Response of 11 eucalyptus species to inoculation with three arbuscular mycorrhizal fungi

 Numerous publications have reported growth stimulation of Eucalyptus following ectomycorrhizal inoculation in nursery or field conditions. Although Eucalyptus species can also form arbuscular mycorrhiza, their dependency on this type of mycorrhiza is still debatable. This paper presents information on the effect of inoculation of arbuscular mycorrhizal fungi on eucalypt growth. Twenty weeks after mycorrhizal inoculation, Eucalyptus seedlings' stem dry weight could be increased up to 49% compared to non-inoculated control plants. Intensity of root colonization by a given fungus depended on the host species, but it was not related to a plant growth response. Leaf phosphorus concentration of non-inoculated Eucalyptus seedlings varied greatly between species. Increases in leaf phosphorus concentration following mycorrhizal infection were not necessarily associated with plant growth stimulation. The most mycorrhiza-dependent Eucalyptus species tended to be those having the highest leaf phosphorus concentration in the absence of a fungal symbiont. These mycorrhiza-dependent Eucalyptus species seem to have greater phosphorus requirements and consequently to rely more on the symbiotic association. Accepted: 1 September 1995     

Responses of soil microbial catabolic diversity to arbuscular mycorrhizal inoculation and soil disinfection

Although it is usually admitted that arbuscular mycorrhizal (AM) fungi are key components in soil bio-functioning, little is known on the response of microbial functional diversity to AM inoculation. The aims of the present study were to determine the influence of Glomus intraradices inoculum densities on plant growth and soil microflora functional diversity in autoclaved soil or non-disinfected soil. Microbial diversity of soil treatments was assessed by measuring the patterns of in situ catabolic potential of microbial communities. The soil disinfection increased sorghum growth, but lowered catabolic evenness (4.8) compared to that recorded in the non-disinfected soil (6.5). G. intraradices inoculation induced a higher plant growth in the autoclaved soil than in the non-disinfected soil. This AM effect was positively related to inoculum density. Catabolic evenness and richness were positively correlated with the number of inoculated AM propagules in the autoclaved soil, but negatively correlated in the non-disinfected soil. In addition, after soil disinfection and AM inoculation, these microbial functionality indicators had higher values than in the autoclaved or in the non-disinfected soil without AM inoculation. These results are discussed in relation to the ecological influence of AM inoculation, with selected fungal strains and their associated microflora on native soil microbial activity.     

Different growth response of five co-existing stoloniferous plant species to inoculation with native arbuscular mycorrhizal fungi

Five species of stoloniferous plants originating from the same field site (Galeobdolon montanum, Glechoma hederacea, Potentilla anserina, Ranunculus repens and Trifolium repens) were studied with respect to their interaction with arbuscular mycorrhizal (AM) fungi. More specifically, the question was addressed whether mycorrhizal growth response of host plant species could be related to their vegetative mobility. The roots of all the species examined were colonised with AM fungi in the field, with the percentage of colonisation varying among species from approximately 40% to 90%. In a subsequent pot experiment, plants of all the species were either left non-inoculated or were inoculated with a mixture of three native AM fungi isolated from the site of plant origin (Glomus mosseae, G. intraradices and G. microaggregatum). AM fungi increased phosphorus uptake in all the plant species; however, plant growth response to inoculation varied widely from negative to positive. In addition to the biomass response, AM inoculation led to a change in clonal growth traits such as stolon number and length or ramet number in some species. Possible causes of the observed differences in mycorrhizal growth response of various stoloniferous plants are discussed.     

Effects of arbuscular mycorrhizal fungi and soil developmental stages on herbaceous plants growing in the early stage of primary succession on Mount Fuji

A pot culture experiment was conducted to examine the effects of arbuscular mycorrhizal (AM) fungi and soil developmental stages on the growth and nutrient absorption of pioneer plants growing in the early stage of primary succession on Mt. Fuji. Four herbaceous plants, Polygonum cuspidatum (Polygonaceae), Miscanthus oligostachyus (Gramineae), Aster ageratoides var. ovatus (Compositae), and Hedysarum vicioides (Leguminosae), were grown from seed in soils collected from two different successional stages, bare ground and an herbaceous plant community. Spores of indigenous AM fungi collected from the herbaceous plant community were used as inoculum. The initial colonizer P. cuspidatum showed very low levels of AM colonization (<0.4%), whereas the average AM colonization levels of M. oligostachyus, A. ageratoides var. ovatus, and H. vicioides were within the range of 13–49%. AM fungi had positive effects on the growth and N acquisition of the leguminous species (H. vicioides) irrespective of soil developmental stages. In contrast, AM colonization did not increase the plant dry weight and N content of the non-leguminous species (P. cuspidatum, M. oligostachyus, and A. ageratoides var. ovatus) in both soil developmental stages. A positive effect of AM colonization on P content was observed in M. oligostachyus, A. ageratoides var. ovatus, and H. vicioides only in soil collected from the herbaceous plant community. P. cuspidatum showed no or a negative response to AM colonization in all cases. These results suggest that the effect of AM fungi on plant growth depends more on the plant species than soil developmental stages in the early stage of primary succession in this volcanic area.     

