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.     

Effect of salinity on mycorrhizal onion and tomato in soil with and without additional phosphate

Summary Vesicular-arbuscular mycorrhizal fungi (VAM) are known to increase plant growth in saline soils. Previous studies, however, have not distinguished whether this growth response is due to enhanced P uptake or a direct mechanism of increased plant salt tolerance by VAM. In a glasshouse experiment onions (Allium cepa L.) were grown in sterilized, low-P sandy loam soil amended with 0, 0.8, 1.6 mmol P kg^–1 soil with and without mycorrhizal inoculum. Pots were irrigated with saline waters having conductivities of 1.0, 2.8, 4.3, and 5.9 dS m^–1. Onion colonized withGlomus deserticola (Trappe, Bloss, and Menge) increased growth from 394% to 100% over non-inoculated control plants when soil P was low ( 0.2 mmol kg^–1 NaHCO₃-extractable P) at soil saturation extract salinities from 1.1 dS m^–1 to 8.8 dS m^–1. When 0.8 and 1.6 mM P was added no dry weight differences due to VAM were observed, however, K and P concentrations were higher in VAM plants in saline treatments.Glomus fasciculatum (Gerdeman and Trappe) andGlomus mosseae (Nicol. and Gerd.) isolates increased growth of VAM tomato 44% to 193% in non-sterilized, saline soil (10 dS m^–1 saturation extract) despite having little effect on growth in less saline conditions when soil P was low. Higher tomato water potentials, along with improved K nutrition by VAM in onion, indicate mechanisms other than increased P nutrition may be important for VAM plants growing under saline stress. These effects appear to be secondary to the effects of VAM on P uptake.     

A fungal root symbiont modifies plant resistance to an insect herbivore

Vesicular-arbuscular mycorrhizal (VAM) fungi are common root-colonizing symbionts that affect nutrient uptake by plants and can alter plant susceptibility to herbivores. I conducted a factorial experiment to test the hypotheses that colonization by VAM fungi (1) improves soybean (Glycine max) tolerance to grazing by folivorous Mexican bean beetle (Epilachna varivestis), and (2) indirectly affects herbivores by increasing host resistance. Soybean seedlings were inoculated with the VAM fungus Glomus etunicatum or VAM-free filtrate and fertilized with high-[P] or low-[P] fertilizer. After plants had grown for 7 weeks first-instar beetle larvae were placed on bagged leaves. Growth of soybean was little affected by grazing larvae, and no effects of treatments on tolerance of soybeans to herbivores were evident. Colonization by VAM fungus doubled the size of phosphorus-stressed plants but these plants were still half the size of plants given adequate phosphorus. High-[P] fertilizer increased levels of phosphorus and soluble carbohydrates, and decreased levels of soluble proteins in leaves of grazed plants. Colonization of grazed plants by VAM fungus had no significant effect on plant soluble carbohydrates, but increased concentration of phosphorus and decreased levels of proteins in phosphorus-stressed plants to concentrations similar to those of plants given adequate phosphorus. Mexican bean beetle mass at pupation, pupation rate, and survival to eclosion were greatest for beetles reared on phosphorus-stressed, VAM-colonized plants, refuting the hypothesis that VAM colonization improves host plant resistance. VAM colonization indirectly affected performance of Mexician bean beetle larvae by improving growth and nutrition of the host plant. Received: 28 February 1997 / Accepted: 23 June 1997     

Interaction of vascular plants and vesicular-arbuscular mycorrhizal fungi across a soil moisture-nutrient gradient

