Seasonality of mycorrhizae in coastal sand dunes of Baja California

 Populations of arbuscular mycorrhizal fungi were estimated from spores associated with seven plant species in coastal dunes at El Socorro, near Ensenada, Baja California, during six months in 1992. The seasonal patterns of percent root colonization were also described in the same species during the wet season (January–March) and the dry season (April–July). Comparisons were made between the pioneer species (Abronia maritima) in the mobile dunes and six species (Abronia umbellata, Atriplex julacea, Camissonia californica, Haplopappus venetus, Helianthus niveus and Lotus spp.) in the fixed dunes. Mycorrhizal colonization in Abronia maritima was slight (<1%) and we observed few spores (<1/g soil). All of the species in the fixed dune formed mycorrhizae with up to 80% colonization in early summer, and no more than 4 spores/g soil by late summer. The highest percentages of total colonization and abundance of spores did not coincide temporally for any of the seven species, but the percentages were higher in summer than in spring. Arbuscules were more abundant when the soil was moist, and vesicles more abundant when it was dry. Accepted: 16 August 1995     

Abundance of arbuscular mycorrhizal fungi spores in different environments in a tropical rain forest, Veracruz, Mexico

 The aim of this study was to compare mycorrhizal abundance and diversity in sites with different regimes of disturbance in a tropical rain forest at Los Tuxtlas, Veracruz, Mexico. Arbuscular mycorrhizal spores were quantified at two sites: closed canopy and gaps in the forest. Data were recorded during dry, rainy, and windy ("nortes") seasons. Spores of eight Glomus species, sporocarps of three Sclerocystis species, three species of Acaulospora and two of Gigaspora were found. Significant differences in the number of species and spores were found among seasons. The highest numbers of species and spores were observed during the dry season, with a marked decrease during the rainy season. Our results show that disturbance does not but seasonality does affect abundance and richness of mycorrhizal spores in this tropical wet forest. Accepted: 11 October 1998     

Effect of vesicular-arbuscular mycorrhizae on seedling growth of four tree species from the tropical deciduous forest in Mexico

The influence of vesicular-arbuscular mycorrhizae on the growth of seedlings of Caesalpinia eriostachys, Cordia alliodora, Ipomoea wolcottiana and Pithecellobium mangense was investigated in a greenhouse experiment conducted at the Biological Station of Chamela on the Pacific coast of Mexico. Dry biomass production, relative growth rate, root/shoot ratio and mycorrhizal dependency were quantified for 75-day-old seedlings. With the exception of the pioneer species I. wolcottiana, mycorrhizal infection resulted in increases in biomass production, relative growth rate and leaf area. The root/shoot ratios attained for the species, however, did not show a consistent trend with infection. Nevertheless, all species had root/shoot ratios below 1 with infection and only one, Cordia alliodora, had a ratio greater than 1 without infection. The two late successional species from the mature part of the forest, Caesalpinia eriostachys and P. mangense, showed a larger mycorrhizal dependency than the two associated with disturbed environments.     

Arbuscular mycorrhizal inoculation and superphosphate application influence plant development and yield of coffee in Brazil

 This paper reports a 6-year field study of the effects of mycorrhizal pre-colonization of coffee seedlings on initial crop development and coffee bean yield in a low-fertility Oxisol amended with superphosphate (P) at planting. The experiment included five P rates (0, 20, 40, 80 and 160 g plant^–1 P₂O₅) combined with seven fungal treatments [non-mycorrhizal control, pre-colonization with a mix of Glomus clarum and Gigaspora margarita (CM) and with five isolates of Glomus etunicatum]. Inoculated and non-inoculated outplants were raised under glasshouse conditions, transplanted into the field in January 1989 and monitored until July 1995. Plant height and stem diameter were greatly enhanced by P application and were higher in mycorrhizal seedlings than in controls up to 19 months after transplanting (MAT) but were not different at 26 MAT. Inoculation effects on tree canopy diameter were significant up to 26 MAT, at which time mycorrhizal colonization was high (43–55%), but did not differ amongst plants, regardless of whether or not the plants had been pre-colonized at the nursery stage. Root colonization and spore number in the soil were reduced by high P rates at 26 MAT. The first bean yield (1991) was highly enhanced by P and all pre-colonization treatments (38% increment over control) and these factors showed a significant interaction. Three isolates of G. etunicatum showed yield enhancements above 50%. The P rate for maximal yield was 207 g plant^–1 P₂O₅ for non-pre-colonized and approximately 100 g plant^–1 for pre-colonized plants. For this harvest, the mycorrhizal biofertilizer effect was equal to 254 kg ha^–1 P₂O₅. In subsequent years, pre-colonization effects were reduced and inconsistent. In 1992, 1993 and 1995, yield was affected by P but not by mycorrhizal inoculation. In 1994 there was a P versus mycorrhiza interaction and CM and G. etunicatum-Var gave higher yields than non-precolonized plants. Considering accumulated yield for this 5-year period, P application resulted in high yield increment in all treatments, whereas pre-colonization effects were extremely diminished. However, despite inconsistency amongst mycorrhizal treatments, pre-colonization effects were detected at the fifth harvest in some fungal treatments. Based on the total yield of five harvests, maximal productivity was achieved with CM at 20 g plant^–1 P₂O₅ and with CM and G. etunicatum-Var at the highest P rate. Diminishing mycorrhizal effects over time are related to colonization of non-precolonized seedlings by the indigenous fungi and to the reduced external P requirement of the mature crop. If adequate phosphorus is applied at planting, pre-colonization of outplants with selected arbuscular mycorrhizal fungi enhances early crop development and productivity of coffee in low-fertility soils of Brazil. Accepted: 3 October 1997     

