Fine Endophyte Research Articles

The response of two Glomus mycorrhizal fungi and a fine endophyte to elevated atmospheric CO2, soil warming and drought

Abstract Plantago lanceolata plants were grown under various environmental conditions in association with the mycorrhizal fungi Glomus mosseae, G. caledonium and a fine endophyte either individually or all together. Using a time‐course approach, we investigated the effects of elevated atmospheric CO2 (eCO2), soil warming and drought and their interactions on root length colonized (RLC) by mycorrhizal fungi and extraradical mycorrhizal hyphal (EMH) production. Plant growth responded as would be expected to the environmental manipulations. There was no plant growth‐independent effect of eCO2 on mycorrhizal colonization; however, EMH production was stimulated by eCO2, i.e. there was increased partitioning of below‐ground carbon to the EMH. Soil warming directly stimulated both percent RLC by the Glomus species and EMH density; soil warming did not affect RLC by the fine endophyte. Drought decreased percent RLC for the fine endophyte, but not for the Glomus species. The presence of one mycorrhizal fungus did not affect the response of another to the environmental variables. There was no evidence of any interactive effects of the environmental variables on RLC, but there were significant environmental interactions on EMH production. In particular, the stimulatory effects of eCO2 and soil warming on EMH density were not additive. The results are discussed in terms of the soil carbon cycle, highlighting some crucial gaps in our knowledge. If future environmental changes affect mycorrhizal fungal turnover and respiration, then this could have important implications for the terrestrial carbon cycle.

Mycorrhizal inoculum potentials of pure reclamation materials and revegetated tailing sands from the Canadian oil sand industry

Recent improvements in the management of oil sand tailings used by the Canadian oil sand industry have resulted in the production of composite tailing sands (CT): a new challenging material for reclamation work. Jack pine (Pinus banksiana Lamb.), hybrid poplar (Populus deltoides Bartr. ex Marsh. xPopulus nigra L.) and red clover (Trifolium pratense L.) plants were used in an 8-week greenhouse bioassay to evaluate the mycorrhizal inoculum potential of CT. This inoculum potential was compared with that of three other reclamation materials [common tailing sands (TS), deep overburden (OB) and muskeg peat (MK)], and with three sites reclaimed in 1982 (R82), 1988 (R88) and 1999 (R99). CT was devoid of active mycorrhizal propagules while all other materials showed some level of inoculum potential. Arbuscular mycorrhizal fungi were observed on roots of clover or poplar grown in TS, OB, and all substrates containing peat (MK, R82, R88 and R99). Pine roots were also colonized by vesicle-forming hyphae of an unidentified fine endophyte and by dark septate fungi. Ectomycorrhizas (ECM) were observed on pine and poplar grown in OB, MK, and in soils from the two older reclaimed sites (R82 and R88). Using morpho- and molecular typing, six ECM fungi were identified to the genus or species level: Laccaria sp., Thelephora americana, Wilcoxina sp. (E-strain), Tuber sp. (I-type), a Sebacinoid, and a Pezizales species. Laccaria sp. and Wilcoxina sp. were the most frequently observed ECM species.

Root Fungus Colonization along an Altitudinal Gradient in North Norway

Mycorrhizal symbiosis is generally advantageous for plants in nutrient-poor soils, but this advantage may be low in arcto-alpine conditions. While the relative coverage of nonmycorrhizal plant species has been found to increase along an altitudinal gradient, the within-species patterns of mycorrhizal colonization in arctic and alpine plants are not well known, and different results have been obtained in relation to altitude. We investigated arbuscular mycorrhizal (AM) and dark-septate endophytic (DSE) root colonization in six subarctic herbaceous plants Ranunculus glacialis L., Saxifraga aizoides L., Sibbaldia procumbens L., Solidago virgaurea L., Trientalis europaea L., and Viola biflora L. along an altitudinal gradient (0–1400 m a.s.l.) at Mt. Paras, North Norway. We did not find any consistent decline in the different types of fungus colonization along the entire gradient. There was no statistically significant shift in coarse AM or DSE colonization with altitude. However, fine endophyte type AM colonization showed a statistically significant, positive relationship with altitude. These results suggest that root colonization of any particular mycorrhizal species may yield different gradient patterns with altitude than the relative coverages of mycorrhizal and nonmycorrhizal plant taxa. Because of its positive association with altitude, fine endophyte colonization may have a specific role in the nutrition of arctic and alpine plants.

