CHANGES IN SUGAR LEVEL AND RELATED ENZYME ACTIVITY OF ARBUSCULAR MYCORRHIZAL ASPARAGUS

Changes in sugar levels in young asparagus seedlings that had been grown on soil supplemented with increasing levels of phosphate (0, 20, 100, 500 mgP2O5/g soil), with or without inoculation with Gigaspora margarita, were examined. Infection of feeder roots with the arbuscular mycorrhizal (AM) fungus at four weeks after inoculation was 63-78%, except in the case (32-34%) of seedlings grown on soil that contain a high concentration of phosphate. At the same time, sugar levels in various tissues (cladophyll, main stem, storage root and feeder root) of inoculated seedlings were equal to or lower than those of non-inoculated seedlings at comparable soil P. Both P fertilization and inoculation with AM fungus, separately or in combination, increased dry matter and decreased sugar levels, except in storage roots. In the storage roots, there was no significant negative correlation (P > 0.05) between dry weight and sugar levels. The activities of enzymes involved in carbon metabolism in asparagus plants were stimulated by AM colonization, enhancing formation of sugars for transport in the fern and accumulation in storage roots as fructans. The AM fungus only affected asparagus seedling sugar levels at the early stage of growth (four weeks after inoculation). Moreover, the reaction to colonization by the AM fungus differed among regions in terms of the promotion of growth of seedlings.