Vesicular-arbuscular Mycorrhizal Colonization Of Roots Research Articles

Mineralization of nitrogen from crop residues and N recovery by maize inoculated with vesicular-arbuscular mycorrhizal fungi

Legume crop residues serve as a source of nitrogen (N) for succeeding crops in low-input production systems, and characterizing the release of this N supports efforts to develop sound economic and environmental management practices. Nitrogen mineralization of 15N-labelled field crop residues was monitored in a Greenville sandy loam during a 140-day laboratory incubation at 25°C. Residue type strongly influenced the rate of N mineralization; decomposition rate constants were 0.283, 0.083, 0.00047 and 0.0014 day-1 for alfalfa (Medicago sativa L.) stover (above-ground plant parts), alfalfa roots, maize (Zea mays L.) stover (above-ground plant parts excluding cob and kernels) and maize roots, respectively. At the end of the incubation, 50% of alfalfa stover and 25% of alfalfa root residues N were mineralized, whereas these proportions were 8% for maize stover and 12% for root residues. Mineralization of 15N from alfalfa stover residues was also monitored in a greenhouse experiment to determine N availability during the growth of maize inoculated or not with vesicular-arbuscular mycorrhizal (VAM) fungi, and to evaluate the effects of the presence of plants on the decomposition of the residues. Stover and root dry matter yields were greatest for maize inoculated with VAM fungi and grown in residue-amended soil. At the final harvest, maize grown in residue-amended soils had accumulated 44% more dry matter and 40% more N than maize grown in unamended soils. Enhanced VAM colonization of roots inoculated with a mixture of three Glomus spp. increased the residue N accumulation in maize roots at 5 weeks after silking and at the final harvest. Alfalfa stover decomposed rapidly both in the presence and absence of maize plants, but the amount of 15N mineralized at the end of the experiment was influenced by the presence of living roots; 23% of the 15N in alfalfa stover residues was mineralized in soil without plants compared to about 38% when maize plants were present. These results suggest that N mineralization is enhanced by the presence of living roots.

Earthworm Aporrectodea trapezoides had no effect on the dispersal of a vesicular-arbuscular mycorrhizal fungi, Glomus intraradices

We investigated the interactions between earthworms and vesicular-arbuscular (VA) mycorrhizal fungi. The effects of earthworms ( Aporrectodea trapezoides) at three densities, on the initiation of mycorrhizal colonization of roots of Trifolium subterraneum L. were examined in Experiment 1. An increasing density of earthworms was associated with a decrease in proportional colonization of the roots by mycorrhizal fungi, with a significant difference between the treatment with no earthworms and that with three earthworms per pot (equivalent to 500 earthworms m −2). Experiment 2 was established to examine the effect of earthworms on the lateral spread of VA mycorrhizal fungi from localized inoculum through a sward of T. subterraneum. A reduction in colonization was again observed at 14 and 21 days (Experiment 2A) or 14 and 28 days (Experiment 2B) but was not evident at a later harvest. The effects of earthworms on the infectivity of an established fungal hyphal network was examined in Experiment 3. The mean proportional colonization was consistently lower in the earthworm treatment compared to the no-earthworm treatment, except in the 1–3-cm section of soil, but none of the differences was statistically significant. We obtained no evidence that earthworms increase the rate of spread of mycorrhizal fungi between plants. Our results indicate that earthworms reduce the infectivity of the soil, with respect to VA mycorrhizal colonization of roots. However, the reduction may only be transient. Possible mechanisms for this effect include grazing on or disturbance of the hyphal network in soil.

Plant and soil responses to mycorrhizal fungi and rhizobacteria in nodulated or nitrate-fertilized peas (Pisum sativum L.)

Rhizosphere organisms affect plant development and soil stability. This study was conducted to determine the effects of a vesicular-arbuscular mycorrhizal (VAM) fungus [Glomus mosseae (Nicol. &>; Gerd.) Gerd. and Trappe] and a rhizobacterium (Bacillus sp.) on nitrate-fertilized or nodulated pea (Pisum sativum L.) plants and on the status of water-stable soil aggregates. The plants were grown in pots in a yellow clay-loam soil, and inoculated with the VAM fungus and the rhizobacterium, with one of the two, or with neither. The Bacillus sp. and G. mosseae did not affect shoot dry mass in nodulated plants. Under N fertilization, the VAM fungus enhanced plant growth, while the rhizobacterium inhibited shoot growth, VAM root colonization, and nodule formation, but enhanced the root:shoot and the seed:shoot ratios. The inhibition of shoot growth and of root colonization appeared to be related. The water stability and pH of the VAM soils were higher than those of the non-VAM soils. The rhizobacterium enhanced the water-stable aggregate status in the non-VAM soils only. Under both N-nutrition regimes, the soils had the greatest proportion of the water-stable aggregates when inoculated with both rhizo-organisms and the lowest when colonized by neither. The two rhizo-organisms affected both plants and soil, and these effects were modified by the source of N input through N2 fixation or fertilization.