Seasonal and edaphic variation in VAM infection of fuel wood trees by Glomus mosseae

Seasonal differences in percentage length of fuel-wood host roots, viz., Albizia lebbeck, Acacia nilotica and Prosopis juliflora infected with Glomus mosseae were measured in five field sites in Mainpuri District of U.P. Highest G. mosseae infection levels were generally found in the rainy season in phosphorus deficient soils, low in moisture. The root sampled from the soils with a high soil-moisture content, fine endophyte infection increased to a maximum later in the growing season. A higher percentage frequency of fine endophyte infection on fine fuel-wood feeder roots in rainy season is taken as evidence for the hypothesis that G. mosseae is a vesicular arbuscular mycorrhizal fungus particularly adapted to penetrating host roots during brief seasonal fluxes of phosphorus availability. The implications of these data are discussed in relation to mechanisms in fuel-wood trees which adapt them to nutrient stress.

Arbuscular mycorrhizae respond to plants exposed to elevated atmospheric CO2 as a function of soil depth

The importance of arbuscular mycorrhizae (AM) in plant and ecosystem responses to global changes, e.g. elevated atmospheric CO2, is widely acknowledged. Frequently, increases in AM root colonization occur in response to increased CO2, but also the lack of significant changes has been reported. The goal of this study was to test whether arbuscular mycorrhizae (root colonization and composition of root colonization) respond to plants grown in elevated CO2 as a function of soil depth. We grew Bromus hordeaceus L. and Lotus wrangelianus Fischer & C. Meyer monocultures in large pots with a synthetic serpentine soil profile for 4 yr in an experiment, in which CO2 concentration was crossed factorially with NPK fertilization. When analyzing root infection separately for topsoil (0–15 cm) and subsoil (15–45 cm), we found large (e.g., about 5-fold) increases of AM fungal root colonization in the subsoil in response to CO2, but no significant changes in the corresponding topsoil of Bromus. Only the coarse endophyte AM fungi, not the fine endophyte AM fungi, were responsible for the observed increase in the bottom soil layer, indicating a depth-dependent shift in the AM community colonizing the roots, even at this coarse morphological level. Other response variables also had significant soil layer * CO2 interaction terms. The subsoil response would have been hidden in an unstratified assessment of the total root system, since most of the root length was concentrated in the top soil layer. The increased presence of mycorrhizae in roots deeper in the soil should be considered in sampling protocols, as it may be indicative of changed patterns of nutrient acquisition and carbon sequestration.

Morphology and infectivity of fine endophyte in a mediterranean environment

This study investigated the morphology and infectivity of fine endophyte in a mediterranean environment. Five morphological groups of fine endophyte differing in up to 11 characters were present within two pot cultures of fine endophyte from southwestern Australia. Occurrence and abundance of a particular type of fine endophyte were not affected by the application of calcium carbonate. It appeared that there may be more than one fungus included among the two sources of fine endophyte, however it was not possible to separate the fungi. A second experiment demonstrated that infective propagules of fine endophyte can be very small (< 38 μm) and fresh roots acted as a potential source of infective propagules. There was no infectivity of fine endophyte in the soil at the end of the growing season but it reoccurred in similar quantity in the next growing season.

