Mycorrhizal Growth Response Research Articles

Suppression of vesicular–arbuscular mycorrhizal fungus spore germination by nonsterile soil

When the effect of nonsterile soil on vesicular–arbuscular mycorrhizal fungus spore germination was examined, significantly fewer Glomus etunicatum (22 vs. 63 and 64%) or Glomus mosseae (23 vs. 80 and 79%) spores germinated in nonsterile soil than in autoclaved or pasteurized soil, respectively. In some cases, addition of nonsterile soil sievings to autoclaved or pasteurized soil also reduced germination, as compared with germination in unamended pasteurized or autoclaved soil. Germination was reduced by as much as 45% in autoclaved or pasteurized soil if spores were surface sterilized. However, surface sterilization of G. etunicatum spores did not affect dry weight of inoculated big bluestem plants, but mycorrhizal root colonization was reduced when spore-associated microbes were removed from spores by surface sterilization. The detrimental effect of soil microbes on spore germination and mycorrhizal growth response may reflect microbial competition for nutrients since germination of G. etunicatum and G. mosseae was reduced when pasteurized soil was amended with 15, 30, or 60 ppm phosphorus and 60 ppm phosphorus, respectively. An optimum range of available phosphorus may exist, above or below which germination is suppressed.

Suppression of Mycorrhizal Growth Response of Big Bluestem by Non-Sterile Soil

Inoculum potential of Glomus mosseae and Glomus etunicatum was reduced significantly in pasteurized soil amended with a sieved suspension from non-sterile soil. Regardless of mycorrhizal fungus inoculum dosage, dry weight and root colonization of plants grown in pasteurized soil with non-sterile soil sievings never equalled those of plants grown in pasteurized soil alone. However, plants exposed to non-sterile soil were more colonized and grew faster than plants in pasteurized soil alone. Only after 13 wk were plants in pasteurized soil significantly more colonized, and after 16 wk larger in dry weight than their counterparts in non-sterile soil or pasteurized soil with sievings. Apparently, loss of inoculum potential alone cannot fully explain the suppression of plant growth observed in non-sterile soil. The suppressive effects of non-sterile soil may be best related to microbial mediation of nutrient availability in soil.

Suppression of Mycorrhizal Growth Response of Big Bluestem by Non-Sterile Soil

Suppression of Mycorrhizal Growth Response of Big Bluestem by Non-Sterile Soil

Mycorrhizal growth responses: interactions between photon irradiance and phosphorus nutrition

The effects of photon irradiance, phosphorus (P) supply and mycorrhizal infection [Glomus mosseae (Nicol. and Gerd) Gerdemann and Trappe] on growth and P uptake by Allium cepa L. were measured. Two experiments were carried out, one in a naturally-lit glasshouse and the other in a growth cabinet. Shade cloth was used to provide 'high' irradiance (600 and 550 μmol m-2 s-1 in glasshouse and growth cabinet respectively) and 'low' irradiance (250 μmol m-2 s-1 ). Growth at high irradiance was associated with increases in total dry weight, root: shoot dry weight ratio and total root length and with decreases in shoot fresh weight: dry weight ratio. Mycorrhizal growth responses were lower at low irradiance and depressions were observed at high P supply and high irradiance, as well as at low irradiance. Mycorrhizal plants generally had higher shoot fresh weight: dry weight ratios than those of equivalent non-mycorrhizal plants. Mycorrhizal infection was lower in the presence of additional P in both experiments. In the glasshouse there was an interaction between low irradiance and high P, leading to very low values of fractional infection. This effect was not apparent in the growth cabinet. At high irradiance mycorrhizal plants had higher inflows than those of equivalent non-mycorrhizal plants at all levels of P, regardless of the growth response. Low irradiance had little effect on inflow into non-mycorrhizal plants, but depressed inflow into mycorrhizal plants. This reduction in inflow can be attributed in part to lower levels of infection, but an effect on P uptake by hyphae or on transport between the symbionts is also likely.

