Relationships between lateral root order, arbuscular mycorrhiza development, and the physiological state of the symbiotic fungus in Platanus acerifolia

Abstract

The rapid development of an efficient root system resulting from arbuscular mycorrhiza formation is essential to the successful establishment of many plant species. We have analysed root system development and used histochemical staining to define relationships between lateral root order dynamics, arbuscular mycorrhiza development, and the physiological state of the symbiotic fungus Glomus fasciculatum (Thaxter sensu Gerdeman) Gerd & Trappe amend. Walker and Koske, in a woody plant species Platanus acerifolia Willd. Arbuscular mycorrhiza induced modifications in root system development in P. acerifolia, compared with nonmycorrhizal root systems. Third-order lateral roots dominated in arbuscular mycorrhizal plants, while second-order laterals were most numerous in nonmycorrhizal systems. Arbuscular mycorrhiza colonization was closely related to the appearance of different root orders; the most active mycelium (characterized by fungal succinate dehydrogenase and alkaline phosphatase activities) was mainly localized in newly formed lateral roots. Nine weeks after inoculation with G. fasciculatum the proportion of alkaline phosphatase-active mycelium strongly decreased in all root orders, and this was related to an increased phosphorus content of the host plant. The dynamics of development of the arbuscular mycorrhizal fungus and the possible regulation of its activity by the host plant are discussed. Keywords: arbuscular mycorrhiza, fungal enzyme, root system morphology, Platanus acerifolia, Glomus fasciculatum.