Occurrence of non-mycorrhizal plant species in south Swedish rocky habitats is related to exchangeable soil phosphate

1 Plant species that do not typically form mycorrhiza are most likely to be successful under conditions where mycorrhizal fungi are not important for plant coexistence or where the costs of symbiosis outweigh the benefits. The relative occurrence of non-mycorrhizal species was investigated in relationship to exchangeable soil P in herbaceous vegetation, where arbuscular mycorrhizal (AM) associations are generally common. We investigated a total of 439 sites in rocky habitats with sparse vegetation and 110 meadows with dense vegetation. 2 In both rocky habitats and meadows, soil pH was inversely related to exchangeable P. In rocky habitats plant species richness increased greatly between pH 3 and 5 and was also inversely related to P. 3 Plant communities in rocky habitats contained a relatively larger proportion of non-mycorrhizal species than those in meadows. More non-mycorrhizal species occurred at high soil P in the rocky habitats, but no such relation was found in meadows. 4 Non-mycorrhizal species in rocky habitats were most common at low soil pH (high P availability). Plant species that thrived at extreme soil pH were often non-mycorrhizal. 5 The occurrence of fewer non-mycorrhizal plants in meadows than in rocky habitats supports the hypothesis that AM associations are more important in ecosystems with intense competition among plants. In rocky habitats, where abiotic stress may restrict photosynthesis more than nutrient limitation does, it is adaptive for plant species to utilize strategies other than mycorrhiza, particularly at low pH sites where P availability is likely to be adequate

Responses of arbuscular mycorrhizal fungi to long-term inorganic and organic nutrient addition in a lowland tropical forest

Improved understanding of the nutritional ecology of arbuscular mycorrhizal (AM) fungi is important in understanding how tropical forests maintain high productivity on low-fertility soils. Relatively little is known about how AM fungi will respond to changes in nutrient inputs in tropical forests, which hampers our ability to assess how forest productivity will be influenced by anthropogenic change. Here we assessed the influence of long-term inorganic and organic nutrient additions and nutrient depletion on AM fungi, using two adjacent experiments in a lowland tropical forest in Panama. We characterised AM fungal communities in soil and roots using 454-pyrosequencing, and quantified AM fungal abundance using microscopy and a lipid biomarker. Phosphorus and nitrogen addition reduced the abundance of AM fungi to a similar extent, but affected community composition in different ways. Nutrient depletion (removal of leaf litter) had a pronounced effect on AM fungal community composition, affecting nearly as many OTUs as phosphorus addition. The addition of nutrients in organic form (leaf litter) had little effect on any AM fungal parameter. Soil AM fungal communities responded more strongly to changes in nutrient availability than communities in roots. This suggests that the 'dual niches' of AM fungi in soil versus roots are structured to different degrees by abiotic environmental filters, and biotic filters imposed by the plant host. Our findings indicate that AM fungal communities are fine-tuned to nutrient regimes, and support future studies aiming to link AM fungal community dynamics with ecosystem function

The external mycorrhizal mycelium - growth and interactions with saprophytic microorganisms

The interactions between external mycorrhizal mycelia and saprophytic microorganisms were studied in experiments with growth chambers specially designed to enable the mycelia to develop in root-free soil compartments. The growth of the mycorrhizal mycelia was estimated by use of biochemical signature compounds. It was shown possible to estimate the biomass of the external mycelium of different arbuscular mycorrhizal fungi by use of the signature fatty acid 16:1w5 in soil and sand. The amount of this fatty acid was estimated as indicator both of phospholipids (PLFAs) and neutral lipids (NLFAs). The results indicated that PLFAs reflect mycelium on the AM fungi and NLFAs storage structures.No effects of the AM mycelium on the bacterial community were recorded in an agricultural soil, even though the AM mycelium constituted a large part of the biomass. In a study involving calcareous dune sand, the growth on the external AM mycelium decreased the amount of PLFA 18:2w6,9, indicating negative effects on growth of saprophytic fungi. Ectomycorrhizal mycelia of six different species reduced bacterial activity, estimated as thymidine incorporation, in experiments with a sandy soil. In these experiments no negative effect on bacterial biomass was observed. In a study on pines growing for eight months in a peat/sand mixture, both bacterial activity and biomass were lowered due to mycorrhizal inoculation. However, in the soils to which primary minerals as apatite and biotite had been added, the growth of Suillus variegatus increased bacterial activity. This demonstrated that, under certain, circumstances, ectomycorrhizal fungi may contribute to a significant carbon input to the soil which stimulates bacterial growth

