VAM association in the shrub Myrica cerifera on a Virginia,USA barrier island

A combined laboratory and field study examined the potential for a symbiotic association between the actinorhizal shrub Myrica cerifera and vesicular arbuscular mycorrhizal (VAM) fungi on a Virginia barrier island. M. cerifera seedlings and two test species, Zea mays and Strophostyles umbellata, were grown in an environmental chamber on soils collected from four sites differing in soil age (< 5 to over 130 years), salinity (1–35 g/g total soil chloride), and edaphic characteristics. Seedling root infection was significantly lower for all three species in the youngest soils from the beach where salinity was highest. Stained M. cerifera roots revealed all the components for a functional VAM association; however, there were significantly fewer arbuscules and vesicles relative to the test species. Among field-collected M. cerifera, infection was not detected in mature shrubs from the bay side of the island, where M. cerifera thickets were in a state of degeneration. Infection was highest in soils from the young, developing thickets, and in the most stable thickets of the island interior. Despite the dynamic nature of the barrier island environment, VAM associations with M. cerifera appear to be present, especially in seedlings and developing shrub thickets.     

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.     

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.     

The role of VAM fungi in nitrogen dynamics in maize-bean intercrops

Nitrogen (N) transfer from N-fixing legumes via vesicular-arbuscular mycorrhizal (VAM) fungi to associated non-fixing plants has been demonstrated in greenhouse experiments. To date, this transfer has been shown only where mineral N is applied shortly before harvest, and hence is readily available. We have yet to demonstrate VAM-mediated N transfer where soil-N is limiting, a condition under which most traditional legume-nonlegume intercrops are grown.In this study, ¹⁵N-enriched soil (with 0.28%N) was used to distinguish between the uptake of soil- and atmospherically-derived N in maize grown with beans in the presence or absence of VAM fungi. VAM infection did not result in transfer of fixed N or soil N from bean to maize, despite a VAM-stimulated increase in N fixation in bean. In fact, beans were more competitive for soil N when mycorrhizal. N content in beans increased by 75% with a concomitant 22% decrease in mg N per maize plant. The competitive effect may have resulted from a VAM-mediated shift in carbon allocation in beans (but not maize) from shoots to roots.     

Effect of tillage and farming system upon VAM fungus populations and mycorrhizas and nutrient uptake of maize

Low-input agricultural systems that do not rely on fertilizers may be more dependent on vesicular-arbuscular mycorrhizal [VAM] fungi than conventionally managed systems. We studied populations of spores of VAM fungi, mycorrhiza formation and nutrient utilization of maize (Zea mays L.) grown in moldboard plowed, chisel-disked or no-tilled soil under conventional and low-input agricultural systems. Maize shoots and roots were collected at four growth stages. Soils under low-input management had higher VAM fungus spore populations than soils under conventional management. Spore populations and colonization of maize roots by VAM fungi were higher in no-tilled than in moldboard plowed or chisel-disked soil. The inoculum potential of soil collected in the autumn was greater for no-till and chisel-disked soils than for moldboard plowed soils and greater for low-input than conventionally farmed soil. The effects of tillage and farming system on N uptake and utilization varied with growth stage of the maize plants. The effect of farming system on P use efficiency was significant at the vegetative stages only, with higher efficiencies in plants under low-input management. The effect of tillage was consistent through all growth stages, with higher P use efficiencies in plants under moldboard plow and chisel-disk than under no-till. Plants grown in no-tilled soils had the highest shoot P concentrations throughout the experiment. This benefit of enhanced VAM fungus colonization, particularly in the low-input system in the absence of effective weed control and with likely lower soil temperatures, did not translate into enhanced growth and yield.     