Summary Abundance and distribution of vascular plants and vesicular-arbuscular mycorrhizal (VAM) fungi across a soil moisture-nutrient gradient were studied at a single site. Vegetation on the site varied from a dry mesic paririe dominated by little bluestem (Schizachyrium scoparium) to emergent aquatic vegetation dominated by cattail (Typha latifolia) and water smartweed (Polygonum hydropiperoides). Plant cover, VAM spore abundance, plant species richness, and number of VAM fungi represented as spores, had significant positive correlations with each other and with percent organic matter. The plant and VAM spore variables had significant negative correlations with soil pH and available Ca, Mg, P and gravimetric soil moisture. Using stepwise multiple regression, Ca was found to be the best predictor of spore abundance. Test for association between plant species and VAM fungal spores indicated that the spores of Glomus caledonium are associated with plants from dry, nutrient poor sites and spores of gigaspora gigantea are positively associated with plants occurring on the wet, relatively nutrient rich sites. Glomus fasciculatum was the most abundant and widely distributed VAM fungus and it had more positive associations with endophyte hosts than the other VAM fungi. We found no relationship between beta niche breadth of plant species and the presence or absence of mycorrhizal infection. However, our data suggest that some plant species may vary with respect to their infection status depending upon soil moisture conditions that may fluctuate seasonally or annually to favor or hinder VAM associations.     

SEASONAL NUTRIENT DYNAMICS,NUTRIENT RESORPTION,AND MYCORRHIZAL INFECTION INTENSITY OF TWO PERENNIAL FOREST HERBS

Patterns of mycorrhizal infection, seasonal foliar nutrient concentrations, nutrient allocation to shoots and rhizomes, and nutrient resorption were measured in relation to soil nutrient availability in two species of perennial forest herbs, Geranium maculatum L. and Polygonatum pubescens Pursh., in four forest stands in southern and central Ohio. The percentage of plants with V-A mycorrhizae and the proportion of root length colonized by VAM structures increased with decreasing nutrient availability in both species. Foliar N and P concentrations in plants from lower fertility sites were as high, or higher, than those in plants from higher fertility sites; as a result, tissue nutrient enrichment ratios (foliar concentration/soil available concentration) increased with decreasing fertility. Proportional resorption of N and P generally decreased with decreasing nutrient availability, a pattern inconsistent with those exhibited by woody plants in these forest stands. We hypothesize that the inverse relationship between nutrient uptake efficiency (via mycorrhizae) and nutrient use efficiency (resorption) exhibited by these forest understory herbs, but not by trees or herbs from high-light environments, may be related to low-light limitation of energy reserves in the forest understory.     

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.     

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.     

Parasitic and mutualistic associations between a mycorrhizal fungus and soybean: The effect of phosphorus on host plant-endophyte interactions

Soybean [ Glycine max (L.) Merr. cv. Kent] plants were colonized by the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus fasciculatum (Thaxt. sensu Gerd.) Gerd. and Trappe in pot cultures using an inert medium and a nutrient solution. Phosphorus was provided initially as 0, 25,50, 100 or 200 mg hydroxyapatite [HAP, Ca₁₀(PO₄)₆(OH)₂] per pot. Under the low (0 mg HAP) and high (100 and 200 mg HAP) P regimes, VAM plants showed 20, 25 and 38% growth retardation, respectively, relative to non-colonized controls. At 50 mg HAP, VAM plant growth was significantly enhanced (14%). Dry weight and P content of both VAM and control plants increased with increased P availability throughout the HAP gradient. Intraradical VAM fungal biomass increased linearly with increasing P availability. Extraradical VAM fungal biomass was smaller than the intraradical component of the fungus at the lowest and highest levels of P addition in the growth medium. The ratio of extra- to intraradical mycelium, a suggested index of VAM fungal effectiveness, was greatest for the 50 mg HAP treatment, coinciding with growth enhancement of the host plant. This enhanced growth of the host at an intermediate P level was apparently a result of increased P uptake by the endophyte.     

Receptivity of various wheat cultivars to infection by VA-mycorrhizal fungi as influenced by inoculum potential and the relation of VAM-effectiveness to succinic dehydrogenase activity of the mycelium in the roots

Wheat cultivars grown in pots in a greenhouse were inoculated either once or twice with the vesicular-arbuscular mycorrhizal fungus (VAMF) Glomus mosseae. If inoculum was only added to the soil once (before planting) the cultivars showed differences in subsequent VAM development. If additional inoculum was added ten days after planting, VAM development was much increased and cultivars which remained without VAM after only one inoculum application now became mycorrhizal.Succinate dehydrogenase (SDH) activity decreased throughout the experiment, but this decrease was less rapid in mycelium in twice-inoculated plants.No close relationship between SDH-activity and plant growth (VAM effectiveness) was found.     

