External hyphae of vesicular‐arbuscular mycorrhizal fungi associated with Trifolium subterraneum L.

Abstract

SUMMARYVariation among VA mycorrhizal fungi in their ability to enhance phosphorus uptake and plant growth could be due to differences in the length, distribution and phosphorus uptake of external hyphae. Trifolium subterraneum L. was grown in a sandy soil in association with the VA mycorrhiza] fungi Acaulospora laevis Gerdemann & Trappe, Glomus sp., Scutellospora calospora (Nicol. & Gerd.) Walker & Sanders or left uninoculated. When mycorrhizas had become well established, plants were transferred to a two-compartment system, where root growth into a hyphal compartment was restricted by a fine nylon mesh. Spread of hyphae into the hyphal compartment was monitored by sequential sampling of soil cores at difFerent distances from the root compartment. Plants were harvested at three times.The spread of hyphae differed between fungi. The length density of hyphae of S. calospora declined approximately exponentially with increasing distance from the roots, whereas A. laevis maintained a plateau of constant hyphal density up to 7 and 11 cm from the roots after 28 and 47 d, respectively. Glomus sp. had an intermediate pattern of spread with a plateau closest to the roots followed by an exponential decline. The average rate of hyphal spread (mm d"') was 3-1 for A. laevis but only 0'7-0-8 for Glomus sp. and S. calospora. In addition to its more extensive hyphal spread, A. laevis produced the largest increases in phosphorus uptake and plant growth. All mycorrhizal plants had a larger phosphorus inflow than the non-mycorrhiza! controls, but the phosphorus inflow per unit mycorrhizal root length was 2-5-3 times as high with A. laevis as with the two other fungi. These differences between the fungi became even more pronounced when the phosphorus inflow was expressed on the basis of hypha! length.This work indicates that the efficiency of phosphorus uptake by a VA mycorrhizal fungus is strongly affected by its spatial distribution of hyphae in the soil, and possibly also by differences in capacity for uptake by unit length of hypha.

The arbuscular mycorrhizal fungus Glomus mosseae can enhance arsenic tolerance in Medicago truncatula by increasing plant phosphorus status and restricting arsenate uptake

“…Phosphorus was determined by the molybdenum blue method (Allen, 1989) and As using a Model AFS-920 Atomic Fluorescence Spectrometer (Beijing Titan Instruments Co. Ltd.). The extraradical mycelium was extracted from three replicate w7-g sub-samples of soil from each pot using the aqueous membrane filtration technique (Boddington et al, 1999) and hyphal length was estimated using a modified membrane filter technique (Jakobsen et al, 1992).…”

Chromium immobilization by extraradical mycelium of arbuscular mycorrhiza contributes to plant chromium tolerance

“…ERM in RC and HC were extracted from soil samples using a modified membrane filter technique (Jakobsen et al, 1992). Briefly, the soil samples were mixed and 4 g of the samples were blended with 250 mL deionized water, hyphae in 5 mL aliquots were then collected on 25 mm membrane filters (0.22 mm) and stained with 0.05% Trypan blue.…”

Effects of the mycorrhizal fungus Glomus intraradices on uranium uptake and accumulation by Medicago truncatula L. from uranium-contaminated soil

“…Percentage root colonization and root length were determined by the grid line intersect method (Giovannetti and Mosse, 1980). External hyphae were extracted from soil samples using a modified membrane filter technique (Jakobsen et al, 1992). …”