Influence of temperature on colonization of spring barleys by vesicular arbuscular mycorrhizal fungi

The effects of three soil temperatures on growth of spring barleys (Hordeum vulgare L.) and on their root colonization by vesicular arbuscular mycorrhizal (VAM) fungi from agricultural soils in Montana (USA) or Syria at different inoculum concentrations were tested in soil incubators in the greenhouse. The number of mycorrhizal plants as well as the proportion and intensity of roots colonized increased with higher soil temperatures. VAM fungi from Montana, primarily Glomus macrocarpum, were cold tolerant at 11°C while those from Syria, primarily G. hoi, were heat tolerant at 26°C. Inoculum potential of Montana VAM fungi was higher than Syrian VAM fungi in cool soils. Harmal, selected from Syrian barley land races, had the highest colonization by mycorrhizal fungi of the cultivars tested.Journal Series Paper: J-2532 Montana Agricultural Experiment Station.     

Topsoil storage effects on primary production and rates of vesicular-arbuscular mycorrhizal development inAgropyron trachycaulum

Summary A greenhouse study was conducted to determine the effects of stockpiling prairie grassland topsoil for 3 years on mycorrhizal development and root and shoot production of slender wheatgrass. The vesicular-arbuscular mycorrhizal (VAM) fungi involved in the symbiosis were also assessed as was the decomposition potential of the soil. During the first week of growth, VAM development in grasses grown in the stockpiled soil lagged behind that observed for grasses in the undisturbed soil. However, by 3 weeks, the mycorrhizal infection in plants in the stockpiled soil had reached levels similar to that in plants in the undisturbed soil. The dominant species of VAM fungi involved in the symbiosis at 8 weeks after planting shifted fromGlomus fasciculatum in the undisturbed soil toG. mosseae in the stockpiled soil. The delay in initial VAM infection and shift in VAM fungal species did not significantly affect plant productivity which was greatest in the stockpiled soil. The greater shoot production exhibited by grasses in the stockpiled soil was attributed to higher levels of NO₃-N in the stockpiled than undisturbed soil. The potential of the soil to decay dead slender wheatgrass roots was not altered by stockpiling.     

Positive correlation between VAM-induced changes in root exudation and mycorrhizosphere mycoflora

The influence of vesicular-arbuscular mycorrhizal (VAM) fungi on rhizosphere mycoflora was studied together with the possible mechanism involved in this process. Six combinations of VAM fungi and phosphorus fertilizer treatments were applied to Leucaena leucocephala roots and quantitative and qualitative observations were made periodically of the rhizosphere mycoflora and constituents of root exudates. The results obtained indicate that the presence of specific mycoflora in the rhizosphere of mycrorrhizal roots is mediated through root exudates rather than being an outcome of improved P nutrition.     

Positive association between mycorrhiza and foliar endophytes in Poa bonariensis, a native grass

The interaction between mycorrhiza and leaf endophytes (Neotyphodium sp.) was studied in three Poa bonariensis populations, a native grass, differing significantly in endophyte infection. The association between endophytes and mycorrhizal fungi colonisation was assessed by analysing plant roots collected from the field. We found that roots from endophyte-infected populations showed a significantly higher frequency of colonisation by mycorrhizal fungi and that soil parameters were not related to endophyte infection or mycorrhiza colonization. In addition, we did not observe significant differences in the number of AM propagules in soils of the three populations sites. We also report the simultaneous development of Paris-type and Arum-type mycorrhiza morphology within the same root systems of P. bonariensis. The co-occurrence of both colonisation types in one and the same root system found in the three populations, which differed in Neotyphodium infection, suggests that foliar endophytes do not determine AM morphology. The percentage of root length colonised by different types of fungal structures (coils, arbuscules, longitudinal hyphae and vesicles) showed significant and positive differences in arbuscular frequency associated with endophyte infection, whereas the much smaller amounts of vesicles and hyphal coils did not differ significantly.     