Wheat Responses to Vesicular‐Arbuscular Mycorrhizal Fungal Inoculation of Soils from Eroded Toposequence

AbstractLow fertility of eroded soils is often attributed to the loss of topsoil, an important source of nutrients for microorganisms and plants. Vesicular‐arbuscular mycorrhizal (VAM) fungi are known to improve nutrient uptake by plants from infertile soil. The objective of this study was to determine whether wheat (Triticum aestivum L.) responses to VAM fungal inoculation differ among eroded and noneroded soils from the same toposequence. Spring wheat plants were grown under growth chamber conditions in soils collected from three landscape positions of a typical toposequence in eastern Washington, with and without VAM fungal inoculation. Noninoculated soils exhibited 13 to 26% VAM root colonization, while inoculation increased VAM colonization up to 49 to 55% by 5 wk after planting. The VAM fungal inoculation of eroded soils increased shoot dry weight and tiller number, advanced the leaf stage, and increased root length compared with the noninoculated controls. Shoot concentrations of P and Zn were increased by VAM inoculation. In contrast, shoot concentrations of Cu and Mn were unchanged, while Fe was decreased. While VAM fungal inoculation also increased P, Zn, and Cu concentrations in water‐stressed plants, Mn and Fe concentrations decreased. No responses to VAM fungal inoculation were observed in soil from a noneroded toeslope, although VAM colonization was similar to that observed in the eroded soils. These results indicate the potential role of VAM fungi for improving dryland wheat productivity on eroded soils.

Residual toxicity of soil-applied chlorothalonil on mycorrhizal symbiosis in Leucaena leucocephala

The residual effect of the fungicide chlorothalonil on the vesicular-arbuscular mycorrhizal (VAM) symbiosis was evaluated in a greenhouse experiment. The soil used was an oxisol (Tropeptic Eutrustox) treated with P to obtain target levels near-optimal for VAM activity or sufficient for nonmycorrhizal host growth. In the uninoculated soil treated with the former P level, the fungicide reduced VAM colonization of roots and completely suppressed symbiotic effectiveness measured in terms of pinnule P content. When this soil was inoculated with Glomus aggregatum, symbiotic effectiveness was significantly reduced but not eliminated by 50 mg of the fungicide kg−1. At higher chlorothalonil levels, VAM effectiveness but not VAM colonization was completely suppressed in the inoculated soil. The pattern with which chlorothalonil influenced tissue P content and dry matter yield at the time of harvest closely paralleled its effect on VAM effectiveness. In the soil treated with P level sufficient for nonmycorrhizal host growth, the adverse effect of the fungicide on the above variables was appreciably milder than when the host relied on VAM fungi for its P supply. The toxic effect of the fungicide, therefore, was partly offset by P fertilization, suggesting that VAM fungi were more sensitive to chlorothalonil than the host. Our results demonstrate that although the toxic effect of chlorothalonil declined as a function of time, a significant level of toxicity persisted 12.5 weeks after the chemical was applied to soil.

Effect of aromatic plant species on vesicular-arbuscular mycorrhizal establishment in Pistacia terebinthus

The inoculation of Pistacia terebinthus with vesicular-arbuscular mycorrhizal (VAM) fungi and the spread of the infection were studied using a mixed cropping system, under glasshouse conditions, with Salvia officinalis, Lavandula officinalis and Thymus vulgaris colonized by Glomus mosseae as an inoculation method. This method was compared with soil inoculum placed under the seed or distributed evenly in the soil. Indirect inoculation with all the aromatic plants tested significantly increased VAM root colonization of P. terebinthus compared with the use of soil inoculum, although the effect on plant growth was different for each one of the aromatic species used as inoculum source. Inoculation with L. officinalis and T. vulgaris were the best treatments resulting in high VAM colonization and growth enhancement of P. terebinthus.