Fungal root colonization responses in natural grasslands after long‐term exposure to elevated atmospheric CO2

SummaryArbuscular mycorrhizae, ubiquitous mutualistic symbioses between plant roots and fungi in the order Glomales, are believed to be important controllers of plant responses to global change, in particular to elevated atmospheric CO2. In order to test if any effects on the symbiosis can persist after long‐term treatment, we examined root colonization by arbuscular mycorrhizal (AM) and other fungi of several plant species from two grassland communities after continuous exposure to elevated atmospheric CO2 for six growing seasons in the field. For plant species from both a sandstone and a serpentine annual grassland there was evidence for changes in fungal root colonization, with changes occurring as a function of plant host species. We documented decreases in percentage nonmycorrhizal fungal root colonization in elevated CO2 for several plant species. Total AM root colonization (%) only increased significantly for one out of the five plant species in each grassland. However, when dividing AM fungal hyphae into two groups of hyphae (fine endophyte and coarse endophyte), we could document significant responses of AM fungi that were hidden when only total percentage colonization was measured. We also documented changes in elevated CO2 in the percentage of root colonized by both AM hyphal types simultaneously. Our results demonstrate that changes in fungal root colonization can occur after long‐term CO2 enrichment, and that the level of resolution of the study of AM fungal responses may have to be increased to uncover significant changes to the CO2 treatment. This study is also one of the first to document compositional changes in the AM fungi colonizing roots of plants grown in elevated CO2. Although it is difficult to relate the structural data directly to functional changes, possible implications of the observed changes for plant communities are discussed.

Patterns of arbuscular mycorrhiza colonisation of the roots of Hyacinthoides non-scripta after disruption of soil mycelium

Early-season colonisation of new roots of Hyacinthoides non-scripta (L.) Chouard ex Rothm. was investigated to determine how arbuscular mycorrhizal symbiosis is re-established after the annual root system is shed. During the rootless phase in summer, colonies of bulbs were removed and replanted after the soil around and below the bulb had been mixed (major disturbance) so as to disrupt the external mycelium of arbuscular mycorrhizal (AM) fungi. As a minor disturbance treatment, top soil was removed, bulbs were turned or not in their growth position with as little other disturbance as possible, and the top soil replaced. Control plants were left undisturbed. Half of the plants were harvested 3–4 weeks after the onset of root emergence. Populations of all AM fungi in roots were greatly reduced by major disturbance, whilst those in other treatments and controls were unaffected. At the second harvest, in spring, when shoots had emerged, root colonisation by fine endophytes and Scutellospora morphotypes developed in all treatments, whereas that of Acaulospora morphotypes remained low after major disturbance. Disturbance treatments delayed the appearance, at the second harvest, of mycorrhizas with degenerate arbuscules. Leaf phosphorus concentration was unaffected by soil disturbance, possibly due to partial recovery of AM fungal populations or buffering by resources stored in the bulb.

The effect of rain in the dry-season on the formation of vesicular-arbuscular mycorrhizas in the growing season of annual clover-based pastures.

In a mediterranean climate with hot dry summers and cool winter growing seasons, rain in summer may initiate seed germination and seedling emergence in annual clover-based pastures. If soil moisture becomes limiting and the seedlings die before the onset of winter rains then a'false break'has occurred. The effect of false breaks on the formation of mycorrhizas in subterranean clover (Trifolium subterraneum L.) in the winter growing season was investigated. Undisturbed cores were collected in the summer from two annual clover-based pastures in Western Australia. The cores were treated with one or two false breaks, or left dry. For each false break, 3 centimetres of water were applied to the surface of the core over a 3 day period and then the cores were let dry in glasshouse conditions. The second false break and the growing season were initiated after the complete death of plants that had emerged in the previous cycle. The growing season was simulated by watering all cores to field capacity and planting to a uniform stand of subterranean clover. Mycorrhizal colonization in the growing season was decreased by false breaks with little difference between One and two false breaks. In one soil, the percentage of the root length containing arbuscules (AC%) at 14 d after planting in the growing season was decreased from 52 to 33% by false breaks and at 42 d after planting from 16 to 46%. In the other soil, the AC% at 28 d after planting in the growing season was decreased from 72 to 55% by false breaks. Assessment of the morphology of the mycorrhizas indicated that colonization by fine endophytes was decreased but colonization by Acaulospora spp., Glomus spp. and Scutellospora and Gigaspora spp. was not decreased by false breaks. Shoot phosphorus concentration at 14 d after planting and shoot dry mass at 42 d after planting were decreased by false breaks in only one soil.