Vesicular-arbuscular mycorrhizal effectiveness in an acid soil amended with fresh organic matter

A greenhouse investigation was undertaken to determine the influence of fresh organic matter on the formation and functioning of vesicular-arbuscular mycorrhizal symbiosis in Leucaena leucocephala grown in an acid aluminum-rich ultisol. In soil not amended with fresh organic matter or lime, plants failed to grow. Mycorrhizal infection level, mycorrhizal effectiveness measured in terms of pinnule P content of L. leucocephala leaves and dry matter yield of the legume increased with increase in fresh organic matter. Although VAM colonization level and dry matter yield of L. leucocephala were significantly higher if the test soil was limed (7.2 cmole OH^–) than if amended with fresh organic matter, the latter was as effective as lime in off-setting the detrimental effect of aluminum on mycorrhizal effectiveness. The lower mycorrhizal colonization level and the lower dry matter yield noted in the soil treated with fresh organic matter appears to be related to the inadequacy of Ca in the soil amended with fresh organic matter. These observations are supported by the low calcium status of soil and plant tissues in the absence of lime. It is concluded that while fresh organic matter, in appropriate amounts, could protect sensitive plants and VAM symbiosis against Al toxicity in acid soils, maximum mycorrhizal inoculation effects are not likely to be attained unless the soils are also amended with Ca.Contribution from Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No 3740.     

Dual axenic culture of sheared-root inocula of vesicular-arbuscular mycorrhizal fungi associated with tomato roots

Surface-sterilized sheared-root inocula of two vesicular-arbuscular mycorrhizal (VAM) fungi (Glomus intraradices and G. versiforme) from pot cultures associated with excised tomato roots showed significant sporulation and the production of an extensive hyphal biomass. As many as 10²–10³ axenic mature spores were recovered in Petri dishes during 3 months incubation in the dark. Propagules of both species were able to complete their vegetative life cycle in vitro and efficiently colonize Acacia albida roots after 1 month under greenhouse conditions. The effectiveness of 0.5 cm pieces of VAM roots as starter inocula indicates the high inoculum potential of intravesicle propagules.     

Cultivar variation in the effect of chlorsulfuron in depressing the uptake of copper in wheat

The application of herbicides has induced symptoms of nutrient deficiencies under some circumstances. This glasshouse study examined the effect of chlorsulfuron on the uptake and utilization of copper (Cu) in four cultivars of wheat plants (Triticum aestivum L. cvs. Kulin, Cranbrook, Gamenya and Bodallin) on a Cu-responsive soil. Application of chlorsulfuron depressed the concentration of Cu in wheat plants receiving either inadequate or adequate Cu. In plants with inadequate Cu supply, chlorsulfuron increased the severity of Cu deficiency. Shoot weight was markedly decreased by chlorsulfuron at all levels of Cu, through decreasing the number of tillers and the elongation of leaves. This decreased growth of shoots occurred prior to the effect on Cu concentration in tissues. The retranslocation of Cu in old tissues over time was unaffected by chlorsulfuron. In all wheat cultivars, the decreased growth of shoots were correlated with the concentration of Cu in the youngest fully emerged leaf blade with critical levels of 1.6−1.7 at day 25 and 0.9−1.0 μg g⁻¹ d. wt. at day 60. The application of chlorsulfuron tended to increase the critical level at day 25 but not at day 60. In addition, Kulin seems to be most, and Cranbrook least, sensitive to chlorsulfuron. This sensitivity was associated with the sensitivity of the cultivars to Cu deficiency. It is suggested that chlorsulfuron application induces Cu deficiency in wheat plants mainly due to effects on the uptake of Cu. This revised version was published online in June 2006 with corrections to the Cover Date.     

Infection by the VA-mycorrhizal fungusGlomus caledonium inHedysarum coronarium as influenced by host plant and P content of soil

The low degree of infection ofHedysarum coronarium L. (sulla) exposed to inoculum of the VAM endophyteGlomus caledonium was investigated. Infection began after a prolonged lag phase and remained at very low levels even after three months’ growth. Neither very high rates of inoculum, nor very low P content of the soil raised the low infection level of the sulla plants. There appeared to be some differences in rate of infection among ten different ecotypes of sulla but the level of infection remained low in all cases. In all tested populations some plants remained uninfected. The low infection rate of sulla may therefore have a genetic basis. It was shown that the growth ofH. coronarium is hardly improved by phosphate fertilization. This may explain the poor response of this plant species, adapted to grow in nutrient-deficient soil, to VAM. Programmes aimed at increasing the productivity in marginal soils through the introduction of efficient VAM endophytes should take into account the fact that certain plant species growing in marginal soils may not always benefit from mycorrhizal inoculation, due to their inherently low mycorrhizal dependency.     

