Adaptability of the fine root system of <em>Ceiba pentandra</em> (L.) Gaertn. to various sites of central Amazônia, Brazil

Ceiba pentandra (L.) Gaertn. (sumaúma), an economically important tree species in central Amazônia, stands out on account of its considerable ecological capacity of adapting to different site conditions. It can survive under seasonally dry conditions on terra firme as well as in the seasonally inundated várzea. Particularly the fine roots can structurally adapt to different soil conditions. The adaptation of the fine roots to terra firme condition results in the formation of an aerenchyma consisting of only small intercellular canals. During the dry months the walls of the epidermis cells increase in thickness and moreover they lignify and the exodermis suberize to prevent drainage. On the other hand the fine roots growing on várzea sites form lysigenously an aerenchyma consisting of extended and large intercellulars both within the cortex and the central cylinder. This large intercellular system supplies the plant with water and mineral elements and maintains the oxygen supply enabling photosynthesis throughout the year. In addition, above the soil surface numerous adventitious roots grow during the inundation period developing only small intercellular spaces within the cortex. Suberization is missing and only the primary xylem lignifies. A simulation of the fine root study under similar growth conditions in a tropical greenhouse completely confirmed the structural adaptations of the fine roots to dry and seasonally inundated conditions. This ecological amplitude is important for the selection of Ceiba pentandra for sustainably managed forestry systems.