Vesicular-arbuscular mycorrhizal fungi, particularly Glomus tenue, in Venezuelan bromeliad epiphytes

The mycorrhizal status of water-impounding “tank” bromeliad epiphytes from three locales differing in altitude and moisture regime within Venezuelan cloud forest was examined. Species of vesicular-arbuscular mycorrhizal (VAM) fungi found in arboreal soils were compared to VAM fungi found in terrestrial soils. Sixteen of the 19 epiphytes examined for the presence of VAM fungi had roots with infection stages; 14 of these specimens showed growth of the fine endophyte Glomus tenue. Fine endophyte was the only VAM fungus found associated with epiphytes in the driest locale studied, while coarse VAM fungi (Gigaspora and Scutellospora spp.) were found at sampling locales receiving more moisture. Root infection was usually composed of intercellular hyphae and peletons; few arbuscules were observed. However, abundant extracellular hyphae were often observed tangled about roots in arboreal soil. It is concluded that epiphytic bromeliads probably benefit, at least periodically, from VAM fungi scavenging for sporadically available nutrients in arboreal soils. Glomus tenue may be particularly important as a colonizing VAM fungus in drier sites of Venezuelan cloud forest. The species composition of VAM fungi in arboreal soils was different to that of terrestrial soils sampled directly under epiphytic bromeliad perches, suggesting that VAM fungi species associated with bromeliads are dispersed to their hosts by vagile animal vectors.

Vesicular-arbuscular mycorrhiza infection in cut grassland following long-term slurry application

Herbage root samples from a long-term field experiment in which pig and cow slurries had been applied to cut grassland for 19 yr were examined for vesicular-arbuscular (VA) mycorrhiza.There were fertilized and unfertilized controls and three application rates (50,100 and 200 m 3 ha −1 yr −1) of both types of slurry, with six replicate plots in randomized blocks.Soil samples were analysed for pH (in water), “total” Cu and Zn, EDTA-extractable Cu and Zn and NaHC0 3-extractable P.The proportions of Lolium perenne, Agrostis stolonifera and Poa spp in the herbage dry matter at the first cut of 1989 were also determined. Despite contrasting long-term effects of the two types of slurry on soil pH, increasing application rate of both pig and cow slurries produced a marked decrease in overall mycorrhizal infection of plant roots in the sward with a corresponding increase in infection by the fine endophyte, Glomus tenue.Calculated correlation coefficients showed that mycorrhizal infection was related to soil extraetable P,Cu, Zn and pH and also to differences in sward botanical composition,especially the proportion of L. perenne. Furthermore, stepwise multiple regression analysis identified soil chemical properties, especially total Zn and pH, as the more important explanatory variables in preference to botanical composition.

Alteration of growth ofSolanum opacum andPlantago drummondii and inhibition of regrowth of hyphae of vesicular-arbuscular mycorrhizal fungi from dried root pieces by manganese

Addition of MnSO4 or MnCl2 to a fine sandy soil from South Australia had a negative effect on shoot growth and root elongation ofSolanum opacum in the absence of significant presence of vesicular-arbuscular mycorrhiza (VAM). VAM ameliorated the reduction of plant growth by Mn, even though mycorrhizal development was decreased. Mn inhibited infection of roots by a fine endophyte less than that by some coarse endophytes. High concentrations of available Mn inhibited growth of hyphae of VAM fungi from dried root pieces, a significant source of infection by mycorrhizal fungi in the soil used.