Arbuscular mycorrhizal colonization of halophytes in Central European salt marshes

 Halophytes from both coastal and inland Central European salt marshes were examined for colonization by arbuscular mycorrhizal (AM) fungi. Plants from different families were strongly colonized but the degree of colonization varied with the individual plant and apparently during the vegetation period, too. Members of the typical non-mycorrhizal families like Armeria maritima of the Plumbaginaceae and Salicornia europaea of the Chenopodiaceae were found to be colonized, particularly in the drier salt marshes. High numbers of Glomus spores were found in the saline soils, especially those of the inland locations examined. Approximately 80% of these spores were from Glomus geosporum as shown by a typical restriction fragment length polymorphism (RFLP) pattern of the amplified internal transcribed spacer regions. The present study demonstrates that RFLP analysis is useful when screening habitats for the occurrence of mycorrhizal fungi which can be identified only with difficulty by morphological criteria. Accepted: 25 August 2000     

Rapid detection of arbuscular mycorrhizae in roots and soil of an intensively managed turfgrass system by PCR amplification of small subunit rDNA

 Arbuscular mycorrhizal fungi (AMF) were detected in uninoculated soil and roots of turfgrass (Agrostis palustris) by direct extraction and PCR amplification of the small subunit rRNA gene. Sequence analysis of the cloned PCR product confirmed the identity of the amplified DNA as an AMF sequence having 95% identity to Glomus intraradices. The sensitivity of the method was gauged by comparison with the most probable number analysis of infective propagules in an intensively managed turfgrass system having 56 propagules per 100 g soil. In contrast to the heavily managed system, infective propagule numbers were high in systems under moderate and limited management. The method described may be useful for rapid investigations of genetic diversity and community structure of AMF. Accepted: 8 January 1999     

菌根技术在沙地植被恢复中的研究

库布齐沙地植被恢复中的菌根技术研究 ,注重于因地制宜、适菌适技。对此 ,利用当地A、B两种沙壤条件并对其作加入草炭和不加入草炭条件处理 ,选用适合当地造林树种油松、樟子松进行室内模拟实验及野外实地小型造林试验 ,菌剂以单菌剂、组合菌剂方式实施。室内模拟试验结果表明 ,单菌剂对油松幼苗作用效果为 :Cr >Ra >Li>Hm。双组合菌剂Ra Li、Hm Li和Ra Cr接种的幼苗对草炭的依赖性不强。选择出Cr和Ra菌根菌剂为沙地植被恢复较为适合的菌剂。油松和樟子松两树种无论施单菌剂或双组合菌剂 ,油松幼苗长势均优于樟子松幼苗。造林试验结果表明 ,在同一块样地菌剂处理 ,三合一优于二合一菌剂组合。接种菌根菌剂幼苗地上生物量高于施入复混肥的幼苗。不同样地菌剂处理的幼苗成活率在个别菌剂组合中低于复混肥。因个别菌剂培养周期不足而致使其菌丝体与基质发酵不完全 ,而遇到造林基地干旱 ,土壤温度升高 ,导致基质仍再发酵、腐熟 ,这就使部分生长较弱的幼苗受到了伤害 ,因而幼苗成活率低。     

