Vesicular-arbuscular Mycorrhizae Colonization Research Articles

Performance of vesicular-arbuscular mycorrhizae in saline-alkali soil in relation to various amendments

The present study shows that vesicular-arbuscular mycorrhizal colonization in plants grown in saline-alkali soil is host dependent and it is significantly affected by various amendments given to reclaim such soils. Maximum reduction in vesicular-arbuscular mycorrhizal colonization was observed in the plants raised in saline-alkali soil amended with gypsum and maximum colonization was observed after plant-growth promoting rhizobacterium or farm yard manure amendments. Plants possessing high level of vesicular-arbuscular mycorrhizal colonization (50–70%) included Acacia nilotica, Albizia lebbeck and Dalbergia sissoo. Casuarina equisetifolia possessed moderate level of vesicular-arbuscular mycorrhizae colonization (30–50%) and Azadirachta indica possessed low level of colonization (20–40%).

Influence of Formononetin and NaCl on Mycorrhizal Colonization and Fusarium Crown and Root Rot of Asparagus.

Replanted asparagus fields commonly fail to produce a profitable stand due to alleopathic residues left behind from the previous asparagus crop, elevated densities of pathogenic Fusarium spp., and low densities of vesicular arbuscular mycorrhizae (VAM). Formononetin, a plant isoflavone that stimulates VAM spores to germinate, and sodium chloride (NaCl), a disease-suppressing amendment, were evaluated alone and in combination for their effect on reestablishing asparagus at two locations in abandoned asparagus fields. Greenhouse studies also were conducted with naturally and artificially infested soils. Formononetin was applied as a crown soak or soil drench, and NaCl was applied as a granular treatment. Feeder roots from soil cores sampled from field plots and from greenhouse transplants were assayed for colonization by VAM and for lesions caused by Fusarium oxysporum and F. proliferatum. Formononetin increased the number of VAM vesicles in roots from the field and greenhouse studies and reduced the percent root lesions caused by Fusarium spp. when compared with the nontreated controls. NaCl was more effective than formononetin in reducing the percentage of root lesions in both field and greenhouse experiment when compared with untreated plants but had no effect on VAM colonization. However, there was evidence that NaCl negated the effect of formononentin on VAM colonization. The NaCl treatment increased the May 2001 spear number by 15% and marketable spear weight by 23%. At one site, treatment with formononetin increased mean number of stalks per plant by 29% in 2000 and 14% in 2001. Both formononetin and NaCl improve growth and reduce disease of asparagus in replanted asparagus and may be useful in reestablishing asparagus in abandoned asparagus field.

INFLUENCE OF VESICULAR-ARBUSCULAR MYCORRHIZAE ON CELERY TRANSPLANT GROWTH AND PHOSPHORUS-USE EFFICIENCY

ABSTRACT Elevated phosphorus (P) levels present in Everglades Agricultural Area (EAA) stormwater runoff are an environmental concern for adjoining wetlands in South Florida. A regulatory program requires EAA growers to adopt best management practices that reduce P in farm drainage water. Given the prevailing regulatory climate, P fertilization practices are under scrutiny, and a premium is placed on identifying management practices that improve crop P-use efficiency. By enhancing root P uptake, vesicular-arbuscular mycorrhizae (VAM) can potentially reduce P inputs to celery (Apium graveolens L.) without compromising crop yields. The initial objective of this study was to determine whether celery infection by Glomus intraradices was feasible. Subsequent objectives included the assessment of plant growth response to VAM inoculation during the transplant production-dates printpubdate="07/01/2002" phase and quantification of VAM effects on P-use efficiency in celery. Pre-germinated celery seeds were direct-seeded into flats containing VAM-amended potting mix at concentrations of 0, 200, 500, and 1000 chlamydospores (30-mL mix)−1, for treatments V-0, V-200, V-500, and V-1000, respectively. Following 90 days growth, root colonization under low VAM amendments (V-200) ranged from 87.1% (Experiment #1) to 92.7% (Experiment #2), far exceeding the non-inoculated control (V-0; 0 to 3.7%). Relative to V-0, celery plants infected with VAM averaged 21.7 to 57.0% greater shoot dry matter, were 22.9 to 42.7% taller, supported 9.5 to 15.5% more petioles, and shoots had 8.6 to 23.0% greater P concentrations. Overall P-use efficiency, represented by top-growth P uptake, was 33.0 to 94.2% greater than the control. Under high VAM (V-1000) amendments, P uptake exceeded V-0 by 61.7 to 102.5%. Time-trend analyses indicate that shoot dry matter accumulation and P uptake trends over the 90-day growing period generally ranked as follows: V-1000>(V-500=V-200)>V-0. These results document successful VAM colonization in celery. Additionally, VAM confers improved growth performance and P-use efficiencies during celery transplant growth.