Early development of vesicular-arbuscular mycorrhizas in autumn-sown cereals

Fractional infection of roots of winter cereals (wheat, barley and rye) by vesicular-arbuscular mycorrhizal fungi was monitored in three fields in south-east England over three successive seasons. In most cases there was a peak in fractional infection (up to 60% root length infected) in the period from November to December. This extensive development of mycorrhizas during this period has not previously been noted in winter cereals, and has importance as a determinant of the growth response of annual crops. Differences in experimental technique may have led to this phenomenon being overlooked in earlier work. Fractional infection levels then either dropped sharply or continued to rise gradually until late spring in the three seasons studied. In all cases, a second peak in arbuscular development was noted just prior to ear formation, followed by a post-anthesis decline. These fluctuations in fractional infection have been compared with similar trends recorded for dry weight increases of roots over a winter cereal season, and may be influenced by date of sowing. The winter decrease in fractional infection by VAM noted in two out of the three seasons was apparently due to a relative reduction in the coarse endophytic component of the mycorrhizal association. In contrast, infection due to fine endophytes was more stable and persisted as the major proportion of the association throughout the winter and post-anthesis declines in fractional infection.

MICROBIAL ACTIVITY AND MYCORRHIZAL POTENTIAL OF FOUR OVERBURDEN TYPES USED IN THE RECLAMATION OF EXTRACTED OIL SANDS

Slender wheatgrass and jack pine were grown in the greenhouse in cores containing a bottom layer of extracted oil sands with four overburdens individually layered over the sand. The overburdens included a muskeg peat, two shallow mineral overburdens and a deep overburden. Mycorrhizal development, microbial respiration and biomass and the degree of decomposition of slender wheatgrass roots in litter bags were determined in each plant species-overburden combination. Both ecto- and vesicular-arbuscular (VA) mycorrhizal inoculum was present in all four overburdens. The symbionts of slender wheatgrass were the "fine endophyte" and Glomus aggregatum. VA development was very low in peat whereas plants in the shallow overburdens became heavily mycorrhizal. Infection did not spread from the overburden layer to roots in the tailing sand. Jack pine roots in the peat and two shallow overburdens were heavily infected after 4 months. The most common symbiont was an ascomycete known as the E-strain. Microbial respiration was highest in the peat and was not influenced by plant species. Microbial biomass was also highest in the peat and much lower in the mineral overburdens. Only in the peat was the amount of microbial biomass larger with slender wheatgrass than with jack pine. Slender wheatgrass roots decomposed most rapidly in the peat overburden and least rapidly in the deep overburden. Key words: Microbial activity, jack pine, slender wheatgrass, mycorrhizae, reclamation, oil sands

Infectivity of vesicular arbuscular mycorrhizal fungi in agricultural soils

The development of vesicular arbuscular (VA) mycorrhizas was followed for subterranean clover grown in 20 field soils in a glasshouse experiment. The aims of the study were: to understand the way in which mycorrhizas develop in field soils; to identify those factors which could be used to predict field sites suitable for inoculation with VA mycorrhizal fungi. In each soil, the amount and rate of mycorrhiza formation were estimated for species of each genus represented. The data were examined in relation to differences among soils in numbers of spores of VA mycorrhizal fungi and in soil properties. A poor correlation between total spore numbers and the total amount and rate of infection formed was attributed to two factors. First, infection by fine endophyte (a fungus which does not form large spores that can be counted) was ubiquitous, but the amount of mycorrhizas formed by this fungus varied greatly. Second, species of fungi differed in their rates of infection. In general, there was an association between spore numbers and infection development for individual fungal species. The development of mycorrhizas in any soil fell into one of three categories: I, rapid and extensive; II, extensive but with a lag phase; III, slow and limited in extent. The species of fungi in soils from each category were similar. Category I included the soils which were most deficient in phosphorus for plant growth. However, from measurements of soil properties alone, it is not possible to predict those soils which are suitable for the introduction of inoculant VA mycorrhizal fungi.

OBSERVATIONS ON THE MYCORRHIZAL STATUS OF SOME ALPINE PLANT COMMUNITIES

SUMMARYIn some Austrian alpine plant communities, levels of vesicular‐arbuscular mycorrhizal infection are highest in closed herb‐rich communities of intermediate altitudes (1900 to 2500 m). In fertilized hay meadows of lower altitudes (1600 m) and in the nival zone above 3000 m, endogonaceous infection is light. In the latter, it is mainly by the fine endophyte, Glomus tenuis. Many plants throughout the altitudinal range of the survey are infected with dark septate hyphae and, in the Cyperaceae, this is the dominant infection. Ectomycorrhizas occur on some herbaceous species as well as on Salix up to 2500 m. The possible significance of the infection patterns is discussed.