Dew and its effect on two heliophile understorey species of a tropical dry deciduous forest in Mexico

 A series of horizontal and vertical measurements of dew deposition and dew duration were carried out in a tropical dry deciduous forest in western Mexico (19° 30′ N, 105° 03′ W). The effect of dew on transpiration in heliophile species was also investigated. The amount of dew was very variable with no temporal or spatial pattern. The amount of dew measured at two horizontal transects (maximum and minimum) (at heights of 0.20 m and 1.30 m above ground level) was from 0.014 to 0.203 mm and from 0.013 to 0.061 mm in the middle and at the end of the dry season, respectively. Dew deposition at different vertical levels (0.50–12.5 m height) ranged from 0.04 to 0.36 mm. The duration of dew formation ranged between 60 and 129 min after sunrise above the canopy (a height of 11 m), and between 259 and 290 min after sunrise at a height of 2 m. Daily transpiration rates were 883 and 632 g m^–2 d^–1 in Coccoloba liebmannii and 538 and 864 g m^–2 d^–1 in Jacquinia pungens in January and April, respectively. Transpiration was restricted from sunrise to early afternoon in April, as a result of the pronounced midday closure of stomata in both species. The reduction of transpiration by dew ranged from 13.2 to 50.1 g m^–2 d^–1 and from 4.5 to 77.7 g m^–2 d^–1 for C. liebmannii and J. pungens, respectively. Dew can play an important role in enhancing the survival of heliophile species in the dry season by reducing transpiration rates during the morning. Received: 30 April 1998 / Accepted: 14 December 1998     

The use of arbuscular mycorrhizae to control onion white rot (Sclerotium cepivorum Berk.) under field conditions

 A field experiment was carried out to determine the effects of the inoculation of onion (Allium cepa L.) with Glomus sp. Zac-19 on the development of onion white rot (Sclerotium cepivorum Berk.) and on onion production. Mycorrhization delayed onion white rot epidemics by 2 weeks and provided a significant protection against the disease for 11 weeks after onion transplanting, as compared with nonmycorrhizal controls. Mycorrhizal plants showed an increase of 22% in yield, regardless of the presence of the white rot pathogen. Accepted: 8 January 1996     

Mycorrhizae in Adenostoma fasciculatum Hook. & Arn.: a combination of unusual ecto- and endo-forms

 The mycorrhizal status of Adenostoma fasciculatum, the dominant shrub in California chaparral, has been unclear. In two typical, nearly monospecificstands, A. fasciculatum was found to have arbuscules and intercellular hyphae. Antisera detected hyphae of the arbuscular mycorrhizal (AM) fungal genera Acaulospora, Glomus, and Scutellospora, although we found only spores of Glomus. Some roots had partial sheaths and inter- and intracellular septate fungi without indications of root necrosis. Ectomycorrhizal root tips were also found, including Cenococcum and other unknown taxa. Sporocarps of EM fungi including species of Rhizopogon, Pisolithus, Balsamia, Laccaria, Hygrophorus, and Cortinarius were found in the stand, with no other EM or arbutoid mycorrhizal plants nearby. These observations indicate that A. fasciculatum forms mycorrhizae with AM, septate, and EM fungi, but often fails to form easily recognizable mycorrhizal structures. Accepted: 5 September 1998     

Effect of forest fire on number, viability and post-fire re-establishment of arbuscular mycorrhizae

 Forest fire can affect arbuscular mycorrhizal (AM) fungi by changing the soil conditions and by directly altering AM proliferation. We studied the effects of a severe forest fire at Margalla Hills near Islamabad on the number and viability of AM fungal propagules in the burnt soil and their role in the re-establishment of post-fire infection in colonized plants. Compared with a nearby control area, the burnt site had a similar number of total spores but a lower number of viable AM fungal propagules. The roots of the two most frequent species at the burnt site, Dodonaea viscosa and Aristida adscensionis, showed a gradual increase in percentage root length colonized by AM fungi in general and hyphal infection in particular. Our results indicate resumption of mycorrhizal activity following the fire, probably from AM hyphae in the roots of these dominant shrubs. Accepted: 18 July 1997     

Effects of inoculation of phosphate-solubilizing microorganisms and an arbuscular mycorrhizal fungus on mungbean grown under natural soil conditions