Selenium uptake by plants: Effects of soil steaming, root addition, and selenium augmentation

A greenhouse study was conducted to evaluate the effects of soil steaming, root additions, and selenium (Se) supplements on the uptake of Se by two plant species, yellow sweet clover [Melilotus officinalis (L.) Pallas], and fourwing saltbush [Atriplex canescens (Pursh) Nutt.]. Although treatments used to test the effects of vesicular‐arbuscular mycorrhizae (VAM) did not result in differences in Se uptake, both species of plants had significantly lower Se concentrations when grown in steamed soil (65–80°C, 14h). Whereas soil steaming did not affect the growth of yellow sweet clover, growth of fourwing saltbush was significantly enhanced. Root additions, added as mycorrhizal inoculum, had no effect on the growth parameters or Se uptake of the plants, but did enhanced VAM colonization of yellow sweet clover. Selenium (3 mg Se kg‐1) added as selenite (SeO3 2‐) increased plant Se concentrations, although selenate (SeO4 2‐) was fatal to most seedlings. Phosphate‐extractable soil Se concentrations were similar for SeO3 2‐ and SeO4 2‐amended treatments and were unaffected by root amendments or soil steaming treatments.

Vesicular-Arbuscular Mycorrhizae Influence Mount St. Helens Pioneer Species in Greenhouse Experiments

Vesicular-arbuscular mycorrhizae (VAM) are present in most terrestrial ecosystems and play a major role in community structure and function. However, their role in primary succession remains poorly understood. Two greenhouse studies examined the role of VAM in Mount St. Helens pioneer species under three nutrient regimes and four competitive scenarios. Nutrient levels were complete, complete without phosphorus (- P), and tap water (very low nutrient levels). In tap water a negative effect from VAM colonization was observed perhaps due to parasitic action of the VAM fungi. A weak but apparent benefit from VAM occurred in the -P treatment since plants in the -P treatment were usually not less in biomass than those in the complete nutrient treatment and VAM colonization levels were greater in the -P treatment. VAM colonization was more beneficial to plants under the complete nutrient treatment than under the tap water treatment. VAM assisted the facultatively mycotrophic Hypochaeris radicata in competition with the non-mycotrophic Carex mertensii. Lack of VAM improved the competitive ability of Carex mertensii when in competition with facultatively mycotrophic species. However, VAM did not significantly influence competitive outcomes between facultatively mycotrophic species.

Survey of vesicular–arbuscular mycorrhizae in lettuce production in relation to management and soil factors

The occurrence of vesicular–arbuscular mycorrhizae (VAM) root colonization and spore number in soil was assessed for 18 fields under intensive lettuce (Lactuca sativa L.) production in California during July and August of 1995. Data on management practices and soil characteristics were compiled for each field, and included a wide range of conditions. The relationship between these factors and the occurrence of VAM in these fields was explored with multivariate statistical analysis. VAM colonization of lettuce tended to decrease with the use of chemical inputs, such as pesticides and high amounts of P and N fertilizers. Addition of soil organic matter amendments, the occurrence of other host crops in the rotation, and soil carbon[ratio ]phosphorus and carbon[ratio ]nitrogen ratios, were positively associated with VAM colonization of lettuce roots. The number of VAM spores in soil was strongly correlated with the number of other host crops in the rotation, the occurrence of weed hosts and sampling date, but was more affected by general soil conditions than by management inputs. Higher total soil N, C and P, as well as CEC, were inversely related to soil spore number. A glasshouse study of the two primary lettuce types sampled in the field showed no significant differences in the extent of root colonization under similar growing conditions. The results of this study are compared with other studies on the effects of management and soil conditions on mycorrhizal occurrence in agriculture.

