Master of Science
Robert W. Fisher
The symbiotic association between the aquatic water fern Azolla and its symbiont, Anabaena azollae Straus. has been extensively studied in the past ten years. The cyanobacteria has received much of the attention due to its ability to fix atmospheric nitrogen while the fern free of the cyanobiont has been somewhat neglected. The purpose of this research was to determine the nutritional requirements of the cyanobacteria free (CBF) ferns and study the morphology of the leaves and branches of these CBF ferns.
Azolla filiculoides and Azolla pinnata were freed of the cyanobiont using the surface sterilization technique adopted from Duckett, et al. (1975) and the antibiotic treatments of Peters and Mayne(1974a). The size of leaf seven, both length and width, along with leaf spacing and branch spacing along the stem, in CBF ferns were compared to that in the intact ferns. Growth studies on medium containing three levels of the nutrients nitrogen, phosphorus and potassium were conducted.
The CBF ferns were found to have shorter leaves with no difference in width. The leaf spacing and branch spacing in the CBF ferns were more compact than the intact association. This is the first reported quantitative data to show a definite difference in the morphology of the CBF ferns. The nutrient studies showed an interaction effect between nitrogen and phosphorus in the A. pinnata CBF ferns while the A. filiculoides CBF ferns showed a nitrogen, phosphorus, potassium interaction. The A. pinnata CBF ferns grew best on a medium containing twice the concentration of phosphorus, one times the concentration of nitrogen and three times the concentration of potassium found in our I+ medium. The A. filiculoides CBF ferns grew best on concentrations of twice phosphorus, half nitrogen and three times potassium found in our I+ medium.
The results of this research shows the importance of phosphorus to the growth of the CBF ferns. This has been demonstrated in the intact fern association by Subudhi and Watanabe (1981). The results of the morphological studies indicate that either the cyanobiont, by its presence or through secretion of some substance affects the intact ferns growth and that this change can not be completely removed by the addition of specific nutrients to the medium.
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