Soil and plants in the sand steppe

Sand steppe is a rare vegetation type on sandy soils in southeastern Sweden with Koeleria glauca and Dianthus arenarius as the most characteristic plant species. The sand steppe areas ill eastern Skane were surveyed during 2004 and 2005. The vegetation composition was monitored and related to die pH and lime content Many sand steppes are close to acidification as indicated by low lime content ill die topsoil. However, places that were subjected to soil pertubation during die last 100 years still have high lime content in the topsoil. In addition to a high pH, repeated vegetation disturbance are needed to maintain die steppe vegetation. It Was found that sand steppe could best be restored ill sonic areas by bringing lime rich sand to the surface, and ill some areas by increasing the vegetation disturbance. The situation for die main sand steppe areas is discussed

Colonization by arbuscular mycorrhizal and fine endophytic fungi in herbaceous vegetation in the Canadian High Arctic

The occurrence of arbuscular mycorrhizal (AM) fungi was surveyed along a latitudinal gradient in Arctic Canada including Banks Island (73degreesN), Devon Island (74degreesN), Ellesmere Island (76degreesN), and the Magnetic North Pole at Ellef Ringnes Island (78degreesN). At Banks Island, AM fungi were present and colonized at a high intensity in all specimens of Potentilla hookeriana Lehm. - Potentilla pulchella R.Br., Arnica angustifolia Vahl, and Erigeron uniflorus L. ssp. eriocephalus (Vahl ex Hornen.) Cronq. sampled. The soil collected under these plants showed a high inoculum potential when tested at greenhouse conditions using Plantago lanceolata L. as a bait plant. Occasional occurrence of AM fungi was recorded in Festuca hyperborea Holmen ex Frederiksen, Trisetum spicatum (L.) Richt., and Potentilla hookeriana - Potentilla pulchella at Devon Island. Despite the fact that potential AM plants are present, no AM was found at the two most northern sites, Ellesmere Island and Ellef Ringnes Island. There seems to be climatic or dispersal limitations to AM colonization at these northern sites. Fine endophytic fungi, formerly named Glomus tenue (Grenall) I.R. Hall, were recorded at all four sites, but most frequently at Banks Island. We thereby provide further evidence that fine endophytes are more frequent in harsh climatic conditions than AM fungi. There was a relatively high proportion of nonmycorrhizal plant species at all sites, and this proportion increased towards the north

Lätt identifierbara försurningsindikatorer : En utvärderande sammanställning med förslag till möjliga försurningsindikatorer

Sammanfattning och slutsatser Information för 16 möjliga försurningsindikatorer, signalarter, har sammanställts i särskilda artpresentationer (se översikt i tabell på nästa sida). Dessa signalarter reagerar på försurningens drivkrafter svavel eller kväve, eller på dess effekter från marksurhet (pH) och/eller aluminiumhalt. Sju av de 16 signalarterna bedöms som särskilt lämpliga försurningsindikatorer för att deras reaktion är tydlig och för att de är välkända och lätta att studera. Fyra av dessa sju goda försurningsindikatorerna är växter av vilka två är utmärkta indikatorer för kväve, backsippa som minskar med ökat kväve och hallon som ökar med ökat kväve. Två andra växtarter svarar bra på förändringar i pH. En av dessa arter, harsyra, ökar när surheten ökar medan en annan, blåsippa, minskar när surheten ökar. En av de sju goda försurningsindikatorerna utgörs av en djurgrupp, brungrodor. Brungrodorna är vanlig groda, åkergroda och långbensgroda och de är känsliga för aluminium och minskar när aluminiumhalten ökar i det vatten där de växer upp. Deras ägg är också direkt påverkade av lågt pH i vattnet. Två av de sju goda försurningsindikatorerna är svampar. Den ena svamparten, kantarell, minskar när kvävemängden ökar och den andra, trattkantarell, ökar när det blir surare (pH sjunker). De övriga nio arterna fungerar mindre väl som försurningsindikatorer. Detta gäller för de fyra undersökta växtarterna, mosippa, ekorrbär, lungört och skogsbingel. Det gäller också för de tre djurgrupperna, vattensalamandrar (större och mindre vattensalamander), landsnäckor (en grupp med drygt 100 arter som t.ex. trädgårdssnäcka och vinbergssnäcka) och daggmaskar (en grupp med ca 20 arter) samt för fågelarten knipa. Inte heller den enda här studerade lavarten, lunglav, visade sig fungera bra som försurningsindikator. Vi föreslår att man fortsätter att arbeta vidare med de fyra arterna blåsippa, hallon, kantarell och trattkantarell. Dessa är sannolikt de mest lätt igenkännbara och mest allmänt spridda av de sju goda försurningsindikatorerna. Alla fyra speglar förhållanden i framför allt skogsmark, den livsmiljötyp där försurningstrycket sannolikt är störst idag. Två av dem svarar på ökat kvävenedfall: kantarell (minskar) och hallon (ökar). Kväve är sedan några år på väg att ta över svavlets roll som främsta drivkraft för det fortsatt höga försurningstrycket, och effekter av kvävenedfall är därför viktigt att följa. Två av de fyra är försurningsindikatorer som svarar på ökad syramängd, nämligen blåsippa (minskar) och trattkantarell (ökar). I skogsmarken är försurningsnivån idag fortfarande mycket hög och effekten av ändrad syramängd i skogsmark är därför viktig att kunna fortsätta följa. För de här föreslagna, fyra arterna behöver en uppföljnings- och redovisningsmetodik tas fram. Dessa metoder avses användas för att kunna föra en fruktbar dialog mellan allmänhet, myndigheter och forskare. Dialogen ska syfta till att driva åtgärdsarbetet snabbare fram mot ett minskat försurningshot och en snabbare återhämtning av påverkade livsmiljöer och arter