Response of strawberry to inoculation with arbuscular mycorrhizal fungi under very high soil phosphorus conditions

A field study was done to assess the potential benefit of arbuscular mycorrhizal (AM) inoculation of elite strawberry plants on plant multiplication, under typical strawberry nursery conditions and, in particular, high soil P fertility (Mehlich-3 extractible P=498 mg kg⁻¹). Commercially in vitro propagated elite plants of five cultivars (‘Chambly,’ ‘Glooscap,’ ‘Joliette,’ ‘Kent,’ and ‘Sweet Charlie’) were transplanted in noninoculated growth substrate or in substrate inoculated with Glomus intraradices or with a mixture of species (G. intraradices, Glomus mosseae, and Glomus etunicatum) at the acclimation stage and were grown for 6 weeks before transplantation in the field. We found that AM fungi can impact on plant productivity in a soil classified as excessively rich in P. Inoculated mother plants produced about 25% fewer daughter plants than the control in Chambly (P=0.03), and Glooscap produced about 50% more (P=0.008) daughter plants when inoculated with G. intraradices, while the productivity of other cultivars was not significantly decreased. Daughter plant shoot mass was not affected by treatments, but their roots had lower, higher, or similar mass, depending on the cultivar–inoculum combination. Root mass was unrelated to plant number. The average level of AM colonization of daughter plants produced by noninoculated mother plants did not exceed 2%, whereas plants produced from inoculated mothers had over 10% of their root length colonized 7 weeks after transplantation of mother plants and ∼6% after 14 weeks (harvest), suggesting that the AM fungi brought into the field by inoculated mother plants had established and spread up to the daughter plants. The host or nonhost nature of the crop species preceding strawberry plant production (barley or buckwheat) had no effect on soil mycorrhizal potential, on mother plant productivity, or on daughter plant mycorrhizal development. Thus, in soil excessively rich in P, inoculation may be the only option for management of the symbiosis.     

Building a mycorrhizal cell: How to reach compatibility between plants and arbuscular mycorrhizal fungi

Abstract

Arbuscular mycorrhizal fungi occur throughout the majority of ecosystems supporting host plant nutrition. Recent findings describe the accommodation of the fungus by the root cell as a crucial step for compatibility between the partners. We discuss here the novel aspects of cellular plant-fungus interactions, with a particular attention to the interface compartment, the unique apoplastic space hosting intracellular fungal structures. The main features of arbuscular mycorrhizal colonization are examined and recent information in the field of plant and fungal cell responses during the establishment of the symbiosis is discussed. Differences between the colonization of root epidermal and cortical tissues are discussed, highlighting the growing interest in the role of epidermal cells during the first and decisive steps of the symbiosis. New approaches such as root organ cultures, in vivo observations, GFP tagging and mutant plant analysis are commented on and information from these is compared with that gained from more traditional methods. In particular, the use of plant mutants is depicted as a powerful tool for dissecting and understanding the genetic and cellular aspects of plant/fungus compatibility. Finally, perspectives in this field are outlined through the application of these approaches to the currently unanswered questions.     

Studies of iron transport by arbuscular mycorrhizal hyphae from soil to peanut and sorghum plants