A Spore Collection Apparatus for Vesicular-Arbuscular Mycorrhizal Fungi

Hetrick, B. A. Daniels, and J. Bloom. 1983. Vesicular-arbuscular mycorrhizal fungi associated with native tallgrass prairie and cultivated winter wheat. Canad. J. Bot. 61: 2140-2146. , J. A. Hetrick, and J. Bloom. 1984. Interaction of mycorrhizal infection, phosphorus level, and moisture stress in growth of field corn. Canad. J. Bot. 62: 2267-2271. agules from soil. Pp. 29-37. In: Methods and i ciples of mycorrhizal research. Ed , N. C. e ck. Am. Phytopathol. Soc., St. Paul, Min, D. Gerschefske Kitt, and G. Thompson Wilson. 1986. The influence of phosphorus fertilization, drought, fungal species and soil microorganisms on mycorrhizal growth response in tallgrass prairie plants. Canad. J. Bot. 64: 1199-1203. Ross, J. P. 1980. Effect of nontreated field soil on sporulation of vesicular-arbuscular mycorrhizal fungi associated with soybean. Phytopathology 70: 1200-1205. sc efske Ki t, and G. Thompson Wilson. . e influence of phosphorus fertilization, , fungal species and soil microorganisms rhizal growth response in tallgrass pra rie . a ad. J. Bot. 64: 1 9-1203.

Sporulation of Two Vesicular-Arbuscular Mycorrhizal Fungi in Nonsterile Soil

Spore numbers and species diversity of vesicular-arbuscular mycorrhizal (VAM) fungi from agricultural soils may be significantly lower than those observed in native soils (Hetrick and Bloom, 1983). In a survey of corn fields from four locations throughout a growing season, one soil (Scandia, Kansas) contained primarily Gigaspora spp. at all sample dates (G. rosea was present on two of the sample dates) while the others contained primarily or exclusively Glomus spp., including G. etunicatum (Hetrick et al., 1984). The present study was initiated to determine whether the Scandia soil favored sporulation of Gigaspora spp. and conversely whether a soil containing predominantly Glomus spp. would preferentially stimulate Glomus spp. sporulation. Because nonsterile soil has been shown to suppress mycorrhizal growth response and root colonization (Hetrick et al., 1986), the effect of nonsterile versus sterilized soil and interspecific competition on sporulation was also studied to determine whether these factors influenced species dominance and might also explain the low spore numbers observed in agricultural soils. A Chase, silty clay loam (fine montmorillonitic, mesic Aquic Argiudoll) from Manhattan, Kansas, previously cropped to corn for several years, and containing only Glomus spp. (primarily G. etunicatum) was chosen for comparison with Scandia soil which is a Crete silt loam (fine montmorillonitic, mesic Typic Argiustoll) containing primarily Gigaspora spp. (including but not limited to G. rosea). Each soil was shredded to eliminate large clods and homogenized in

Growth of Three Native Prairie Perennials as Influenced by Phosphorus Fertilization, Potting Media, and Mycorrhizae

Abstract Seedlings of blue wildindigo [Baptisia australis (L.) R. Br.], rough gayfeather (Liatris aspera Michx.), and butterfly milkweed (Asclepias tuberosa L.) were grown in either a 1 soil : 1 sphagnum peat : 1 perlite (by volume) or 1 soil : 1 sand medium (v/v), amended with 0.00, 0.29, or 0.58 kg P/m3, and inoculated with Glomus etunicatum Becker and Gerd., G. fasciculatum (Thax. sensu Gerd.) Gerd. and Trappe, G. macrocarpum Tul. and Tul., G. mosseae (Nicol. and Gerd.) Gerd. and Trappe, or remained noninoculated. The objective was to determine whether vesicular-arbuscular mycorrhizal (VAM) fungi can establish and enhance plant growth, and how this would be affected by soil amendments. Replications were transplanted into the field to determine whether VAM pretransplant inoculation increased host growth and flowering. In the greenhouse, total dry weight of the three wildflower species grown in 1 soil : 1 sand (v/v) medium with no P was significantly improved by addition of most mycorrhizal species tested, but the response varied among plant species. At 0.29 kg P/m3, fewer mycorrhizal growth responses were evident. No growth responses were evident at 0.58 kg P/m3. B. australis was the only species that benefited from mycorrhizal inoculation in the 1 soil: 1 sphagnum peat: 1 perlite (by volume) medium at 0.00 and 0.29 kg P/m3. There were no differences in tissue P content within the three species when VAM-inoculated plants at 0.00 kg P/m3 were compared to noninoculated controls. At 0.29 kg P/m3 in the 1 soil : 1 sand medium, inoculated seedling tissue P increased, but in the 1 soil : 1 sphagnum peat : 1 perlite medium, noninoculated controls had significantly higher tissue P contents compared to inoculated seedlings. In the field, height and inflorescences per plant for the wildflowers were improved by VAM inoculation during the 2nd growing season.

