Most cited article - PubMed ID 24611988
Soil and geography are more important determinants of indigenous arbuscular mycorrhizal communities than management practices in Swiss agricultural soils
Arbuscular mycorrhizal (AM) fungi are supposedly competing with ammonia-oxidizing microorganisms (AO) for soil nitrogen in form of ammonium. Despite a few studies directly addressing AM fungal and AO interactions, mostly in artificial cultivation substrates, it is not yet clear whether AM fungi can effectively suppress AO in field soils containing complex indigenous microbiomes. To fill this knowledge gap, we conducted compartmentalized pot experiments using four pairs of cropland and grassland soils with varying physicochemical properties. To exclude the interference of roots, a fine nylon mesh was used to separate the rhizosphere and mesh bags, with the latter being filled with unsterile field soils. Inoculation of plants with AM fungus Rhizophagus irregularis LPA9 suppressed AO bacteria (AOB) but not archaea (AOA) in the soils, indicating how soil nitrification could be suppressed by AM fungal presence/activity. In addition, in rhizosphere filled with artificial substrate, AM inoculation did suppress both AOB and AOA, implying more complex interactions between roots, AO, and AM fungi. Besides, we also observed that indigenous AM fungi contained in the field soils eventually did colonize the roots of plants behind the root barrier, and that the extent of such colonization was higher if the soil has previously been taken from cropland than from grassland. Despite this, the effect of experimental AM fungal inoculation on suppression of indigenous AOB in the unsterile field soils did not vanish. It seems that studying processes at a finer temporal scale, using larger buffer zones between rhizosphere and mesh bags, and/or detailed characterization of indigenous AM fungal and AO communities would be needed to uncover further details of the biotic interactions between the AM fungi and indigenous soil AO.
Phosphorus (P) acquisition is key for plant growth. Arbuscular mycorrhizal fungi (AMF) help plants acquire P from soil. Understanding which factors drive AMF-supported nutrient uptake is essential to develop more sustainable agroecosystems. Here we collected soils from 150 cereal fields and 60 non-cropped grassland sites across a 3,000 km trans-European gradient. In a greenhouse experiment, we tested the ability of AMF in these soils to forage for the radioisotope 33P from a hyphal compartment. AMF communities in grassland soils were much more efficient in acquiring 33P and transferred 64% more 33P to plants compared with AMF in cropland soils. Fungicide application best explained hyphal 33P transfer in cropland soils. The use of fungicides and subsequent decline in AMF richness in croplands reduced 33P uptake by 43%. Our results suggest that land-use intensity and fungicide use are major deterrents to the functioning and natural nutrient uptake capacity of AMF in agroecosystems.
- MeSH
- Mycorrhizae * MeSH
- Pesticides * MeSH
- Soil MeSH
- Soil Microbiology MeSH
- Plants microbiology MeSH
- Agriculture MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Names of Substances
- Pesticides * MeSH
- Soil MeSH
Arbuscular mycorrhizal fungi (AMF) represent important players in the structure and function of many ecosystems. Yet, we learn about their roles mostly from greenhouse-based experiments, with results subjected to cultivation bias. This study explores multiple aspects of this bias and separates the effect of increased nutrient availability from other cultivation specifics. For 15 grassland plant species from two functional groups (C3 grasses vs dicotyledonous forbs), we compared AMF communities of adults collected from non-manipulated vegetation with those in plants grown in a greenhouse. Nutrient availability was comparable to field conditions or experimentally elevated. We evaluated changes in AMF community composition, diversity, root colonisation, and the averages of functional traits characterising hyphal soil exploration. Additionally, we use the data from the greenhouse experiment to propose a new plant functional trait-the change of AMF colonisation in response to nutrient surplus. The AMF community differed profoundly between field-collected and greenhouse-grown plants, with a larger change of its composition in grass species, and AMF community composition in grasses also responded more to fertilisation than in forbs. Taxonomic and phylogenetic diversity declined more in forbs under cultivation (particularly with elevated nutrients), because in their roots, the AMF taxa from families other than Glomeraceae largely disappeared. A decline in AMF colonisation was not caused by greenhouse cultivation itself but selectively by the elevation of nutrient availability, particularly in grass host species. We demonstrate that the extent of decrease in AMF colonisation with elevated nutrients is a useful plant functional trait explaining an observed response of the plant community to manipulation.