 The influence of an arbuscular mycorrhizal (AM) fungus on phosphorus (P) and iron (Fe) uptake of peanut (Arachis hypogea L.) and sorghum (Sorghum bicolor L.) plants was studied in a pot experiment under controlled environmental conditions. The plants were grown for 10 weeks in pots containing sterilised calcareous soil with two levels of Fe supply. The soil was inoculated with rhizosphere microorganisms only or with rhizosphere microorganisms together with an AM fungus (Glomus mosseae [Nicol. & Gerd.] Gerdemann & Trappe). An additional small soil compartment accessible to hyphae but not roots was added to each pot after 6 weeks of plant growth. Radiolabelled P and Fe were supplied to the hyphae compartment 2 weeks after addition of this compartment. After a further 2 weeks, plants were harvested and shoots were analysed for radiolabelled elements. In both plant species, P uptake from the labelled soil increased significantly more in shoots of mycorrhizal plants than non-mycorrhizal plants, thus confirming the well-known activity of the fungus in P uptake. Mycorrhizal inoculation had no significant influence on the concentration of labelled Fe in shoots of peanut plants. In contrast, ⁵⁹Fe increased in shoots of mycorrhizal sorghum plants. The uptake of Fe from labelled soil by sorghum was particularly high under conditions producing a low Fe nutritional status of the plants. These results are preliminary evidence that hyphae of an arbuscular mycorrhizal fungus can mobilise and/or take up Fe from soil and translocate it to the plant. Accepted: 6 March 1998     

Dispersal of arbuscular mycorrhizal fungi and plants during succession

Arbuscular mycorrhizal (AM) fungi are important root symbionts that enhance plant nutrient uptake and tolerance to pathogens and drought. While the role of plant dispersal in shaping successional vegetation is well studied, there is very little information about the dispersal abilities of AM fungi. We conducted a trap-box experiment in a recently abandoned quarry at 10 different distances from the quarry edge (i.e. the potential propagule source) over eleven months to assess the short term, within-year, arrival of plant and AM fungal assemblages and hence their dispersal abilities. Using DNA based techniques we identified AM fungal taxa and analyzed their phylogenetic diversity. Plant diversity was determined by transporting trap soil to a greenhouse and identifying emerging seedlings. We recorded 30 AM fungal taxa. These contained a high proportion of ruderal AM fungi (30% of taxa, 79% of sequences) but the richness and abundance of AM fungi were not related to the distance from the presumed propagule source. The number of sequences of AM fungi decreased over time. Twenty seven plant species (30% of them ruderal) were recorded from the soil seed traps. Plant diversity decreased with distance from the propagule source and increased over time. Our data show that AM fungi with ruderal traits can be fast colonizers of early successional habitats.     

Improvement of Cupressus atlantica Gaussen growth by inoculation with native arbuscular mycorrhizal fungi

AIMS: The study aimed to determine whether inoculation with native arbuscular mycorrhizal (AM) fungi could improve survival and growth of seedlings in degraded soils of Morocco. METHODS AND RESULTS: Soil samples were collected from the rhizosphere of Cupressus atlantica trees in the N'Fis valley (Haut Atlas, Morocco). AM spores were extracted from the soil, identified and this mixture of native AM fungi was propagated on maize for 12 weeks on a sterilized soil to enrich the fungal inoculum. Then C. atlantica seedlings were inoculated with and without (control) mycorrhizal maize roots, cultured in glasshouse conditions and further, transplanted into the field. The experiment was a randomized block design with one factor and three replication blocks. The results showed that a high AM fungal diversity was associated with C. atlantica; native AM fungi inoculation was very effective on the growth of C. atlantica seedlings in glasshouse conditions and this plant growth stimulation was maintained for 1 year after outplanting. CONCLUSIONS: Inoculation of C. atlantica with AM fungi increased growth and survival in greenhouse and field. SIGNIFICANCE AND IMPACT OF THE STUDY: The data indicate that use of native species of AM fungi may accelerate reforestation of degraded soils. Further studies have to be performed to determine the persistence of these mycorrhizae for a longer period of plantation and to measure the effects of this microbial inoculation on soil biofunctioning.     

Early responses of wild plant seedlings to arbuscular mycorrhizal fungi and pathogens

Many plants form associations with arbuscular mycorrhizal fungi (AMF) because they profit from improved phosphorus nutrition and from protection against pathogens. Whereas mycorrhiza-induced pathogen protection is well understood in agricultural plant species, it is rarely studied in wild plants. As many pathogens infest plants in the first days after germination, mycorrhiza-induced pathogen protection may be especially important in the first few weeks of plant establishment.Here, we investigated interacting effects of AMF and the seedling pathogen Pythium ultimum on the performance of six- to seven-week-old seedlings of six wild plant species of the family Asteraceae in a full factorial experiment.Plant species differed in their response to AMF, the pathogen and their interactions. AMF increased and the pathogen decreased plant biomass in one and three species, respectively. Two plant species were negatively affected by AMF in the absence, but positively or not affected in the presence of the pathogen, indicating protection by AMF. This mycorrhiza-induced pathogen protection is especially surprising as we could not detect mycorrhizal structure in the roots of any of the plants.Our results show that even seedlings without established intraradical hyphal network can profit from AMF, both in terms of growth promotion in the absence of a pathogen and pathogen protection. The function of AMF is highly species-specific, but tends to be similar for more closely related plant species, suggesting a phylogenetic component of mycorrhizal function. Further studies should test a wider range of plant species, as our study was restricted to one plant family, and investigate whether plants profit from early mycorrhizal benefits in the long term.     