Effects of VA mycorrhiza on the growth of cacao seedlings under nursery conditions in Venezuela

The effects of vesicular-arbuscular mycorrhizae inoculation on the growth of cacao seedlings (Theobroma cacao var. Ocumare 60) grown for 5 months in a nursery were studied. The effects of introduced VAM fungi (Glomus occultum, Acaulospora appendicula, Glomus manihotis, Acaulospora morrowae and Scutellospora pellucida) in soils treated with copper oxychloride or methyl bromide, were compared with the indigenous VAM and with their respective non-inoculated controls.Cacao seedlings responded well to indigenous VAM fungi, which included Scutellospora calospora as the dominant species, inducing increases significant in height, dry weight and foliar uptake of P, Cu and Zn in relation to the sterile control. G. occultum and A. appendicula increased the height of cacao seedlings but to an extent not yet statistically significant through the duration of the experiment. S. pellucida and A. appendicula doubled the phosphorus uptake of cacao seedlings. The methyl bromide sterilization induced the lowest Cu and Zn uptake in the cacao seedlings but this effect was ameliorated with VAM inoculation. Manifest deficiency symptoms were not observed in the treatments.Copper oxychloride treatment depressed growth to the same level as the sterile control although its residual effects did not kill VAM. It could change the competitive relations among the VAM species and in this case seemed to affect adversely the more efficient native fungi.The influence of the presence and long permanence of large cotyledons in cacao on the results obtained is discussed.     

Effects of belowground grazing by collembola on growth,mycorrhizal infection,and P uptake of Geranium robertianum

We hypothesized that the grazing of vesicular-arbuscular mycorrhizal (VAM) hyphae by soil animals could be responsible for the lack of a direct relationship between mycorrhizal infection intensity and nutrient uptake under field conditions. To test this hypothesis, we determined the effect of a range of densities of the collembola, Folsomia candida, on growth, VAM infection, and P uptake in Geranium robertianum, a common forest herb, under greenhouse conditions. Total and aboveground growth were greater at low collembola density than either at higher collembola density or without collembola. These differences were greater when the plants were grown in a high organic content soil mix than when grown in sand. Root mass was not affected by collembola density. In the soil mix, root length decreased with increasing collembola density, but not in the sand. The percent of root length infected with VAM was lower at any collembola density than when collembola were absent. Total infected root length decreased linearly with increasing collembola density. Few significant differences in P uptake or tissue concentration were found. Thus, plant growth (but not P uptake) may be stimulated at low collembola density and inhibited at high. We discuss mechanisms which may be responsible for this non-linear response, and the implications of the pattern of response to studies of plant competition, nutrient turnover, and revegetation.     

Response of citronella Java (Cymbopogon winterianus Jowitt) to VA mycorrhizal fungi and soil compaction in relation to P supply

Nutrient acquisition and growth of citronella Java (Cymbopogon winterianus Jowitt) was studied in a P-deficient sandy soil to determine the effects of mycorrhizal symbiosis and soil compaction. A pasteurized sandy loam soil was inoculated either with rhizosphere microorganisms excluding VAM fungi (non-mycorrhizal) or with the VAM fungus, Glomus intraradices Schenck and Smith (mycorrhizal) and supplied with 0, 50 or 100 mg P kg^-1 soil. The soil was compacted to a bulk density of 1.2 and 1.4 Mg m^-3 (dry soil basis). G. intraradices substantially increased root and shoot biomass, root length, nutrient (P, Zn and Cu) uptake per unit root length and nutrient concentrations in the plant, compared to inoculation with rhizosphere microorganisms when the soil was at the low bulk density and not amended with P. Little or no plant response to the VAM fungus was observed when the soil was supplied with 50 or 100 mg P kg^-1 soil and/or compacted to the highest bulk density. At higher soil compaction and P supply the VAM fungus significantly reduced root length. Non-mycorrhizal plants at higher soil compaction produced relatively thinner roots and had higher concentrations and uptake of P, Zn and Cu than at lower soil compaction, particularly under conditions of P deficiency. The quality of citronella Java oil measured in terms citronellal and d-citronellol concentration did not vary appreciably due to various soil treatments.     