The Effect of Four Composts on the Establishment of Vesicular–Arbuscular Mycorrhizae in Soilless Media

The beneficial use of vesicular–arbuscular mycorrhizae (VAM) in mineral soils is well-documented, but little is known about the effect of soilless mixes on mycorrhizal colonization of roots. Previous research indicates that mycorrhizal colonization is affected by pH, soluble salts, phosphorus levels, cation exchange capacity, percent organic matter, and some peats. No other research has been published, to our knowledge, on the role of commonly used horticultural composts and mycorrhizal establishment. This study examined four different composts for their effect on VAM establishment using onion roots as an indicator. The composts used in the study were vermicompost, spent mushroom compost, yard waste compost, and processed manure fiber. Plant growth parameters, phosphorus (P) levels and rate of desorption, and microbial populations were analyzed in relation to the percent of VAM colonization of the roots. Significant differences were found in percent VAM colonization between composts. The primary factors influencing VAM colonization were the initial levels of P in the blends and the rate and amount of P released. The experiment raised questions about the balance between mineralized P and organic P in composts and their effect on VAM fungal spore germination.

Fallow- and Flooded-Soil Syndromes: Effects on Crop Production

Fallow Soil Syndrome has been a problem for farmers in arid areas, The first observations were made in the 1940s when crops failed to produce as expected when planted to fallowed fields. Recent flooding in the midwestern U.S. states caused extensive crop damage and left many areas barren of plant growth. There was concern that crop production problems would develop when subsequent crops were planted to previously flooded areas. Like Fallow Soil Syndrome, the symptoms of Flooded Soil Syndrome are P deficiencies developing in crops even when adequate soil P concentrations are measured. Commonly used soil chemical extracts are not reliable when attempting to predict occurrence of the problem. Soil vesicular-arbuscular mycorrhizae (VAM) fungi have been shown to increase host plant uptake of relatively immobile nutrients like P. In studies of fallowed soils, VAM colonization rates are lower than similar unfallowed soils. Decreased VAM colonization rates appear to be a factor in development of the disorder. Corn (Zea mays L.) is probably the crop most susceptible to Fallow and Flooded Soil Syndromes. Phosphorus deficiencies have successfully been corrected using a starter P fertilizer applied in a band at planting. Broadcast fertilizer treatments have been ineffective on corn but effective for soybean [Glycine max (L.) Merr.].

Occurrence of vesicular-arbuscular mycorrhizae in Pseudotsuga menziesii and Tsuga heterophylla seedlings grown in Oregon Coast Range soils

Vesicular-arbuscular mycorrhizae (VAM) were common in seedlings of Pseudotsuga menziesii and Tsuga heterophylla grown in a greenhouse soil bioassay in soils collected from the Oregon Coast Range. Although root samples were heavily colonized by ectomycorrhizal fungi (EM), VAM colonization was observed in the cortical cells of both secondary and feeder roots. Vesicles, arbuscules, and hyphae typical of VAM occurred in 48% of 61 P. menziesii and 25% of 57 T. heterophylla seedlings. The ecological significance of VAM presence in the Pinaceae, as well as interactions among VAM, EM, and the plant host, deserve future investigation.

Mycorrhizal and common root-rot infection, and nutrient accumulation in barley grown on breton loam using N from biological fixation or fertilizer

This paper presents soil biological data from a study on the functioning of three soil-plant systems on a Gray Luvisol in Cryoboreal Subhumid central Alberta. The systems were (1) an agroecological 8-year rotation, (2) a continuous grain system, both established in 1981, and (3) a classical Breton 5-year rotation established in 1930. The objectives were to (1) determine whether changes in vesicular-arbuscular mycorrhizae (VAM) populations occurred in soil under these cropping systems, (2) discover whether these cropping systems and/or VAM infection influenced the incidence of common root rot (Bipolaris sorokiniana), and (3) use nutrient translocation indices to test the hypothesis that soil quality influences non-specific physiological conditions in barley (Hordeum vulgare L.). VAM fungal propagules in soil samples and VAM infection under controlled conditions were significantly affected by the cropping system. VAM infection accounted for more than 85% of the variability in grain yield, plant biomass yield, and plant uptake of K, S, Ca, Fe, and Zn under controlled conditions. Backward-elimination regression analyses showed that under these conditions of high available P, plant P uptake was governed by the quantity of extractable P in the soil (r2=0.82); the VAM infection contributed practically nothing when combined with available P (R2=0.84). Neither VAM infection nor the cropping system were related to the B. sorokiniana infection in the barley. The growth of B. sorokiniana was equal, and its sporulation superior, when grown on residues of the non-host fababean (Vicia faba L.), compared with growth on residues of barley. Higher translocation of plant nutrients to the grain in the agroecological compared with the continuous grain treatments suggested that VAM and/or the soil history affected plant physiology, possible through hormonal effects. Superior barley yields in the agroecological compared with the continuous grain treatments were partly due to increased VAM colonization, greater nutrient accumulation and translocation to the grain, but not to a reduced disease incidence. These results demonstrate the benefits of a holistic systems approach while studying biological interactions involving plants and groups of soil microorganisms.