Different native arbuscular mycorrhizal fungi influence the coexistence of two plant species in a highly alkaline anthropogenic sediment

Different species of arbuscular mycorrhizal fungi (AMF) can produce different amounts of extraradical mycelium (ERM) with differing architectures. They also have different efficiencies in gathering phosphate from the soil. These differences in phosphate uptake and ERM length or architecture may contribute to differential growth responses of plants and this may be an important contributor to plant species coexistence. The effects of the development of the ERM of AMF on the coexistence of two co-occurring plant species were investigated in root-free hyphal chambers in a rhizobox experimental unit. The dominant shrub (Salix atrocinerea Brot.) and herbaceous (Conyza bilbaoana J. Rémy) plant species found in a highly alkaline anthropogenic sediment were studied in symbiosis with four native AMF species (Glomus intraradices BEG163, Glomus mosseae BEG198, Glomus geosporum BEG199 and Glomus claroideum BEG210) that were the most abundant members of the AMF community found in the sediment. Different AMF species did not influence total plant productivity (sum of the biomass of C. bilbaoana and S. atrocinerea), but had a great impact on the individual biomass of each plant species. The AMF species with greater extracted ERM lengths (G. mosseae BEG198, G. claroideum BEG210 and the four mixed AMF) preferentially benefited the plant species with a high mycorrhizal dependency (C. bilbaoana), while the AMF species with the smallest ERM length (G. geosporum BEG199) benefited the plant species with a low mycorrhizal dependency (S. atrocinerea). Seed production of C. bilbaoana was only observed in plants inoculated with G. mosseae BEG198, G. claroideum BEG210 or the mixture of the four AMF. Our results show that AMF play an important role in the reproduction of C. bilbaoana coexisting with S. atrocinerea in the alkaline sediment and have the potential to stimulate or completely inhibit seed production. The community composition of native AMF and the length of the mycelium they produce spreading from roots into the surrounding soil can be determinant of the coexistence of naturally co-occurring plant species.     

Further root colonization by arbuscular mycorrhizal fungi in already mycorrhizal plants is suppressed after a critical level of root colonization

An established arbuscular mycorrhizal symbiosis suppresses further mycorrhization. It is not clear whether the observed suppressional effect is linked with the level of root colonization or not. In the present work we studied the effect of the degree of root colonization by the arbuscular mycorrhizal fungus Glomus mosseae on further root colonization by G. mosseae. At different time points barley plants grown in split-root compartments were pre-inoculated on one half of the split-root system with G. mosseae. Sequential inoculation resulted in different colonization levels. Thereafter, the second half of the split root system was inoculated. The results indicate an enhanced suppression of root colonization on the second side of the split-root system when colonization levels increased on the first side.     

Seasonal dynamics of arbuscular mycorrhizal fungi in differing wetland habitats

The dynamics and role of arbuscular mycorrhizal fungi (AMF) have been well described in terrestrial ecosystems; however, little is known about how the dynamics of AMF are related to the ecology of wetland ecosystems. The seasonal dynamics of arbuscular mycorrhizal (AM) colonization within different wetland habitats were examined in this study to determine the factors that influence AM associations and to further assess the ecological role of AMF in wetlands. Fen and marsh habitats of four wetlands in west central Ohio were sampled monthly from March to September. AMF were found at all four sites for each month sampled and were present in all of the dominant plant species. A significant effect of month (P<0.001) on AM colonization did occur and was attributable to maximum colonization levels in the spring and minimum levels in late summer. This trend existed in all four wetlands in both fen and marsh habitats, regardless of variation in water levels, percent soil moisture, or available phosphorus levels. Because abiotic factors had minimal influence on AM colonization variation and the level of AM colonization paralleled plant growth patterns, we conclude that the AM seasonal dynamic was in response to plant phenology. Our data suggest that AM associations in temperate fen and marsh habitats are prevalent in the spring during new root and vegetative growth, even for plants experiencing flooded conditions. Evidence of an overriding AM seasonal trend indicates that future studies should include a seasonal component to better assess the role and distribution of AMF in wetland ecosystems.     