The relationship between vesicular-arbuscular mycorrhiza and lime: Associated effects on the growth and nutrition of brachiaria grass (Brachiaria decumbens)

We studied the effects of limining on growth and nutrient concentrations of Brachiaria decumbens inoculated with five vesicular-arbuscular mycorrhizal (VAM) fungal assemblages which orginated from soils with different acidity. Liming increased plant growth when applied at rates up to 3 g kg-1 soil and depressed growth at higher rates. Mycorrhizal plants grew better than non-mycorrhizal ones in unlimed soil and also liming rates of 4.5 and 6.0 g kg-1 soil. The growth amelioration effects of VAM in highly acid or over-limed soils were related to nutrient uptake. VAM fungi isolated from an acidic soil exhibited a high symbiotic effectiveness and were better adapted to unlimed soil than those that originated from non-acidic soils. VAM root colonization, 90 days after planting, was little affected by liming. Fungal spore production and species compositions were highly affected by liming. A mixture of Glomus diaphanum and Glomus occultum predominated in unlimed soils inoculated with VAM assemblages isolated from non-acidic soils. In these fungal assemblages, an increased liming rate favored Glomus etunicatum over the other VAM fungi. Gigaspora margarita sporulated abundantly when introduced into unlimed soils, but rarely in limed soils. VAM appear to be crucial for the establishment of brachiaria pastures in the nutrient-deficient acidic soils of Central Brazil. It is suggested that liming may cause striking shifts in VAM populations which may, in turn, have a long-term impact on agricultural productivity in the tropics.

Interaction of Glomus species and Vigna unguiculata in an oxisol subjected to simulated erosion.

An experiment was conducted in the greenhouse to determine the effectiveness of three species of vesicular-arbuscular (VA) mycorrhizal fungi in an oxisol subjected to simulated erosion using cowpea [Vigtta unguiculata (L.) Walp, cv.'California Black Eye'] as an indicator host. Inoculation of the eroded soil resulted in increased VA mycorrhizal colonization of roots without enhancing shoot P concentration and dry matter yields. Inoculation of the uneroded soil, however, led to significant improvement in infection level as well as in symbiotic effectiveness. Based on the results of this study, it appears that the lack of expression of mycorrhizal effectivness in the eroded soil is a result of nutrient deficiency. The results thus suggest the importance of restoring lost nutrients before the benefits of VA mycorrhizal inoculation could be effectively exploited for a successful establishment of a mycorrhizal cowpea in eroded soils.

Impact of simulated erosion on the abundance and activity of indigenous vesicular-arbuscular mycorrhizal endophytes in an Oxisol

The influence of simulated erosion on the abundance and activity of indigenous vesiculararbuscular mycorrhizal (VAM) populations was evaluated in an Oxisol. Surface-soil losses in excess of 7.5 cm were generally associated with significant decreases in the numbers of total and active VAM propagules and in the symbiotic effectiveness of the active propagules. Surface-soil removal not exceeding 7.5 cm was associated with decreased propagule abundance without adverse effects on VAM colonization of roots and symbiotic effectiveness of the fungi. The extent of VAM colonization of roots and the degree of symbiotic effectiveness observed at this level of simulated erosion were significantly higher than those observed in the soil not subjected to simulated erosion. This stimulation is attributed to the removal of antagonistic biotic factors as the top 7.5 cm of soil was removed. It is concluded that propagules lost during erosional soil losses must be replaced before legumes grown on relatively highly weathered and severely eroded tropical soils could appreciably benefit from the VAM symbiosis.

Effect of seed inoculation with yeast on root colonization by native vesicular-arbuscular mycorrhizal (VAM) fungi and symbiotic parameters of legumes under potted soil conditions

Summary Seed inoculation of various legumes with yeast significantly increased root colonization by native VAM fungi. The pigeon pea ( Cajanus cajan ) var. Pusa-78 was recorded for higher VAM root colonization both in the presence or absence of yeast inoculation as compared to other crops. Symbiotic parameters (nodule number, dry weight of shoot and root) of the crops were also increased, significantly due to yeast inoculation.

Vesicular–arbuscular mycorrhizal fungi associated with native tall grass prairie and cultivated winter wheat

More vesicular–arbuscular mycorrhizal (VAM) fungal species and significantly more fungal spores were recovered from undisturbed prairie soils than four winter wheat field soils in Kansas through the 1980–1981 growing season. Two previously undescribed sporocarpic species of Endogonaceae were found in prairie samples but have not been successfully established in pot culture, leaving the genus to which they belong unclear. Though variable, 11–50% VAM root colonization was evident in all prairie grass roots sampled throughout the year. In contrast, no identifiable VAM root colonization was evident in wheat until May after flowering when 27% root colonization was observed. During the 1981–1982 growing season, roots of two other wheat fields were sampled with similar results. No colonization occurred until May when 8% root colonization was evident. The possible influence of such low levels of root colonization occurring quite late in the growing season of winter wheat is discussed.