Response of lentil to VA Mycorrhizal inoculation and plant available P levels of unsterile soils

Summary Responses of lentil in unsterile soils at low, medium and high levels of plant available soil P toGlomus fasciculatum inoculation were evaluated. It was observed that growth, dry matter accumulation, nodulation, and nitrogen fixation were considerably improved in VAM inoculated plants over uninoculated control at low and medium levels of plant available soil P.     

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.     

Nutrient availability effects on vesicular-arbuscular mycorrhizal bell pepper (Capsicum annuum) seedlings and transplants

Pepper (Capsicum annuum) seeds were sown in nutrient-poor sand or nutrient-rich peat/vermiculite amended or not amended with Glomus macrocarpum. The vesicular-arbuscular mycorrhizal (VAM) seedlings were irrigated with three levels of nutrient solution, and transplanted into four levels of P-amended soil, each of which was irrigated with two levels of nutrient solution minus P. Mycorrhizal seedlings in sand were responsive to increasing nutrient levels; in nutrient-rich peat the seedlings did not respond to additional fertilisation. The greatest seedling development accompanied by good fungus colonisation was in nutrient-poor medium irrigated with the highest nutrient solution tested (18 mM N, 1.2 mM P, and 7 mM K). Non-VAM plants almost ceased growing between the weeks 4 and 5, whereas VAM plants increased in weight by 41–188%. After transplanting, sand-grown seedlings benefited from VAM when 300 mg P/kg or more was added to the soil but peat-grown plants did not. Fruit development was delayed in all non-VAM plants compared with VAM ones.     

Growth and nutrient status of citrus plants as influenced by mycorrhiza and phosphorus application

To test the hypothesis that high levels of soluble phosphate applied in combination with VAM fungi, to citrus plants, can cause growth depression even in the absence of other limiting factors, and also to test if rock phosphate, under these conditions, may be a satisfactory P source, a greenhouse experiment was conducted using sterilized soil with four levels of phosphate (0, 50, 100 and 200 ppm P) supplied either as soluble P or as rock phosphate. Citrus seedlings were either inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus etunicatum or left uninoculated. Six months after the start of the experiment, the plants were harvested and shoot dry weight, P and K uptake, root colonization and the number of spores in 50 cm³ of soil were determined. Significant increases were found in dry matter yields and in P and K contents, due to VAM fungus inoculation, at the zero and 50 ppm soluble P levels and at all rock phosphate levels. At 100 ppm soluble P, the development of VAM plants was equilvalent to that of non-VAM plants, and at 200 ppm, growth was significantly less than that of non-VAM plants. Root colonization and sporulation were reduced at higher P levels. The absolute growth depression of VAM plants at the higher P level was likely due to P toxicity. In addition, high leaf P and K concentrations may have interfered with carbohydrate distribution and utilization in these symbioses. Rock phosphate may be used with VAM citrus to substitute for medium amounts of soluble phosphate.     