Influence of colonisation by an arbuscular mycorrhizal fungus on the growth of seedlings of<Emphasis Type="Italic"> Banksia ericifolia</Emphasis> (Proteaceae)

Tap and primary lateral roots of seedlings of the putatively non-mycorrhizal Banksia ericifolia became marginally colonised when grown in an established mycelium of an arbuscular mycorrhizal (AM) fungus in the laboratory. A similar degree of colonisation was found in seedlings from an open woodland. All colonies lacked arbuscules. Two factors influencing colonisation and associated growth of host plants were examined experimentally: concentration of P in the soil and organic energy associated with the fungus. While some inoculated seedlings were slightly smaller when colonised by AM fungi, the results were inconsistent and never statistically significant. Seedlings take up insignificant quantities of soil P during early growth, even in the presence of abundant added P. Though colonisation was minor in all cases, an existing mycelium, whether or not connected to a companion plant, slightly increased the amount of root of B. ericifolia colonised by an AM fungus. All seedlings grew slowly. Shoots were significantly larger than roots, until the initiation of proteoid roots which commenced at about 40 days after germination, with both relatively high and low P supply.     

Effects of P-fertilization and inoculation by two vesicular-arbuscular mycorrhizal fungi on growth and nodulation ofCalopogonium caeruleum

The growth response ofCalopogonium caeruleum, a leguminous covercrop in plantation agriculture, to inoculation with two vesicular-arbuscular mycorrhizal (VAM) fungi was investigated in five phosphorus (P)-deficient soils supplied with various levels of rock phosphate. Significant shoot yield increases over the uninoculated controls were obtained in most sterilised or unsterilised soils at all applied P levels, although the inoculant VAM fungi differed in their effectiveness in the soils used. Responses in mycorrhizal root infections, P and nitrogen (N) concentrations in tops and plant nodulation varied. The results are discussed in relation to the edaphic environment of the mycorrhizal association.     

Mycorrhizal infection,phosphorus uptake,and phenology in Ranunculus adoneus: implications for the functioning of mycorrhizae in alpine systems

Phosphorus levels, phenology of roots and shoots, and development of vesicular arbuscular mycorrhizal (VAM) fungi were monitored for two years in natural populations of the perennial alpine herb, Ranunculus adoneus. The purpose of this study was to understand how phosphorus uptake relates to the phenology of R. adoneus and to ascertain whether arbusculus, fungal structures used for nutrient transfer, were present when maximum phosphorus accumulation was occurring. Arbuscules were only present for a few weeks during the growing season of R. adoneus and their presence corresponded with increased phosphorus accumulation in both the roots and shoots of R. adoneus. In addition, phosphorus accumulation and peaks in mycorrhizal development occurred well after plant reproduction and most plant growth had occurred. The late season accumulation of phosphorus by mycorrhizal roots of R. adoneus is stored for use during early season growth and flowering the following spring. In this way R. adoneus can flower before soils thaw and root or mycorrhizal nutrient uptake can occur.     

Categories of vesicular-arbuscular mycorrhizal dependency of host species

Summary Brassica nigra and selected species of Leucaena and Sesbania were used as indicator hosts in a greenhouse experiment designed to establish distinct categories of mycorrhizal dependence. The plants were grown in an oxisol with different concentrations of established soil solution P in the presence or absence of the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus aggregatum. The extent to which the plant species depended on the fungus for dry matter production diminished with increased concentrations of soil solution P, but the magnitude of this decrease varied from species to species. Five distinct mycorrhizal categories are proposed based on the differences observed, ranging from non-dependent to very highly dependent. The critical soil solution P concentrations that were useful for separating host species into distinct VAM-dependency groups were 0.02 and 0.2 mg/l. Species differing in their mycorrhizal dependency differed with respect to the soil solution P concentration required for the expression of maximum VAM effectiveness, the degree to which increasing concentrations of P depressed VAM infection and the pattern of immobile nutrient accumulation.Contribution from the Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No. 3547     