Fungal associations of roots of dominant and sub-dominant plants in high-alpine vegetation systems with special reference to mycorrhiza.

Types of root infection were analysed in healthy dominant and sub-dominant plants of zonal and azonal vegetation above the timberline in the Central and Northern Calcareous Alps of Austria. In the open nival zone vegetation, infection by fungi of the Rhizoctonia type was predominant, vesicular-arbuscular mycorrhizal infection, which was mostly of the fine endophyte (Glomus tenuis) type, being light and mainly restricted to grasses in closed vegetation patches. More extensive Glomus tenuis infection was found in the alpine grass heath, but in Carex, Rhizoctonia was again the most important fungus. The ericaceous plants of the dwarf shrub heath have typical ericoid infection, but quantitative analysis reveals a decrease of infection intensity with increase of altitude. The possible function of the various types of root infection are discussed, and the status of Rhizoctonia as a possible mycorrhizal fungus is considered.

SEASONAL AND EDAPHIC VARIATION IN VESICULAR‐ARBUSCULAR MYCORRHIZAL INFECTION OF GRASSES BY GLOMUS TENUIS

SummarySeasonal differences in percentage length of gramineous host root infected with Glomus tennis were measured in three field sites in Pennsylvania, U.S.A. Highest G. tennis infection levels were generally found in the spring in very phosphorus‐deficient soils low in moisture. In roots sampled from soils with a high spring soil‐moisture content, fine endophyte infection increased to a maximum later in the growing season. A higher percentage frequency of fine endophyte infection on fine grass feeder roots in spring is taken as evidence for the hypothesis that G. tenuis is a vesicular–arbuscular mycorrhizal fungus particularly adapted to penetrating host roots during brief seasonal fluxes of phosphorus availability. The implications of these data are discussed in relation to mechanisms in grasses which adapt them to nutrient stress.

The 'most probable number' method for enumerating infective propagules of vesicular arbuscular mycorrhizal fungi in soil

Estimates of the number of infective propagules of vesicular-arbuscular (VA) endophytes in two soils were obtained using a most probable number (MPN) method. These estimates were compared with counts of the number of spores in the same soils obtained using a conventional wet sieving method. In one soil, there was good agreement between the number of coarse endophyte propagules, estimated by the MPN technique, and the number of germinable spores extracted using the wet sieving technique. However, a large population of fine endophyte propagules (more than 230 per 50 g soil) could only be enumerated using the MPN technique. In the second soil, fewer coarse endophyte propagules were found using the wet sieving technique than when using the MPN technique. The MPN technique appears to give a more realistic estimate of the number of infective propagules of VA endophytes in field soils than the conventional method.

The Distribution and Abundance of Vesicular Arbuscular Endophytes in Some Western Australian Soils

The distribution and abundance of large-spored vesicular arbuscular (VA) endophytes was examined at three localities in Western Australia. Within each locality, soil samples were collected from sites with a range of soil properties and superphosphate histories. Vesicular arbuscular endophytes were widespread. Spores were found in all but five of 104 samples. In two of the samples where spores were not found, plants grown in the soils formed VA mycorrhizas. Root infection by a fine endophyte resembling Rhizophagus tenuis was also frequently observed. Five spore types were found. Honey-coloured sessile spores were present in 85% of the samples. The yellow vacuolate spore type was the second most common endophyte, but its distribution was mostly limited to cultivated and fertilized soils. Endophytes other than the yellow vacuolate spore type occurred on both virgin and agricultural soils. The distribution of honey-coloured sessile and yellow vacuolate spores in cultivated soils appeared to be associated with variation in soil pH. The total numbers of spores collected on a 106 μm sieve were not correlated with soil pH, NaHCO3-extractable phosphorus or superphosphate history.