Different methods for quantification of active extraradicular mycelium (AEM) and total extraradicular mycelium (TEM) of arbuscular mycorrhizal fungi (AMF) were examined by conducting an experiment under greenhouse conditions, with a completely randomized factorial design and five replicates per treatment. The experiment was arranged in a 4 x 6 x 2 design and the factors were: 3 species of AMF (Glomus intraradices, G. etunicatum and G. clarum) and one control without AMF x 6 levels of P (0, 50, 100, 150, 200 and 250 mg kg-1) x 2 citrus species (Citrus reshni and Citrus sinensis). Six months after transplanting, height and diameter were evaluated and the plants were harvested. Shoot dry weight, total shoot macronutrients, percentage of root infection and the length of AEM and TEM by the fluorescein diacetate (FDA) and the iodonitrotetrazolium reduction (INT) methods were also evaluated. Increasing levels of P promoted decreases in percentage of root infection and increases in plant height, diameter, dry weight and macro and micronutrients absorbed by both citrus species. There was a negative correlation between AEM and total macronutrients absorbed (P, N, Ca and Mg) by Citrus sinensis and a positive correlation between TEM and those macronutrients by C. reshni indicating that the latter host may be more mycotrophic than the former and, possibly, that there are other mechanisms of nutrient absorption rather than by AEM, with results varying in relation to the method used.
FDA; INT; vital stain