Observations on the Mycorrhizas of Forest Trees. II. The Rhizosphere of Pinus Radiata D. Don

Abstract

SummaryTwo common mycorrhiza types of Pinus radiata were examined by light and electron microscopy. Large numbers of bacteria and fungal species other than those forming the mycorrhiza as well as diatoms were observed in the mycorrhizosphere. Different morphological types of bacteria were characteristic of different mycorrhizal types, and in some cases the bacteria were associated with lysed regions of the mantle. The distribution of the bacteria within the rhizosphere is discussed in relation to the clay minerals and the carbohydrate and polyphenol metabolisms of the host.Within the mantle and the Hartig net, the hyphae have a structure typical of basidiomycetes, but within the tannin layer the hyphae have an abnormal distorted appearance. This is correlated with changes in cytology and is construed as evidence of the production of polyphenols toxic to fungi.. A possible role of these polyphenols in the control of mycorrhizal associations by selective action on soil fungi entering the rhizosphere is discussed.

Ultrastructural study of ectomycorrhizas on Pinus caribaea Morelet. var. hondurensis Barr. & Golf. seedlings

“…Distribution of glycogen-like rosettes in the hyphae was consistent with that found by several authors (Foster & Marks 1966;1967;Jordy et al 1998). Glycogen found in the mantle and Hartig net hyphae could be a result of seasonal variation (Duddridge & Read 1984;Genet et al 2000) and related to the physiological state of the association.…”

“…In this association carbon flows to the fungus, which absorb and translocate nutrients from the soil to the host plant (Sylvia et al 1997). The ultrastructure of many ectomycorrhizal forest tree species has been widely studied since the early works of Foster & Marks (1966;1967). Electron microscopy is a useful tool for cytochemical localization (Rincon et al 2001) and imunolocalization (Tagu et al 2001) allowing the researches to compare the ultrastructure of different types of ectomycorrhizas.…”

Matsutake – morphological evidence of ectomycorrhiza formation between Tricholoma matsutake and host roots in a pure Pinus densiflora forest stand

“…The mantle, host epidermal and outer cortical cells of Matsutake mycorrhizal roots contain a large number of darkly stained inclusions, consistent with Pinus ectomycorrhizas (Foster & Marks, 1966). The progressive blackening and subsequent necrosis observed from base to tip in type I through to type IV mycorrhizal roots, appears to be a result of infection and progressive root colonization.…”

Fungi Colonization of the Rhizoplane of Okra (Hibiscusesculentus) Plant

“…The fungi found around cultivated soil is quite different from uncultivated soil community purposely because growing plant creates a unique habitat for microorganisms and are inturn affected by their population. Relationship that occurred amongmicroorganisms, soil and roots were observed by Foster and Marks, (1967) through transmission electron microscopy (TEM) of the soil-root interface.The rhizoplane is the root surface of the plant (Rovira, 1965) and different from the rhizosphere which is the zone (soil) surrounding the plant root (Rovira, 1965).The Rhizoplane which is the root surface of the growing plants in the soil provide a unique habitat, the rhizosphere, which is particularly favourable for the development of the microorganisms in the soil. However, the majority of the microorganisms stimulated by rhizoplane are usually harmless saprophytes which live mainly on dead, decomposing root tissues.The root excretions such as volatile and dissolved exudates affect microbial growth in the root surrounding soil, also most microbial activities in the soil is associated with the roots or fresh decomposing organic materials, therefore, soil microorganisms including "Fungi" depend on available organic compounds for survival while activity of microorganisms in noncultivated soil will be dormant.It is claimed that the young root presents "a virgin niche" available for soil microorganism colonization and as the root grows through soil, the root exudates promote the fungal spores germination as a propagules and growth of fungal hyphae.…”