Evaluation of Ericoid Mycorrhizae and Media, on Establishment of Micropropagated, Rhododendron chapmanii, Gray

Rooted microcuttings of Chapman's rhododendron (Rhododendron chapmanii Gray) were transplanted into MetroMix-500 (M500) and fired montmorillonite clay: Canadian peat [(2FMC: 1CP) by vol] and half the plantlets were inoculated with the ericoid mycorrhizal fungus, Pezizella ericae Read. Plantlet survival was improved with mycorrhizal colonization after 16 weeks in 2FMC: 1CP medium, but no differences were observed for plants grown in the M500 medium. Plant growth parameters after 16 weeks were greater for all plants grown in the M500 medium and there were no beneficial mycorrhizal growth responses in either media. Mycorrhizal colonization appeared to be of no benefit to growth of rooted R. chapmanii microcuttings except improved survival in high pH 2FMC:1CP medium.

The influence of phosphorus fertilization, drought, fungal species, and nonsterile soil on mycorrhizal growth response in tall grass prairie plants

In a series of experiments, factors effecting mycorrhizal growth response in prairie plants were examined. Two prairie grasses (Andropogon gerardii Vitman and Sorghastrum nutans (L.) Nash) and two forb species (Petalostemum purpureum (Venten) Rydb. and Liatris punctata Hook) benefited significantly from Glomus etunicatum Becker & Gerd. inoculation in fumigated or steamed soil. This benefit from mycorrhizae is probably related to phorphorus availability, since addition of 100 ppm phosphorus overcame the mycorrhizal growth response. No stimulation of growth occurred from additional vesicular–arbuscular, mycorrhizal inoculum to nonsterile soil. Neither was growth in nonsterile soil comparable to that achieved in inoculated, sterilized soil, suggesting a suppression of mycorrhizal growth response in nonsterile soil. In a related experiment addition of 1 or 10% nonsterile soil to sterilized, inoculated soil resulted in significantly reduced plant growth and greatly diminished mycorrhizal root colonization. Thus, soil microorganisms may suppress mycorrhizal growth responses, explaining the lack of mycorrhizal growth response observed in nonsterile soil. Of the four mycorrhizal fungi compared (Gigaspora rosea Nicol. & Schenk, Glomus deserticolum Trappe, Bloss & Menge, Glomus etunicatum Becker & Gerd., and Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe), the two indigenous species most stimulated plant growth. Under severe moisture stress (−4500 kPa) a significant mycorrhizal growth response was evident for G. etunicatum, but not for G. deserticolum inoculated plants. Growth response does not necessarily suggest drought tolerance, since the magnitude of response was similar in adequately watered and severely draughted plants.

The interaction of vesicular-arbuscular mycorrhizae and soil phosphorus fertility on growth of sweet potato (Impomoea batatas)

Three sweet potato cultivars were inoculated with vesicular-arbuscular mycorrhizal (VAM) fungi and grown in different phosphorus fertility regimes to determine their effects on plant growth. Plants responded well to phosphorus fertilization and to a certain degree to VAM. In some tests VAM fungi were as effective in stimulating growth as an additional 800 μg P/g soil. In al studies the mycorrhizal growth response was greatest at low fertility, but in general all cultivars showed a low degree of mycorrhizal dependency. This is the first report of the influence of vesicular-arbuscular mycorrhizae on growth of sweet potato. The role of VAM fungi in enhancing growth and possible explanations for the observed results are discussed.

