Growth, pigmentation and nitrogen fixation in Azolla spp. cultivated under four light flux denstms

Abstract

The effects of light flux densities (30, 50, 70 and 100% of sunlight) under growth, nitrogen fixation, pigmentation and shade adaptation were evaluated in three Azolla species (A. microphylla, A. carofniana and A. pinnata). These species showed maxima daily growth rates (G_m) and mínima duplication time of phytomass (T_d) by the 8^th day following inoculation under all light levels, except A. pinnata under full exposure in which G_m was reached by the 12^th day and minimum T_d by the 10^th day after inoculation. Under full sunlight, A. microphylla exhibited higher values of nitrogen fixation rates and anthocyanin content than A. caroliniana while A. primata showed minimal values of these parameters and maximal values at 50% of sunlight. A. microphylla showed to be more adapted to full sunlight followed by the A. caroliniana, A. pinnata, however, was more adapted to 50% of sunlight. Anthocyanin content increased and chlorophyll content decreased with the increment in light flux density on the superficial plants; moreover, the change in leaf pigmentation was not observed in the plants bellow this level.