Foraging strategies of the external mycelium of the arbuscular mycorrhizal fungi Glomus intraradices and Scutellospora calospora

The responsiveness of the external mycelium of Glomus intraradices and Scutellospora calospora was tested in a multiple-choice experimental system in which mycelium encountered patches amended with nitrogen (N) or phosphorus (P), either alone or in combination with a host plant. We hypothesised that only AMF mycelium with sufficient supply of photo-synthate from an actively growing host would respond to the amendments provided. Mycelium was allowed to grow either 11 or 21 weeks before we analysed hyphal proliferation in amended patches introduced in mesh bags that were not reached by roots but by foraging mycelium only. Hyphal length, the AMF signature fatty acid 16:1w5, and root colonisation in new host plant seedlings were used to measure AMF growth and resource allocation in the patches. Mycelium from both fungal strains was able to colonise new host roots and sand in all patches but S. calospora was overall more responsive to the amendments than G. intraradices. G. intraradices grew equally into all patches, including the unamended control, whereas S. calospora produced significantly more hyphal length in the patch containing a host plant than in the rest of the patches. Both strains showed lower hyphal growth at the second harvest and mycelium of G. intraradices lost almost entirely its capacity to develop new mycelium in all choices presented. Lipid measurements showed this fungus did not use storage lipids to exploit the patches. S. calospora mycelium had reduced growth and colonisation ability but still showed some growth in the patches at the second harvest. A reduction in the content of NLFA 16:1w5 from the first to the second harvest suggested that S. calospora mycelium likely used storage lipids to sustain proliferation in the patches. The results indicated that S. calospora was more active and used more resources for foraging than G. intraradices; and that external mycelium foraging was maintained mainly with recently acquired plant carbon (C). This supported in general our hypothesis but showed as well that the two AMF strains had different strategies and resource allocation to forage. The overall low response of both AMF to the choices presented suggested that the responsiveness of mycelium searching freely in the substrate is lower than that observed in experimental systems in which the amendments have been placed in close contact with actively growing mycelium fronts in close vicinity with host roots

Phosphorus and carbon availability regulate structural composition and complexity of AM fungal mycelium.

The regulation of the structural composition and complexity of the mycelium of arbuscular mycorrhizal (AM) fungi is not well understood due to their obligate biotrophic nature. The aim of this study was to investigate the structure of extraradical mycelium at high and low availability of carbon (C) to the roots and phosphorus (P) to the fungus. We used monoxenic cultures of the AM fungus Rhizophagus irregularis (formerly Glomus intraradices) with transformed carrot roots as the host in a cultivation system including a root-free compartment into which the extraradical mycelium could grow. We found that high C availability increased hyphal length and spore production and anastomosis formation within individual mycelia. High P availability increased the formation of branched absorbing structures and reduced spore production and the overall length of runner hyphae. The complexity of the mycelium, as indicated by its fractal dimensions, increased with both high C and P availability. The results indicate that low P availability induces a growth pattern that reflects foraging for both P and C. Low C availability to AM roots could still support the explorative development of the mycelium when P availability was low. These findings help us to better understand the development of AM fungi in ecosystems with high P input and/or when plants are subjected to shading, grazing or any management practice that reduces the photosynthetic ability of the plant

A critical review of the use of lipid signature molecules for the quantification of arbuscular mycorrhiza fungi

Tools for accurate measurements of microbial biomass/abundance are imperative in soil ecology. This perspective was prompted by a lack of consistency in how the neutral lipid fatty acid (NLFA) and phospholipid fatty acid (PLFA) 16:1ω5 are used to estimate arbuscular mycorrhizal (AM) fungal abundance, which we argue can lead to erroneous conclusions within studies and complicate among-study comparisons. We show that more than half of all studies published to date use PLFA 16:1ω5 to quantify AM fungal biomass without proper controls. This is problematic because AM fungi cannot be separated from the bacterial contribution to this fatty acid signature. We provide a set of recommendations for future research and specifically urge researchers to extract and analyze NLFA 16:1ω5 for more accurate and sensitive assessments of AM fungal biomass as this can be done without doubling effort