Effect of Container Plant Growth Medium and Fertilizer Phosphorus on Establishment and Host Growth Response to Vesicular–Arbuscular Mycorrhizae

Abstract The establishment and performance of vesicular–arbuscular mycorrhizae (VAM) formed by Glomus fasciculatum (Thaxter) Gerd. & Trappe were studied on geranium (Pelargonium × hortorum L.H. Bailey) and subterranean clover (Trifolium subterraneum L.) in various growth media at 2 P fertility levels. Colonization by G. fasciculatum was not extensive and shoot dry weight and P uptake consequently were not increased by VAM in soilless media such as peat, bark, perlite, and vermiculite. In media containing soil and fertilized at the low P level, roots were colonized extensively by G. fasciculatum, and host shoot growth and P concentrations were increased by VAM. Host growth enhancement by VAM was not observed at the higher P fertility level. Differences in colonization and mycorrhizal response in different fertilized growth media were correlated negatively with the logarithm of the equilibrium solution P concentration. Colonization, growth response, and P uptake by geranium inoculated with G. mosseae (Nic. & Gerd.) Gerd. & Trappe or Acaulospora spinosa Walker & Trappe were affected by growth medium and P fertilizer in the same way as plants inoculated with G. fasciculatum. Peat mosses from different sources varied considerably in their effects on mycorrhiza formation by G. fasciculatum, and on growth response of geranium when the peat was diluted with different amounts of soil. These differences appeared to be related to the equilibrium solution P concentration of the fertilized peats, and not to extractable P of the unfertilized peats. Use of rock phosphate or bonemeal instead of NaH2PO4 as a source of P did not improve the establishment of VAM and host growth response in soil, peat, or vermiculite. Addition of 5–10% Turface, bentonite, silt loam soil, or clay subsoil to peat or vermiculite resulted in increased colonization of host roots and significant mycorrhizal growth response, whereas amendment with liquid sludge inhibited formation of mycorrhizae.

ACTIVITY OF NITRATE REDUCTASE IN TRIFOLJUMSUBTERRANEUM: EFFECTS OF MYCORRHIZAL INFECTION AND PHOSPHATE NUTRITION

SummaryActivity of nitrate reductase (NADH‐dependent), measured by in vitro methods, was present in both roots and shoots of non‐mycorrhizal Trifolium subterraneum. As expected, the activity was dependent upon the amount of nitrate supplied and was closely related to the concentration of nitrate in the tissues.Mycorrhizal plants had a greater capacity to synthesize the enzyme in both roots and shoots than non‐mycorrhizal plants when both were grown under phosphate‐limiting conditions. This conclusion was reached from the results of two types of experiment: (1) when constant (relatively low) amounts of nitrate were supplied to the plants each day, the specific activity of the enzyme in the roots declined over the period of the experiment (52 days) as the plants grew larger. There was also a decline in shoots of mycorrhizal plants. However, when the nitrate supply was increased fourfold, the stimulation of activity was considerably greater in the roots of mycorrhizal plants than in non‐mycorrhizal plants; (2) interactions between mycorrhizal infection, phosphate nutrition and nitrate reductase activity were investigated in plants which received different amounts of nitrate according to size. At the two lowest levels of additional soil phosphate (0 and 0.2 mmol phosphate per kg), there was a large mycorrhizal growth response accompanied by reduction in root: shoot ratio, increase in the phosphate concentration in the tissues and considerable stimulation of nitrate reductase activity, both on fresh weight and whole plant bases. This stimulation (together with changes in root: shoot ratio and phosphate concentration) was also apparent at 0.4 mmol phosphate per kg in the absence of any overall mycorrhizal growth response. At 0.67 mmol phosphate per kg, there was neither a growth response nor any stimulation of enzyme activity.NADPH‐dependent nitrate reductase activity, more characteristic of fungi than NADH‐dependent activity, was barely detectable and similar (very low) activity was present in both mycorrhizal and non‐mycorrhizal roots. The conclusions are that mycorrhizal effects on nitrate reductase activity are largely indirect, mediated via improved phosphate nutrition and that direct involvement of the fungi in nitrate assimilation is likely to be very slight.