 The effect of inoculation of the phosphate-solubilizing microorganisms (PSM) Bacillus circulans and Cladosporium herbarum and the arbuscular mycorrhizal (AM) fungus Glomus fasciculatum with or without Mussoorie rockphosphate (MRP) was studied in a P-deficient natural non-disinfected sandy soil on mungbean (Vigna radiata). The AM levels increased following the addition of MRP or inoculation with PSM or G. fasciculatum. Both grain and straw yield of mungbean increased following inoculation with PSM or the AM fungus. In general, the increase in yield was higher in the presence of MRP and inoculation with a combination of PSM and AM fungus. Highest N and P uptake by mungbean was recorded after treatment with a combination of B. circulans, C. herbarum and G. fasciculatum in the presence of MRP. Generally the PSM population increased after AM fungus inoculation. Accepted: 13 October 1997     

Arbuscular mycorrhizal colonization of lime in different agroecosystems of the dry tropics

 Tecomán, in the Mexican state of Colima, had the world's greatest production of lime Citrus aurantifolia Swingle. Typical farming systems in the area include: (a) high-input monoculture, (b) a high-input system in which lime trees grow together with coconut palms, (c) a low-input system called "Family Farms" or "Family Gardens". In the Family Gardens, cultural practices are minimal and other fruit trees (about 16 species) coexist with the lime trees. This traditional minimal input system makes use of locally available resources and they are structurally very diverse. Arbuscular mycorrhizae may be crucial for sustainable production in Family Gardens. Root colonization and spore populations of fungi were scored at 2-week intervals in the three agroecosystems during a 6-month period. First samples were taken after the application of chemical fertilizer and irrigation in the high-input systems. Root colonization of lime was much higher and consistent in the low-input plots than in conventionally farmed plots, with colonization levels of 50–62% that remained the same throughout the sampling time; the high-input systems showed a high variation and lower level of colonization, 36% and 27% in associated and monoculture systems, respectively. Spore abundance was higher in the high-input systems but showed constant variation. The results suggest a strong effect of agroecosystem on mycorrhizal colonization of lime roots. Accepted: 12 September 1995     

Coinoculation efficacy of ectomycorrhizal fungi on Pinus patula seedlings in a nursery

 The coinoculation efficacy of the ectomycorrhizal fungi Laccaria laccata and Thelephora terrestris on the growth and mycorrhizal development of Pinus patula seedlings was studied and compared to individual inoculation of these fungi in a nursery. The total number of mycorrhizas was higher in seedlings inoculated with the combined inoculum than with the individual inocula. The colonization by T. terrestris was higher than L. laccata when the seedlings were inoculated with the two fungi simultaneously. Coinoculation significantly increased the height and dry weight of the seedlings compared with individual inoculation, both in steam-sterilized and unsterilized soil. Accepted: 12 May 1997     

Evaluation of commercial arbuscular mycorrhizal inocula in a sand/peat medium

Eight commercial inocula of arbuscular mycorrhizal fungi (AMF) were tested for their ability to colonize plant roots in the sand/peat medium specified by the U.S. Golf Association for use in putting greens. Using the standard assay for potency of inocula (Zea mays grown for 6 weeks in containers), inocula were added at the rate recommended by the manufacturer as well as at five and ten times the recommended rate. To ensure that growth conditions were conducive to AM formation, a soil-based inoculum of native AMF also was assessed for inoculum potential. Only three of the commercial inocula formed mycorrhizas when used at the recommended rate, and the extent of colonization ranged from 0.4 to 8%. Increasing the amount of inoculum resulted in colonization levels of 8.6 to 72.5% at the highest rate (10×). Mean colonization using the native AMF was 60%. One inoculum that did not form mycorrhizas at the recommended rate or at 5× produced 8.6% colonization at 10×. An inoculum that did not produce mycorrhizas at any application rate did contain a fungus tentatively identified as a root pathogen (Olpidium brassicae) that colonized the corn roots. The failure of five of the eight commercial inocula to colonize roots when applied at the recommended rate suggests that preliminary trials should be made before commercial AMF inocula are used in important plantings.     

