The response of Anabaena-free Azolla and the symbiotic Azolla to temperature

Abstract

The performance of Anabaena-free (algae free) and symbiotic types of three speeies of Azolla (A. filiculoides, A. pinnata and A. microphylla) were studied in a phytotron at two average temperatures (22 and 33 ^oC). The growth of both the Anabaena-free and symbiotic types were depressed at a high temperature (33 DC) to varying degrees for all species of Azolla tested. There was a marked reduction of both growth and nitrogen-fixing ability (pereent N) of the symbiotie Azalia compared to its Anabaena-free counterpart suggesting that the low tolerance of A. jiliculoides No.1 0 I to high temperature was probably dictated by the symbiont Anabaena azollae. A. azollae of both A, microphylla No. 418 and A, pinnata No.2 appeared more tolerant to high temperature than that of A. filiculaides No. 101.