A. Vilariño

Chitin and ergosterol content of extraradical and intraradical mycelium of the vesicular-arbuscular mycorrhizal fungus Glomus intraradices

Abstract A greenhouse experiment was carried out in order to compare microscopic estimations of hyphal length with chitin or ergosterol content of the vesicular-arbuscular mycorrhizal fungus (VAMF) Glomus intraradlces Schenck & Smith. Red clover (Trifolium pratense L.) either inoculated or not with G. intraradices was grown in 30 ml plastic cylinders referred to as inoculum compartments (IC) containing the inoculum. The bottom of the IC was removed and substituted with a 40 μm nylon net which allowed the passage of mycorrhizal mycelia but prevented roots passing through. Two ICs were placed in a larger 200ml pot filled with washed sand of particle size ranging from 100 to 1000 μm. This design provided a root-free substratum (RFS) surrounding the IC from which VAM mycelia were collected using the extraradical mycelium extraction (EME) technique. The mycelia collected were used for chitin and ergosterol analysis and the mycelial length was also determined. Root colonization, chitin and ergosterol content in roots were also determined. Correlations were found between the two biochemical parameters (ergosterol and chitin content) and hyphal lengths in the RFS. Mycelial lengths in the RFS averaged 4.3 m g−1 growth medium. The concentration of chitin and ergosterol in extraradical mycelia collected from the RFS averaged 0.29 μg m−1 and 0.24 ng m−1, respectively. Considerably higher values of both substances were obtained from colonized roots growing in the IC, averaging 5.7 mg chitin g−1 root dry wt and 11.09 μg ergosterol g−1 root dry wt, indicating that most of the mycorrhizal biomass is located within the root domain. The advantages and disadvantages of each method for quantifying extraradical VAM mycelia are discussed.

Numbers and viability of vesicular-arbuscular fungal propagules in field soil samples after wildfire

Abstract At two N.W. Spanish sites affected by forest fires during the summer of 1988. burnt plots and neighbouring control plots were sampled every 4 months during the following year to study (a) the effect of burning on the vesicular-arbuscular (VA) fungal propagules present in the soil. and (b) the colonization of the post-fire vegetation by VA fungi. The burnt plots had lower viable propagule densities than the control plots, as measured by the most probable number method and by spore counts, and VA colonization of the post-fire herbaceous vegetation (grasses) was less intense on burnt plots than on control plots. Spores of Acaulospora laevis (the species that dominated before burning) had lower germination rates when collected from the burnt plots than from the unburnt plots, and 1 yr after burning A. scrobiculata was the dominant species on burnt plots at the site with the steeper slope.

An instrumental modification of Gerdemann and Nicolson's method for extracting VAM fungal spores from soil samples

An easily constructed apparatus for extraction of VAM fungal spores from soil samples by a modification of Gerdemann and Nicolsons wet sieving and decanting method is described. For the soils employed in this study, it proved considerably more effective and more precise than either the original wet sieving and decanting method or differential water/sucrose centrifugation. The apparatus gave results that were less subject to interference from extraneous particles than the wet sieving and decanting method. The effect of prior soil dispersion is also reported.

'Fine' and 'coarse' mycorrhizal fungi on red clover plants in acid soils: Root colonization and plant responses

Three sterilized acid soils were inoculated with inocula of vesicular-arbuscular mycorrhizal fungi. Soils were limed and/or P fertilized to produce different fertility levels. Most inocula consisted of mixtures of ‘fine’ + ‘coarse’ type endophytes. Red clover (Trifolium pratense L.) was seeded in pots and grown in a glasshouse for 4 months. Root colonization by VAM fungi, the relative infection byGlomus tenue compared to that by ‘coarse’ VAM fungi and the effect of inoculation on red clover growth and mineral nutrition (P, K, Ca and Mg) were studied. Spores were also checked and tentatively identified.Results showed that root colonization by VAM fungi was higher than 50% in most cases, the lower values being found in the soil with the highest P content. Inocula containingG. mosseae + G. tenue infected plant roots only in limed (pH>5.7) soils. A study of the relative colonization by ‘fine’ and ‘coarse’ endophytes showed that the competitive ability againstG. tenue followed the orderG. fasiculatum > G. mosseae > G. epigaeum > G. macrocarpum, although soil properties and fertility were crucial factors.Glomus lacteum was tentatively identified in two of the three experimental soils. The inoculum in whichGlommus tenue was most infective was also the most efficient in improving plant growth and nutrient uptake. The effect of inoculation on P and Mg uptake followed a similar pattern.

Growth, micronutrient content and vesicular-arbuscular fungi infection of herbaceous plants on lignite mine spoils: A greenhouse pot experiment

A greenhouse experiment was carried out to determine the growth, micronutrient content and vesicular-arbuscular mycorrhizal (VAM) colonization of fescue and clover plants growing on a composite lignite mine soil. Five VAM fungus inocula were used. Results show that mine spoils had a high potential acidity and poor physical and chemical conditions for plant growth. Toxic levels of Al, Mn and Zn were found in plant tissues, with fescue showing apical necrosis. Glomus deserticola was the only VAM fungus that succeeded in colonizing plant roots, although it failed to improve the establishment or development of either species.

Changes on the development ofAcaulospora scrobiculata inTrifolium pratense (red clover) roots and bulk substrate after plant burning

In a pot experiment, burning or clipping ofTrifolium pratense plants colonized by the vesiculararbuscular mycorrhizal (VAM) fungusAcaulospora scrobiculata increased the number of spores in the substrate and the abundance of vesicles. The length of external mycelium and inoculum potential increased with clipping, but decreased with plant burning. Results suggest that the loss of photosynthesising tissue does not explain the effect of burning on VAM propagule activity. ei]R O D Dixon