Effectiveness of VAM fungi in nonsterile soils before and after optimization of P in soil solution

Five tropical soils were either not inoculated or inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus aggregatum. The degree to which VAM effectiveness was expressed in the soils was evaluated prior and after solution P status was adjusted for optimal VAM activity. VAM effectiveness determined by monitoring P concentrations of pinnules of Leucaena leucocephala leaves as a function of time and as dry matter yield determined at the time of harvest, indicated that in three of the soils VAM effectiveness was either very restricted or altogether unexpressed irrespective of vesicular-arbuscular mycorrhizal fungal (VAMF) inoculation if soil solution P was not optimized for VAM effectiveness. After P optimization, effectiveness was significantly increased by VAMF inoculation although in four of the soils, densities of indigenous VAMF propagules greatly exceeded that attained by the inoculum after it was mixed with soil. Mycorrhizal fungal inoculation effects varied from soil to soil, depending on the extent to which the effectiveness of indigenous and introduced endophytes was enhanced by P optimization and the similarity of inherent soil solution P concentrations to the range known to be optimum for VAM effectiveness. Of the indicator variables monitored, VAMF colonization was least sensitive to treatment effects followed by shoot P concentration measured at the time of harvest.Contribution from Hawaii Institute of Tropical Agriculture and Human Resources Journal series No. 3781.Contribution from Hawaii Institute of Tropical Agriculture and Human Resources Journal series No. 3781.     

Effects of rhizosphere soil,vesicular-arbuscular mycorrhizal fungi and phosphate onPlantago major L. ssp.pleiosperma Pilger

Biotic factors in the rhizosphere and their effect on the growth ofPlantago major L. ssp.pleiosperma Pilger (Great plantain) were studied. In a pot experiment the effect on shoot growth of the addition of 2.5% rhizosphere soil at four levels of phosphate was highly dependent on the availability of phosphate: a promoting effect at low phosphate levels was observed while a reducing effect occurred at higher phosphate levels. As the roots were infected with vesicular-arbuscular mycorrhizal (VAM) fungi in the treatment with rhizosphere soil, two other experiments were set up to separate effects of the indigenous VAM fungi from effects of the total rhizosphere population. The uptake of phosphate and shoot growth was not decreased at higher phosphate availability when VAM inoculum was added alone or in combination with rhizosphere soil. The growth reducing effect of the rhizosphere soil could therefore not be ascribed only to mycorrhizal infection. The results suggest that biotic factors in the rhizosphere soil affect the phosphate uptake ofPlantago major ssp.pleiosperma. This may, under conditions of phosphate limitation, lead to an increase of phosphate stress and, subsequently, a growth reduction. Futhermore, it is concluded that VAM fungi, as part of the rhizosphere population, may compensate this phosphate stress by enhancing the phosphate uptake.Grassland Species Research Group Publication No. 148.     

A tripartite culture system for endomycorrhizal inoculation of micropropagated strawberry plantlets in vitro

The objective of the current investigation was to develop a reliable method to obtain vesicular arbuscular mycorrhizae (VAM) in micropropagated plantlets and to determine their influence on growth. An in vitro system for culturing the VA mycorrhizal fungus Glomus intraradices with Ri T-DNA-transformed carrot roots or nontransformed tomato roots was used in this study as a potential active source of inoculum for the colonization of micropropagated plantlets. After root induction, micropropagated plantlets grown on cellulose plugs (sorbarod) were placed in contact with the primary mycorrhizae in growth chambers enriched with 5000 ppm CO₂ and fed with a minimal medium. After 20 days of tripartite culture, all plantlets placed in contact with the primary symbiosis were colonized by the VAM fungus. As inoculum source, 30-day-old VA mycorrhizal transformed carrot roots had a substantially higher infection potential than 5-, 10-or 20-day-old VAM. Colonized plantlets had more extensive root systems and better shoot growth than control plants. The VAM symbiosis reduced the plantlet osmotic potential. This response may be a useful pre-adaptation for plantlets during transfer to the acclimatization stage.