- Keywords
- Arbuscular mycorrhizal fungi, Cultivation bias, Microscopy, Next-generation sequencing, Nutrient availability, Rhizophagus irregularis,
- MeSH
- Ecosystem MeSH
- Phylogeny MeSH
- Plant Roots MeSH
- Poaceae MeSH
- Mycobiome * MeSH
- Mycorrhizae * MeSH
- Soil MeSH
- Soil Microbiology MeSH
- Nutrients MeSH
- Publication type
- Journal Article MeSH
- Names of Substances
- Soil MeSH
Despite the crucial importance of arbuscular mycorrhizal fungi (AMF) for numerous processes within terrestrial ecosystems, knowledge of the determinants of AMF community structure still is limited, mainly because of the limited scope of the available individual case studies which often only include a few environmental variables. Here, we describe the AMF diversity of mid-European meadows (mown or regularly cut grasslands, or recently abandoned lands where grasslands established spontaneously) within a considerably heterogeneous landscape over a scale of several hundred kilometers with regard to macroclimatic, microclimatic, and soil parameters. We include data describing the habitat (including vegetation type), geography, and climate, and test their contribution to the structure of the AMF communities at a regional scale. We amplified and sequenced the ITS 2 region of the ribosomal DNA operon of the AMF from soil samples using nested PCR and Illumina pair-end amplicon sequencing. Habitat (especially soil pH) and geographical parameters (spatial distance, altitude, and longitude) were the main determinants of the structure of the AMF communities in the meadows at a regional scale, with the abundance of genera Septoglomus, Paraglomus, Archaeospora, Funneliformis, and Dominikia driving the main response. The effects of climate and vegetation type were not significant and were mainly encompassed within the geography and/or soil pH effects. This study illustrates how important it is to have a large set of environmental metadata to compare the importance of different factors influencing the AMF community structure at large spatial scales.
- Keywords
- 5.8S-ITS4 primers, Driving factor, Glomeromycotina, Illumina sequencing, Krüger fragment, Meadow,
- MeSH
- DNA, Fungal MeSH
- Ecosystem MeSH
- Mycobiome * MeSH
- Mycorrhizae * MeSH
- Grassland MeSH
- Soil MeSH
- Soil Microbiology MeSH
- Geography MeSH
- Publication type
- Journal Article MeSH
- Names of Substances
- DNA, Fungal MeSH
- Soil MeSH
Biochar has been heralded as a multipurpose soil amendment to sustainably increase soil fertility and crop yields, affect soil hydraulic properties, reduce nutrient losses, and sequester carbon. Some of the most spectacular results of biochar (and organic nutrient) inputs are the terra preta soils in the Amazon, dark anthropogenic soils with extremely high fertility sustained over centuries. Such soil improvements have been particularly difficult to achieve on a short run, leading to speculations that biochar may need to age (weather) in soil to show its best. Further, interaction of biochar with arbuscular mycorrhizal fungi (AMF), important root symbionts of a great majority of terrestrial plants including most agricultural crops, remains little explored. To study the effect of aged biochar on highly mycotrophic Andropogon gerardii plants and their associated AMF, we made use of softwood biochar, collected from a historic charcoal burning site. This biochar (either untreated or chemically activated, the latter serving as a proxy for freshly prepared biochar) was added into two agricultural soils (acid or alkaline), and compared to soils without biochar. These treatments were further crossed with inoculation with a synthetic AMF community to address possible interactions between biochar and the AMF. Biochar application was generally detrimental for growth and mineral nutrition of our experimental plants, but had no effect on the extent of their root colonized by the AMF, nor did it affect composition of their root-borne AMF communities. In contrast, biochar affected development of two out of five AMF (Claroideoglomus and Funneliformis) in the soil. Establishment of symbiosis with AMF largely mitigated biochar-induced suppression of plant growth and mineral nutrition, mainly by improving plant acquisition of phosphorus. Both mycorrhizal and non-mycorrhizal plants grew well in the acid soil without biochar application, whereas non-mycorrhizal plants remained stunted in the alkaline soils under all situations (with or without biochar). These different and strong effects indicate that response of plants to biochar application are largely dependent on soil matrix and also on microbes such as AMF, and call for further research to enable qualified predictions of the effects of different biochar applications on field-grown crops and soil processes.
- Keywords
- arbuscular mycorrhizal fungi, community, historic biochar, mycorrhizal response, nitrogen, phosphorus,
- Publication type
- Journal Article MeSH
Common mycorrhizal networks (CMNs) formed by arbuscular mycorrhizal fungi (AMF) interconnect plants of the same and/or different species, redistributing nutrients and draining carbon (C) from the different plant partners at different rates. Here, we conducted a plant co-existence (intercropping) experiment testing the role of AMF in resource sharing and exploitation by simplified plant communities composed of two congeneric grass species (Panicum spp.) with different photosynthetic metabolism types (C3 or C4). The grasses had spatially separated rooting zones, conjoined through a root-free (but AMF-accessible) zone added with 15N-labeled plant (clover) residues. The plants were grown under two different temperature regimes: high temperature (36/32°C day/night) or ambient temperature (25/21°C day/night) applied over 49 days after an initial period of 26 days at ambient temperature. We made use of the distinct C-isotopic composition of the two plant species sharing the same CMN (composed of a synthetic AMF community of five fungal genera) to estimate if the CMN was or was not fed preferentially under the specific environmental conditions by one or the other plant species. Using the C-isotopic composition of AMF-specific fatty acid (C16:1ω5) in roots and in the potting substrate harboring the extraradical AMF hyphae, we found that the C3-Panicum continued feeding the CMN at both temperatures with a significant and invariable share of C resources. This was surprising because the growth of the C3 plants was more susceptible to high temperature than that of the C4 plants and the C3-Panicum alone suppressed abundance of the AMF (particularly Funneliformis sp.) in its roots due to the elevated temperature. Moreover, elevated temperature induced a shift in competition for nitrogen between the two plant species in favor of the C4-Panicum, as demonstrated by significantly lower 15N yields of the C3-Panicum but higher 15N yields of the C4-Panicum at elevated as compared to ambient temperature. Although the development of CMN (particularly of the dominant Rhizophagus and Funneliformis spp.) was somewhat reduced under high temperature, plant P uptake benefits due to AMF inoculation remained well visible under both temperature regimes, though without imminent impact on plant biomass production that actually decreased due to inoculation with AMF.
