Three ectomycorrhizal (ECM) isolates of Rhizopogon luteolus, R. roseolus and Scleroderma citrinum were found to differ markedly in their in vitro tolerance to adverse conditions limiting fungal growth, i.e. water availability, pH and heavy metal pollution. S. citrinum was the most sensitive, R. luteolus intermediate and R. roseolus the most tolerant species. Pinus radiata D. Don seedlings were inoculated in the laboratory and in a containerised seedling nursery with spore suspensions of the three ECM species. Colonisation percentage was considerably lower under nursery conditions, probably due to competition by native fungi. The effects of nursery ECM inoculation on seedling growth depended on the fungal species. Only R. roseolus-colonised plants showed a significantly higher shoot growth than non-mycorrhizal plants. All three fungi induced significantly higher root dry weights relative to control plants. Despite the low mycorrhizal colonisation, mycorrhization with all three species improved the physiological status of nursery-grown seedlings, e.g. enhanced root enzyme activity, shoot nutrient and pigment content, net photosynthesis rate and water use efficiency. Of the three fungal species, R. roseolus was the most effective; this species was also the most adaptable and showed the greatest range of tolerance to adverse environmental conditions in pure culture. It is, therefore, proposed as a promising fungal species for ECM inoculation of P. radiata in the nursery.
La reproducción de enzimas extracelulares por las ectomicorrizas moviliza una fracción importante de los compuestos presentes en el suelo. Se presentan resultados de las actividades enzimáticas relacionadas con la movilización de nitrógeno y fósforo para cuatro especies de hongos formadores de ectomicorrizas, Suillus luteus (L.: Fr.) F. Gray, Xerocomus badius (Fr.:Fr.) Gilbert, Boletus pinicola (Vitt.) Venturi y Pisolithus tinctorius (Pers.) Coker & Couch. Se considera el valor potencial de las actividades enzimáticas como criterio en la selección de hongos inoculantes. Los valores altos suponen una mayor utilidad de los hongos corno inoculantes en condiciones de vivero.
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