Phosphate response curves of mycorrhizal and non-mycorrhizal plants

Abstract Clover plants were grown with or without mycorrhizal fungi in two soils fertilised with superphosphate at rates ranging from 0 to 280 mg P/610 ml pot (equivalent to 0–248 kg P/ha). After 175 days' growth in Dunmore soil, mycorrhizal plants significantly outyielded non-mycorrhizal (control) plants at fertiliser levels up to 200 mg P/pot. Mycorrhizal growth responses were smaller in Waingaro soil, but after 91 days' growth, control and mycorrhizal plants achieved 80% of maximum shoot growth at 125 and 50 mg P/pot respectively. Recovery of phosphate fertiliser was low and ranged from 5 to 20% in Dunmore soil and from 6 to 25% in Waingaro soil.

Factors Affecting Vesicular-Arbuscular Mycorrhizal Development and Growth of Cotton

SUMMARYThe influence of inoculum level, soil fertility, soil temperature, and cotton cultivar on vesicular-arbuscular mycorrhizal development and plant growth were determined. In a phosphorus-deficient soil, inoculum levels of either 200 or 400 azygospores of Gigaspora margarita per plant significantly stimulated cotton growth, whereas rates of 10, 50, and 100 spores per plant had little or no effect. In a soil deficient in nitrogen and phosphorus, G. margarita increased plant growth only when sufficient nitrogen was added, but the mycorrhizal growth response was not as great as when both nitrogen and superphosphate were added to non-mycorrhizal plants. When phosphorus was deficient in the soil mix, mycorrhizal plants consistently had a higher content of this element in the foliage than did nonmycorrhizal cotton. Addition of superphosphate (25 μg or more of P/g of soil) to a soil containing 10 μg/g of phosphorus produced a growth increase at least equal to the growth response induced by G. margarita or Glomus etunicatus, and rates of 50 and 150 μg/g suppressed root infection. Maximum mycorrhizal development by G. margarita and subsequent cotton growth stimulation occurred at 30 and 24 C and was slight or absent at 19 or 14 C. Growth stimulation of five cotton cultivars inoculated with G. margarita varied considerably; Coker 310 and Stoneville 213 responded best, Acala 1517–70 and Deltapine 16 were marginally influenced, and Paymaster 909 was relatively unaffected.

Factors Affecting Vesicular-Arbuscular Mycorrhizal Development and Growth of Cotton

SUMMARYThe influence of inoculum level, soil fertility, soil temperature, and cotton cultivar on vesicular-arbuscular mycorrhizal development and plant growth were determined. In a phosphorus-deficient soil, inoculum levels of either 200 or 400 azygospores of Gigaspora margarita per plant significantly stimulated cotton growth, whereas rates of 10, 50, and 100 spores per plant had little or no effect. In a soil deficient in nitrogen and phosphorus, G. margarita increased plant growth only when sufficient nitrogen was added, but the mycorrhizal growth response was not as great as when both nitrogen and superphosphate were added to non-mycorrhizal plants. When phosphorus was deficient in the soil mix, mycorrhizal plants consistently had a higher content of this element in the foliage than did nonmycorrhizal cotton. Addition of superphosphate (25 μg or more of P/g of soil) to a soil containing 10 μg/g of phosphorus produced a growth increase at least equal to the growth response induced by G. margarita or Glomus etunicatus, and rates of 50 and 150 μg/g suppressed root infection. Maximum mycorrhizal development by G. margarita and subsequent cotton growth stimulation occurred at 30 and 24 C and was slight or absent at 19 or 14 C. Growth stimulation of five cotton cultivars inoculated with G. margarita varied considerably; Coker 310 and Stoneville 213 responded best, Acala 1517–70 and Deltapine 16 were marginally influenced, and Paymaster 909 was relatively unaffected.

Effect of inoculum rate on mycorrhizal growth responses in pot-grown onion and clover

White clover and onion plants were grown from seed in pots of sandy loam above pads of mycorrhizal inoculum soil at 0.17–1.40 g/pot (equivalent to 250–2000 kg/ha) and harvested on four occasions. In sterilized soil increasing inoculum rates increased the onset and size of the mycorrhizal growth response of white clover. In unsterilized soil the indigenous mycorrhizal fungi greatly stimulated growth of both clover and onion. Nevertheless, all mycorrhizal inoculum rates further stimulated shoot growth in onion (92% increase over all harvests), while only the highest inoculum rate significantly stimulated clover growth (52% increase).