Presence of arbuscular mycorrhizal fungi in South Florida native plants

The roots of 27 species of South Florida plants in 15 families (including one cycad, six palms, one Smilax, and 19 dicotyledons) native to pine rockland and tropical hardwood hammock communities were examined for arbuscular mycorrhizal fungi (AMF). These plants grow in the biologically diverse but endangered Greater Everglades habitat. Roots from field-grown and potted plants were cleared and stained. All 27 species had AMF and include 14 species having an endangered or threatened status. The Paris-type colonization occurred in two species in the families Annonaceae and Smilacaceae. The Arum-type occurred in 22 species in the families Anacardiaceae, Arecaceae (Palmae), Boraginaceae, Cactaceae (questionable), Euphorbiaceae, Fabaceae, Lauraceae, Melastomataceae, Polygalaceae, Rubiaceae, Simaroubaceae, Ulmaceae, and Zamiaceae. Three species in the families Fabaceae, Lauraceae, and Simaroubaceae had a mix of Paris- and Arum-types. The results have implications for the restoration of these endangered plant communities in the Everglades.     

Growth response ofTheobroma cacao L. seeldings to inoculation with vesicular-arbuscular mycorrhizal fungi

Summary The effects of vesicular-arbuscular mycorrhiza (VAM) on the growth and phosphorus uptake of cocoa seedlings (Theobroma cacao L.) grown for 100 days in polythene bags, were studied at five levels of phosphorus fertilization in both steamed and unsterile Bungor Series soil (a fine clayey, kaolinitic isohyperthermic Typic Paleudult). The cocoa seedlings responded well to phosphorus fertilization and mycorrhizal treatments. Plants inoculated with VAM fungi (Gigaspora spp.) gave the most vigorous growth and higher phosphorus in the leaf tissues in unsterile soil compared to plants grown in steamed soil. However, the mycorrhizal effect was significantly more pronounced (P<0.01) in plants grown in steamed than in unsterile soil. High levels of phosphorus application depressed mycorrhizal development. Phosphorus fertilizer applied at the rates of 250 and 500 ug g⁻¹ soil gave maximum root colonization and spore counts in both soil types used.     

Uptake of cadmium from an experimentally contaminated calcareous soil by arbuscular mycorrhizal maize (<Emphasis Type="Italic"> Zea mays </Emphasis>L.)

We investigated uptake of Cd by arbuscular mycorrhizal (AM) maize inoculated with Glomus mosseae from a low-P sandy calcareous soil in two glasshouse experiments. Plants grew in pots containing two compartments, one for root and hyphal growth and one for hyphal development only. Three levels of Cd (0, 25 and 100 mg kg^–1) and two of P (20 and 60 mg kg^–1) were applied separately to the two compartments to assess hyphal uptake of Cd. Neither Cd nor P addition inhibited root colonization by the AM fungus, but Cd depressed plant biomass. Mycorrhizal colonization, P addition and increasing added Cd level led to lower Cd partitioning to the shoots. Plant P uptake was enhanced by mycorrhizal colonization at all Cd levels studied. When Cd was added to the plant compartment and P to the hyphal compartment, plant biomass increased with AM colonization and the mycorrhizal effect was more pronounced with increasing Cd addition. When P was added to the plant compartment and Cd to the hyphal compartment, plant biomass was little affected by AM colonization, but shoot Cd uptake was increased by colonization at the low Cd addition rate (25 mg kg^–1) and lowered at the higher Cd rate (100 mg kg^–1) but with no difference in root Cd uptake. These effects may have been due to immobilization of Cd by the fungal mycelium or effects of the AM fungus on rhizosphere physicochemical conditions and are discussed in relation to possible phytostabilization of contaminated sites by AM plants.     

Differential influence of native and introduced arbuscular mycorrhizal fungi on growth of dominant and subordinate plants

The impact of arbuscular mycorrhizal fungi (AMF) on plant ecosystems has been intensively reported. In this research, we explored the difference between native and introduced AMF in promoting the growth of dominant and subordinate plant species. In glasshouse experiments, dominants and subordinates from subtropical grasslands were colonized by native AMF or introduced AMF, Glomus versiforme. The biomass revealed that mycorrhizal dependencies (MD) on the native AMF of the dominants were much higher than those of the subordinates, while MD on the introduced AMF changed following the replacement of native AMF with introduced AMF. A close relationship between biomass promotion and increase in phosphorus uptake was observed, indicating the important role of AMF-enhanced nutrient acquisition by roots. Our results show that plant community structures are partly determined by MD on native AMF, and could be modified by introducing exogenous AMF species.     

