Colonization of fine roots of mahogany (Swietenia macrophylla King) by vesicular-arbuscular mycorrhizal fungi under plantation conditions in Central Amazon

Mahogany (Swietenia macrophylla King) is one of the most important commerci al tree species in tropical Northern Brazil and its timber is highly valued world-wide. Due to the massive exploitation in the past decades, however, mahogany supplies have diminished to the point that the Brazilian governmen t has recently ordered a complete harvesting stop. To counter the threat to its survival, intensive efforts were started in the past years to study fu ndamentals for sustainable management plantations of this species. In this context, the colonization of the fine roots by mycorrhizal fungi in plantation trees and seedlings raised in nurseries is of great importance for sustainable growth. In order to study the environmental requirements of mahogany, experimental plantations were established 1991 to 1993 on the po or latosol sites of the "terra firme" near Manaus/Amazon. Without exception , mycorrhiza developed intensively under plantation conditions and also in the 20-month-old seedlings cultivated under controlled conditions. Mycorrhizal structures of the Arum-type vesicular-arbuscular mycorrhiza (VA M) were found, with appressoria penetration and coiled hyphae, vesicles and arbuscules. The colonization of the fine roots with mycorrhizal fungi was restricted to the root zone with an active rhizodermis where suberization a nd a U-shaped secondary wall including lignification of the exodermis was n ot yet developed. From the secondary stage of the exodermis onwards the upt ake of water and mineral elements is maintained by specialized passage cell s. This adaptation strategy to the specific conditions of a dry season is s een as a characteristic feature of the fine roots of Swietenia macrophylla. Considering also the results of parallel investigations on the fine root st ructure, the water and mineral element cycling, and photosynthesis, mahogan y can be recommended for sustainable production of high-quality timber unde r plantation conditions.