Phosphate response curves of mycorrhizal and non-mycorrhizal plants

Clover plants were grown with or without mycorrhizal fungi in two soils fertilised with superphosphate at rates ranging from 0 to 280 mg P/610 ml pot (equivalent to 0–248 kg P/ha). After 175 days' growth in Dunmore soil, mycorrhizal plants significantly outyielded non-mycorrhizal (control) plants at fertiliser levels up to 200 mg P/pot. Mycorrhizal growth responses were smaller in Waingaro soil, but after 91 days' growth, control and mycorrhizal plants achieved 80% of maximum shoot growth at 125 and 50 mg P/pot respectively. Recovery of phosphate fertiliser was low and ranged from 5 to 20% in Dunmore soil and from 6 to 25% in Waingaro soil.

Growth of white clover in undisturbed soils after inoculation with efficient mycorrhizal fungi

Abstract Clover seedlings were inoculated with the indigenous or one of three introduced mycorrhizal fungi and transplanted into undisturbed cores of eight hill country soils. After several harvests, at least one of the introduced fungi had increased shoot growth in each soil from between 16 to 117%. In most soils, the growth benefit from inoculating with an introduced mycorrhizal fungus tended to decrease after the initial shoot harvest, and was then maintained at a lower level over subsequent harvests. In a Taihape silt loam, however, the growth benefit from Glomus tenuis inoculation increased steadily over six harvests. In four out of five soils, previous application of phosphate fertiliser (50 kg P/ha/year) did not reduce mycorrhizal growth responses.

EFFECT OF ARBUSCULAR MYCORRHIZA ON PLANT GROWTH

SUMMARYDefoliation of maize and tomatoes reduced the mycorrhizal growth response and development of the endophyte, estimated as percentage infection, root pigmentation and spore production. More fresh and dry matter was produced in mycorrhizal grasses harvested on three separate occasions than from a single final harvest. The total yields from two harvests and the yield from a single harvest of alfalfa were similar although nodulated and mycorrhizal plants were larger at each harvest. In both grasses and alfalfa, periodic harvesting reduced the mycorrhizal infection by approximately 50%.Reduction in daylength and irradiance depressed the growth more in mycorrhizal than in uninfected maize plants. In Rhizobium‐ and Glomus‐infected alfalfa plants, a daylength of 16 h produced the highest carbon contents and C/N ratios. Plants exposed to short days produced more, smaller nodules and had higher nitrogen contents than plants given long days. Long days favoured the development of the mycorrhizal infection and these dually infected plants produced more dry matter, reduced acetylene faster and contained more nitrogen than nodulated only plants. The supply of photosynthate is probably an important factor controlling the development of the mycorrhiza.

Enzymatic studies on the metabolism of vesicular-arbuscular mycorrhiza II. Soluble alkaline phosphatase specific to mycorrhizal infection in onion roots

Soluble alkaline phosphatase specific to vesicular-arbuscular mycorrhizal infection has been demonstrated in enzyme extracts from onion roots inoculated with Glomus mosseae. A close correlation existed between the mycorrhiza-specific phosphatase activity and development of both the infection and the host plant. Maximum activity occurred whilst the infection was still young (100% arbuscular) and coincided with the start of the mycorrhizal growth response, declining afterwards as plant development and infection continued. Enzyme activity was optimal in the presence of 10 −5 m orthomosphate but was markedly depressed at concentrations above 10 −4 m. The properties of mycorrhiza-specific alkaline phosphatase were characteristic of alkaline phosphomonesterase (EC 3.1.3.1.): optimal activity at alkaline pH; inhibition by metal chelating agents, certain cations and orthophosphate; requirement for Mg 2+ and Mn 2+ ions; hydrolysis of β-glycerol, phenyl and naphthyl phosphates; inability to hydrolyse more complex phosphate esters. The possible implications of these results with respect to mechanisms involved in the assimilation of phosphorus in the VA mycorrhizal system and/or the establishment of VA mycorrhizal infection are discussed.