Cropping Systems Effects on Mycorrhizal Colonization, Early Growth, and Phosphorus Uptake of Corn

AbstractA field study was established in 1986 on a Viborg silty clay loam (fine‐silty, mixed, mesic Pachic Haplustoll) soil in eastern South Dakota. The objectives were to quantify the influence of crop rotation, tillage, and residual P (254 kg P ha−1 applied in fall 1985) on the incidence of vesicular‐arbuscular mycorrhizae (VAM) of corn (Zea mays L.) and to define the relationship between VAM colonization, early growth response to P, and early P uptake of corn. Plant and root samples were collected periodically from plots that varied in tillage and previous crop. Crop rotation and tillage influenced the early growth and P uptake of corn. Large differences in early growth response to P were observed among cropping systems. Average relative growth response as compared with the check during both years ranged from 360% for the moldboard (MP) corn‐fallow rotation to 7% for the ridge‐plant (RP) corn‐soybean (Glycine max [L.] Merr.) rotation. Early dry‐matter production and P uptake in the check plots were highest in the RP corn‐soybean system and lowest in the MP corn‐fallow system. Generally, VAM colonization rates were significantly higher (P ≤ 0.10) in the RP systems than in the MP systems. Considerable reduction in VAM colonization rates were found with P fertilization (P ≤ 0.01) in all cropping systems. An inverse relationship was measured between VAM colonization and relative early growth response to P (Y = 647.0 − 49.4X + 0.97X2; R2 = 0.92; Y = growth response in percent, X = percent root length colonized). Considering early dry‐matter production, P uptake, and mycorrhizal association the RP corn‐soybean system appears to provide a good environment for P nutrition of corn during early vegetative growth.

Vesicular–arbuscular mycorrhizal ecology of little bluestem across a prairie–forest gradient

Changes in little bluestem (Schizachyrium scoparium) plant cover and vesicular–arbuscular mycorrhizae (VAM) root colonization, VAM spore density, and mycorrhizal inoculum potential were examined across a gradient from open sand prairie to closed oak–hickory forest in central Illinois. Soil samples were collected randomly and from the rhizosphere of little bluestem. Significant negative rank correlations were found between tree basal area and percent aerial cover of little bluestem, VAM colonization of little bluestem roots, mycorrhizal inoculum potential, and VAM spore abundance. However, spore abundances for randomly collected and rhizosphere soil samples, VAM colonization, and mycorrhizal inoculum potential had significant positive rank correlations with little bluestem cover. Highest spore densities were associated with the open sand prairie dominated end of the gradient, with lower spore numbers being found within the closed forest. Rhizosphere and randomly collected soil samples had a decrease in VAM fungal species richness as the vegetation types approached that of a closed forest community; however, dominant VAM fungal species were present throughout the gradient. Observed relationships between colonization, mycorrhizal inoculum potential, spore abundances, and little bluestem cover suggest interdependencies between host plant and associated mycobionts and (or) similar responses to environmental factors.