Effect of vesicular-arbuscular mycorrhizal and phosphatase-producing fungal inoculation on growth and nutrition of white clover supplied with organic phosphorus

In a pot experiment white clover was grown for 50 d in two sterilized low phosphorus soils supplied with organic phosphorus as sodium phytate. Seed inoculation withAspergillus fumigatus, a phosphatase-producing fungus (PPF), and soil inoculation withGlomus mossece, a vesicular-arbuscular mycorrhizal (VAM) fungus resulted in increased shoot and root dry mass and root length, phosphatase activity in soil and shoot concentrations of P and to a lesser extent of Mg. The effects on these parameters were most distinct upon combined inoculation treatment (PPF+VAM). A significant increase in hyphal length density and decrease in Mn concentration was observed only upon PPF+VAM treatment. Shoot concentrations of Cu and Zn were highly enhanced by VAM but not by PPF. Of the total P uptake the PPF contribution accounted for 39–41 %, VAM contributed 41–50 % and their combination resulted in 55–58 %, in comparison to only 38–40 % contribution due to soil microorganisms under unsterilized conditions. The depletion of organic phosphorus in the rhizosphere soil increased in the order (PPF+VAM)>VAM>PPF> unsterilized soil>sterilized soil. The results demonstrate the efficient use of phytate phosphorus byA. fumigatus andG. mosseœ and suggest that dual inoculation is superior to a single one.     

Salinity and flooding stress effects on mycorrhizal and non-mycorrhizal citrus rootstock seedlings

Seedlings of the rootstocks Pineapple sweet orange (SwO), Carrizo citrange (CC), and sour orange (SO) were grown in low phosphorus (P) sandy soil and either inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus,Glomus intraradices, or were non-mycorrhizal (NM) and fertilized with P. VAM and NM seedings of similar shoot size and adequate P-status were selected for study of salinity and flooding stress. One-third of each of the VAM and NM plants were given 150 mM NaCl for a period of 24 days. One-third of the plants were placed into plastic bags and flooded for 21 days while the remaining third were non-stressed controls. In general, neither stress treatment affected mycorrhizal colonization. Salinity stress reduced the hydraulic conductivity of roots, leaf water potential, stomatal conductance and net assimilation of CO₂ (ACO₂) of mycorrhizal and non-mycorrhizal seedlings to a similar extent. VAM plants of CC and SO accumulated more Cl in leaves than NM plants. Cl was higher in non-mycorrhizal roots of SwO and CC than in mycorrhizal roots. Flooding the root zone for 3 weeks did not produce visible symptoms in the shoot but did influence plant water relations and reduce ACO₂ of all 3 rootstocks. VAM and NM plants of each rootstock were affected similarly by flooding. Comparable reduction in nitrogen and P content of both mycorrhizal and non-mycorrhizal plants suggested that flooding stress was primarily affecting root rather than hyphal nutrient uptake. Florida Agricultural Experimental Station Journal Series No. 7773.     

Effects of drought on host and endophyte development in mycorrhizal soybeans in relation to water use and phosphate uptake

Bethlenfalvay, G. J., Brown, M. S., Ames, R. N. and Thomas, R. S. 1988. Effects of drought on host and endophyte development in mycorrhizal soybeans in relation to water use and phosphate uptake. - Physiol. Plant. 72: 565–571.
Soybean [ Glycine max (L.) Merr.] plants were grown in pot cultures and inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe or provided with P fertilizer (non-VAM plants). After an initial growth period (21 days), plants were exposed to cycles of severe, moderate or no drought stress over a subsequent 28-day period by rewatering at soil water potentials of -1.0, -0.3 or -0.05 MPa. Dry weights of VAM plants were greater at severe stress and smaller at no stress than those of non-VAM plants. Phosphorus fertilization was applied to produce VAM and non-VAM plants of the same size at moderate stress. Root and leaf P concentrations were higher in non-VAM plants at all stress levels. All plants were stressed to permanent wilting prior to harvest. VAM plants had lower soil moisture content at harvest than non-VAM plants. Colonization of roots by G. mosseae did not vary with stress, but the biomass and length of the extraradical mycelium was greater in severely stressed than in non-stressed plants. Growth enhancement of VAM plants relative to P-fertilized non-VAM plants under severe stress was attributed to increased uptake of water as well as to more efficient P uptake. The ability of VAM plants to deplete soil water to a greater extent than non-VAM plants suggests lower permanent wilting potentials for the former.     

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.