition being highly context-dependent and changing with the availability of resources as well as with the specific requirements of the different partners. Here we studied how the model legume Medicago truncatula, inoculated or not with a mycorrhizal fungus Rhizophagus irregularis, responded to a gradient of light intensities applied over different periods of time, in terms of growth, phosphorus nutrition and the levels of root colonization by the mycorrhizal fungus. Short-term (6 d) shading, depending on its intensity, resulted in a rapid decline of phosphorus uptake to the shoots of mycorrhizal plants and simultaneous accumulation of phosphorus in the roots (most likely in the fungal tissues), as compared to the non-mycorrhizal controls. There was, however, no significant change in the levels of mycorrhizal colonization of roots due to short-term shading. Long-term (38 d) shading, depending on its intensity, provoked a multitude of plant compensatory mechanisms, which were further boosted by the mycorrhizal symbiosis. Mycorrhizal growth- and phosphorus uptake benefits, however, vanished at 10% of the full light intensity applied over a long-term. Levels of root colonization by the mycorrhizal fungus were significantly reduced by long-term shading. Our results indicate that even short periods of shade could have important consequences for the functioning of mycorrhizal symbiosis in terms of phosphorus transfer between the fungus and the plants, without any apparent changes in root colonization parameters or mycorrhizal growth response, and call for more focused research on temporal dynamics of mycorrhizal functioning under changing environmental conditions.
Communities of arbuscular mycorrhizal fungi (AMF) are crucial for promoting plant productivity in most terrestrial systems, including anthropogenically managed ecosystems. Application of AMF inocula has therefore become a widespread practice. It is, however, pertinent to understand the mechanisms that govern AMF community composition and their performance in order to design successful manipulations. Here we assess whether the composition and plant growth-promotional effects of a synthetic AMF community can be altered by inoculum additions of the isolates forming the community. This was determined by following the effects of three AMF isolates, each inoculated in two propagule densities into a preestablished AMF community. Fungal abundance in roots and plant growth were evaluated in three sequential harvests. We found a transient positive response in AMF abundance to the intraspecific inoculation only in the competitively weakest isolate. The other two isolates responded negatively to intra- and interspecific inoculations, and in some cases plant growth was also reduced. Our results suggest that increasing the AMF density may lead to increased competition among fungi and a trade-off with their ability to promote plant productivity. This is a key ecological aspect to consider when introducing AMF into soils.
- MeSH
- DNA, Fungal chemistry genetics MeSH
- Fungi classification genetics growth & development MeSH
- Plant Roots microbiology MeSH
- Molecular Sequence Data MeSH
- Mycorrhizae classification genetics growth & development MeSH
- Colony Count, Microbial MeSH
- Sequence Analysis, DNA MeSH
- Biota * MeSH
- Plant Development MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Names of Substances
- DNA, Fungal MeSH
The ability of arbuscular mycorrhizal (AM) fungi of different origin and cultivation history to tolerate excessive levels of manganese (Mn) was studied using hydroponic sand culture. Maize plants were colonised with two lineages of Glomus sp. BEG 140 from Mn-contaminated soil kept for 2 years in metal-free substrate or in the original soil. For comparison, the plants were also inoculated with Glomus intraradices BEG 75 from uncontaminated soil or were left uncolonised. Manganese stress was simulated by irrigation with nutrient solutions containing Mn at high concentrations (0.1, 0.5 and 1 mM); control plants were supplied with 3.8 microM Mn. Whereas the growth of maize plants was not suppressed by Mn at the concentrations examined, the development of AM fungi was negatively influenced by the higher Mn concentrations, with significant differences between isolates and cultivation lineages. The isolate Glomus sp. from Mn-contaminated soil showed higher tolerance to Mn than G. intraradices from uncontaminated soil. Colonisation by G. intraradices was reduced by almost 90% when irrigated with 1 mM Mn, whereas colonisation by the Glomus sp. lineage kept in contaminated soil still reached high levels (65% of the colonisation level of the control plants). The lineage of Glomus sp. cultured in inert metal-free substrate tolerated excessive Mn levels to a lesser extent than the lineage kept long-term in the original contaminated soil, but withstood Mn at higher concentrations than the G. intraradices from uncontaminated soil.
- MeSH
- Fungi metabolism MeSH
- Zea mays metabolism microbiology MeSH
- Soil Pollutants metabolism MeSH
- Manganese metabolism MeSH
- Mycorrhizae metabolism MeSH
- Symbiosis MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Names of Substances
- Soil Pollutants MeSH
- Manganese MeSH
The effect of 46 bacterial strains isolated from tilled and non-tilled soils collected at 3 localities on the growth of intraradical hyphae of the arbuscular mycorrhizal (AM) fungus Glomus claroideum was demonstrated. A larger number of stimulatory bacterial isolates was obtained from tilled soils, but the bacteria showing the strongest stimulation of hyphal growth were isolated from a soil that had not been cultivated. Isolates obtained from hyphae of AM fungi showed no substantial stimulatory effects, but produced more uniform effects on hyphal growth than the isolates of bacteria obtained from soil. Bacterial cenoses present in 3 different soils differ significantly in their effects on AM fungi.
Effects of two oligoamines, putrescine and spermine, on proliferation of intraradical hyphae in surface disinfected root segments were studied under axenic conditions in vitro. No significant effects of putrescine were observed. Spermine significantly stimulated hyphal growth at a concentration of about 1.5 mumol/L. High concentration (> 150 mumol/L) caused a strong inhibition of hyphal growth and of the percentage of root segments bearing proliferating hyphae. DL-alpha-difluoromethylornithine, a metabolic inhibitor of polyamine synthesis, caused a significant inhibition of proliferation of the hyphae only in the presence of 2 mumol/L spermine.
- MeSH
- Analysis of Variance MeSH
- Eflornithine pharmacology MeSH
- Fungi drug effects MeSH
- Plant Roots microbiology MeSH
- Zea mays microbiology MeSH
- Spermine pharmacology MeSH
- In Vitro Techniques MeSH
- Dose-Response Relationship, Drug MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Names of Substances
- Eflornithine MeSH
- Spermine MeSH