Response of endangered plant species to inoculation with arbuscular mycorrhizal fungi and soil bacteria

Three endangered plant species, Plantago atrata and Pulsatilla slavica, which are on the IUCN red list of plants, and Senecio umbrosus, which is extinct in the wild in Poland, were inoculated with soil microorganisms to evaluate their responsiveness to inoculation and to select the most effective microbial consortium for application in conservation projects. Individuals of these taxa were cultivated with (1) native arbuscular mycorrhizal fungi (AMF) isolated from natural habitats of the investigated species, (2) a mixture of AMF strains available in the laboratory, and (3) a combination of AMF lab strains with rhizobacteria. The plants were found to be dependent on AMF for their growth; the mycorrhizal dependency for P. atrata was 91%, S. umbrosus-95%, and P. slavica-65%. The applied inocula did not significantly differ in the stimulation of the growth of P. atrata and S. umbrosus, while in P. slavica, native AMF proved to be the less efficient. We therefore conclude that AMF application can improve the ex situ propagation of these three threatened taxa and may contribute to the success of S. umbrosus reintroduction. A multilevel analysis of chlorophyll a fluorescence transients by the JIP test permitted an in vivo evaluation of plant vitality in terms of biophysical parameters quantifying photosynthetic energy conservation, which was found to be in good agreement with the results concerning physiological parameters. Therefore, the JIP test can be used to evaluate the influence of AMF on endangered plants, with the additional advantage of being applicable in monitoring in a noninvasive way the acclimatization of reintroduced species in nature.     

Mycotrophy of crops in rotation and soil amendment with peat influence the abundance and effectiveness of indigenous arbuscular mycorrhizal fungi in field soil

Mycotrophy of previous crops has been shown to have an impact on arbuscular mycorrhizal fungi (AMF), and the growth and productivity of succeeding crops. We studied the impact of 3 years of cultivation of eight crops with different degrees of mycotrophy, including mycorrhizal (strawberry, rye, timothy, onion, caraway) and non-mycorrhizal (turnip rape, buckwheat, fiddleneck) hosts, as well as the impact of peat amendment, on the effectiveness, amount and diversity of indigenous AMF. A field experiment having a split-plot design with peat amendment as the main plot, crop cultivation as a sub-plot and three replications, was carried out on silt clay mineral soil in 1999–2001. A well-humified dark peat was applied immediately before establishment of the field experiment. Each year, the relative mycorrhizal effectiveness of soil collected in September, in terms of shoot dry weight (RME_DW), was determined in a bioassay. In the 3rd year of the experiment, AMF spores were also extracted and identified from the field soil. Expressed as the mean of 3 years of cropping in unamended soil, the mycorrhizal crops strawberry and caraway maintained RME_DW most effectively, while the values were lower in the non-host crops buckwheat, turnip rape and fiddleneck. In addition, the numbers of AM spores detected in soil were considerably greater during 3 years of strawberry cultivation. In soil under caraway, there were high numbers of AM spores compared to the other crops. In soil amended with peat, the situation was in some cases opposite of that of unamended soil; RME_DW was highest in rye and onion and lowest in strawberry and caraway. The reasons behind the negative impact of peat on mycorrhizal effectiveness in strawberry soil may be due to the microbiological properties of peat. The importance of including mycotrophic species in crop rotations for maintaining high soil quality and for increasing yields of subsequent crops is discussed.     

Determination of the nitrogen source for arbuscular mycorrhizal fungi by 15N application to soil and plants

The source of nitrogen in the spores of arbuscular mycorrhizal (AM) fungi was quantified by a ¹⁵N-labeling technique. N was applied as coated urea to the soil and in solution to plant shoots. Soil-applied fertilizer had a significant effect on spore % ¹⁵N (P<0.01), with a 24–75% contribution to spore N. Fertilizer applied to either alfalfa shoots or bahia grass shoots had little effect on spore % ¹⁵N, accounting for 0–14% or 1–9% of spore N, respectively. These results indicate that AM fungi obtain spore N mostly from the soil. The small amount of spore N originating from shoot-applied N may have been obtained via root exudation. Accepted: 6 November 2000