Variability in Azolla sporulation in response to phosphorus application

Abstract

 Phosphorus application decreased the sporulation frequency and number of sporocarps per plant in all the three Azolla species and 21 A. pinnata strains evaluated in this study. The number of megasporocarps tended to be more depressed than the number of microsporocarps. Nevertheless, the sporulation of A. caroliniana was less sensitive to P than that of A. pinnata and A. microphylla. Its sporulation frequency in the mineral medium did not decrease at 2.5 μg P ml^–1 and remained unaffected between 5 and 20 μg P ml^–1. The sporulation frequency and sporocarp number in this species in the soil culture also were not significantly affected by an increase in the dose of P from 10.7 to 21.4 or 21.4 to 32.1 mg pot^–1. Large variations in the degree of inhibition of sporulation due to the application of P (21.4 mg pot^–1) also occurred among the A. pinnata strains tested.