After abandonment of agricultural fields, some grassland plant species colonize these sites with a frequency equivalent to dry grasslands (generalists) while others are missing or underrepresented in abandoned fields (specialists). We aimed to understand the inability of specialists to spread on abandoned fields by exploring whether performance of generalists and specialists depended on soil abiotic and/or biotic legacy. We performed a greenhouse experiment with 12 species, six specialists and six generalists. The plants were grown in sterile soil from dry grassland or abandoned field inoculated with microbial communities from one or the other site. Plant growth, abundance of mycorrhizal structures and plant response to inoculation were evaluated. We focused on arbuscular mycorrhizal fungi (AMF), one of the most important parts of soil communities affecting plant performance. The abandoned field soil negatively affected plant growth, but positively affected plant response to inoculation. The AMF community from both sites differed in infectivity and taxa frequencies. The lower AMF taxa frequency in the dry grassland soil suggested a lack of functional complementarity. Despite the fact that dry grassland AMF produced more arbuscules, the dry grassland inoculum did not improve phosphorus nutrition of specialists contrary to the abandoned field inoculum. Inoculum origin did not affect phosphorus nutrition of generalists. The lower effectiveness of the dry grassland microbial community toward plant performance excludes its inoculation in the abandoned field soil as a solution to allow settlement of specialists. Still, the distinct response of specialists and generalists to inoculation suggested that they differ in AMF responsiveness.
- Keywords
- Fungal structures, Mycorrhizal response, Native AMF, Soil biota, Soil legacy,
- MeSH
- Fungi MeSH
- Plant Roots MeSH
- Microbiota * MeSH
- Mycorrhizae * MeSH
- Grassland MeSH
- Soil MeSH
- Soil Microbiology MeSH
- Plant Development MeSH
- Publication type
- Journal Article MeSH
- Names of Substances
- Soil MeSH
Development of arbuscular mycorrhizal fungal colonization of roots and the surrounding soil is the central process of mycorrhizal symbiosis, important for ecosystem functioning and commercial inoculum applications. To improve mechanistic understanding of this highly spatially and temporarily dynamic process, we developed a three-dimensional model taking into account growth of the roots and hyphae. It is for the first time that infection within the root system is simulated dynamically and in a spatially resolved way. Comparison between data measured in a calibration experiment and simulated results showed a good fit. Our simulations showed that the position of the fungal inoculum affects the sensitivity of hyphal growth parameters. Variation in speed of secondary infection and hyphal lifetime had a different effect on root infection and hyphal length, respectively, depending on whether the inoculum was concentrated or dispersed. For other parameters (branching rate, distance between entry points), the relative effect was the same independent of inoculum placement. The model also indicated that maximum root colonization levels well below 100%, often observed experimentally, may be a result of differential spread of roots and hyphae, besides intrinsic plant control, particularly upon localized placement of inoculum and slow secondary infection.
Monitoring populations of arbuscular mycorrhizal fungi (AMF) in roots is a pre-requisite for improving our understanding of AMF ecology and functioning of the symbiosis in natural conditions. Among other approaches, quantification of fungal DNA in plant tissues by quantitative real-time PCR is one of the advanced techniques with a great potential to process large numbers of samples and to deliver truly quantitative information. Its application potential would greatly increase if the samples could be preserved by drying, but little is currently known about the feasibility and reliability of fungal DNA quantification from dry plant material. We addressed this question by comparing quantification results based on dry root material to those obtained from deep-frozen roots of Medicago truncatula colonized with Rhizophagus sp. The fungal DNA was well conserved in the dry root samples with overall fungal DNA levels in the extracts comparable with those determined in extracts of frozen roots. There was, however, no correlation between the quantitative data sets obtained from the two types of material, and data from dry roots were more variable. Based on these results, we recommend dry material for qualitative screenings but advocate using frozen root materials if precise quantification of fungal DNA is required.
- MeSH
- DNA, Fungal genetics isolation & purification MeSH
- Plant Roots chemistry growth & development microbiology MeSH
- Medicago truncatula chemistry growth & development microbiology MeSH
- Mycorrhizae chemistry genetics MeSH
- Preservation, Biological MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Names of Substances
- DNA, Fungal MeSH