High richness of ectomycorrhizal fungi and low host specificity in a coastal sand dune ecosystem revealed by network analysis

Ectomycorrhizal (EM) fungi are ubiquitous in temperate and boreal forests, comprising over 20,000 species forming root symbiotic associations with Pinaceae and woody angiosperms. As much as 100 different EM fungal species can coexist and interact with the same tree species, forming complex multispecies networks in soils. The degree of host specificity and structural properties of these interaction networks (e.g., nestedness and modularity) may influence plant and fungal community assembly and species coexistence, yet their structure has been little studied in northern coniferous forests, where trees depend on EM fungi for nutrient acquisition. We used high‐throughput sequencing to characterize the composition and diversity of bulk soil and root‐associated fungal communities in four co‐occurring Pinaceae in a relic foredune plain located at Îles de la Madeleine, Québec, Canada. We found high EM fungal richness across the four hosts, with a total of 200 EM operational taxonomic units (OTUs), mainly belonging to the Agaricomycetes. Network analysis revealed an antinested pattern in both bulk soil and roots EM fungal communities. However, there was no detectable modularity (i.e., subgroups of interacting species) in the interaction networks, indicating a low level of specificity in these EM associations. In addition, there were no differences in EM fungal OTU richness or community structure among the four tree species. Limited shared resources and competitive exclusion typically restrict the number of taxa coexisting within the same niche. As such, our finding of high EM fungal richness and low host specificity highlights the need for further studies to determine the mechanisms enabling such a large number of EM fungal species to coexist locally on the same hosts.     

Spatial patterns of mycorrhizal infectiveness of soils long a successional chronosequence

 This study quantified intersite variation and spatial pattern in arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) infectivity of soils among six sites constituting a successional chronosequence in southwestern Ohio, USA. The study sites included an active agricultural field (chronic disturbance), a site which had been stripped of its surface soil (pseudo-stripmine, acute disturbance), 5- and 10-year-old fields, a 25- to 30-year-old prairie restoration, and an undisturbed, mature forest. AM infectivity was lower in the agricultural field, successional fields, and prairie than in the mature forest, but there was no clear correlation between time since disturbance and the overall level of AM infectivity. Spatial structure in AM infectivity decreased with time since disturbance. In the pseudo-stripmine site and active soybean field, semivariance analysis attributed 44–50% of the total variance in AM infectivity among samples to spatial structure, whereas spatial dependancy accounted for only 18% of total variance in the mature forest. Kriging of AM infectiveness demonstrated small, isolated areas in the disturbed plots that were devoid of AM infectiveness, whereas the kriged AM maps of the other four sites showed AM infectiveness to become progressively more homogeneous. ECM infectiveness was lacking from 35–50% of the samples from the disturbed sites, and both overall ECM infectiveness and ECM diversity increased with time since disturbance. Approximately 44% of the variance in ECM infectiveness was related to spatial structure in the two disturbed sites, and large areas entirely devoid of ECM infectivity were present on the kriged ECM maps for these sites. There was less spatial structure in ECM in the old fields and prairie and very little in the mature forest. The results of this study emphasize the need to explicitly evaluate spatial heterogeneity in mycorrhizal infectivity in studies of the role of mycorrhizae in succession. Accepted: 4 August 1995     

Coinoculation of containerized Douglas-fir (Pseudotsuga menziesii) and maritime pine (Pinus pinaster) seedlings with the ectomycorrhizal fungi Laccaria bicolor and Rhizopogon spp.

 Coinoculations with mycelium of Laccaria bicolor and spores of Rhizopogon spp. included in alginate gel have been carried out to determine: (1) the ability of the mixed inoculum to produce dual-colonized containerized Douglas-fir and maritime pine planting stocks and (2) the colonization pattern of the two fungi in individual root systems. For both tree species, the maximal proportion of dual-colonized seedlings obtained almost never exceeded 50%. The rest of the seedlings remained colonized by a single fungus or were non-colonized. In Douglas-fir inoculations, the relationship between the dual-colonized seedlings obtained and the initial dose of the two fungi was highly significant. The highest proportion of dual-colonized seedlings was obtained when the highest dose of R. subareolatus was used (10⁶ spores/seedling), regardless of the dose of L. bicolor. Among the treatments producing 25% or more dual-colonized seedlings, differences in the proportion of Laccaria/Rhizopogon mycorrhizas and total root colonization percentages were not clearly related to the initial combination of doses. The proportion of dual-colonized maritime pine seedlings was not significantly related to the initial inoculation doses of the two fungi. The proportion of Laccaria/Rhizopogon mycorrhizas was not significantly different among treatments with 25% or more dual-colonized seedlings, whereas total colonization percentages ranged from 37% with the combination 0.08/10⁴ (g L. bicolor / spores R. roseolus per seedling) to 74% with the combination 0.08/10⁶, this difference being statistically significant. Accepted: 15 September 1998