EFFECT OF GRAZING ON GROWTH, CARBOHYDRATE POOLS, AND MYCORRHIZAE IN WINTER WHEAT

Winter wheat (Triticum aestivum L.) was either subjected to fall grazing or left ungrazed and was examined the following spring for above and below ground growth, carbohydrate pools, and root length colonized by vesicular-arbuscular mycorrhizae (VAM). Root colonization by VAM occurred in both grazed and ungrazed winter wheat during reproductive growth (late spring). Prior to May, low soil temperatures apparently inhibited VAM colonization. Percent VAM colonization did not differ between treatments during reproductive growth, but root length per unit of soil volume was reduced by grazing, resulting in a greater colonized root length for ungrazed plants. Grazing reduced total carbohydrate pools. Although grazing and VAM colonization were separated in time, a grazing effect on colonization was evident. Colonization may be governed by the wheat plant’s ability to recover from grazing during the period prior to VAM spore germination. Although grazed plants gained more carbon during reproductive growth, the gain was not sufficient to overcome the grazing induced carbon limitation, as grain yields and VAM root length density were reduced by 16 and 38%, respectively.Key words: Wheat (winter), grazing, mycorrhizae, carbohydrates

Lack of Vesicular‐Arbuscular Mycorrhizal Inoculum in a Ponderosa Pine Forest

Comparison of live beetle—killed ponderosa pine stands revealed that understory biomass was higher under beetle—killed pines. Carex heliophila, a nonmycorrhizal plant, was virtually the only species present beneath live ponderosa pines. We examined the extent to which vesicular—arbuscular mycorrhizae (VAM) colonized understory plants on both live and beetle—killed pine sites; the availability of live— and killed—pine soil VAM inoculum in situ and in the laboratory; the abundance of VAM spores in field soils; and the possible inhibition of VAM formation by forest floor decomposition products in live—pine soils. Roots of field species from live and beetle—killed pine soils, as well as bioassay plants (species not native to the study site) grown in situ and in the laboratory were cleared, stained, and examined for presence or absence of VAM colonization. Sixty percent of the understory of live pine was composed of nonmycorrhizal species, 26% of mycorrhizal species, and 14% of species not examined for VAM. Twenty—nine percent of the understory of killed pine was composed of nonmycorrhizal species, 51% of mycorrhizal species, and 20% of species not examined for VAM. All laboratory bioassy plants were nonmycorrhizal in live—pine soils and mycorrhizal in killed—pine soils. No in situ bioassay plants became mycorrhizal beneath live pines. Counts of 50—250 μm VAM spores in May 1981 and August 1982 were 0.013 and 0.098 spores/g, respectively, in live—pine soils and 0.36 and 4.97 spores/g, respectively, in killed—pine soils. We found no evidence that VAM colonization in corn plants was inhibited by forest floor decomposition products. Mycorrhizal colonization of field species was greater in the killed—pine understory than in the live—pine understory. Laboratory and field studies showed that VAM inoculum was absent in the understory of live ponderosa pines. Allelopathic—type suppression, either of host plants or of the mycorrhizal colonization process, might explain the lack of inoculum. Direct inhibition of the colonization process, however, was not observed in greenhouse experiments.

THE MYCORRHIZAE OF PIONEER SPECIES IN DISTURBED ECOSYSTEMS IN WESTERN PENNSYLVANIA

Study plots with ten types of disturbances were established in a Solidago‐Aster community in western Pennsylvania. One year after disturbance, 93% of all species had vesicular‐arbuscular mycorrhizae (VAM) and accounted for 92% of all plant cover. After 3 yr, 96% of the species had VAM and 96% canopy coverage. An adjacent 10‐yr Solidago‐Aster community had 100% VAM species. The VAM annuals, Ambrosia artemisiifolia and Setaria glauca, were major first year dominants while VAM perennials, Agropyron repens, Solidago canadensis, and Aster ericoides, dominated at 3 yr. The mean percent mycorrhizae of all dominants at 1 yr was 39% and 34% at 3 yr. Four disturbed sites had 100% VAM colonization after 1 yr and six sites after 3 yr. Severe physical disturbances (topsoil removed and topsoil‐subsoil removed) resulted in complete colonization by VAM species and mean mycorrhizal infections of more than 75%. The plowed‐disked‐prometone and plowed‐disked‐vapam disturbances resulted in low levels of mycorrhizae after 3 yr. The plowed‐disked‐atrazine plot showed an initial severe decrease in percentage of mycorrhizae, but doubled its infection rate by 3 yr. Three non‐mycorrhizal species (Chenopodium album, Rumex acetosella, and Polygonuspersicaria) were observed during the 3‐yr period. C. album was the major dominant after 1 yr in the plowed‐disked‐fertilized site and R. acetosella a dominant in the plowed‐disked‐prometone plot.