Summary
The productivity of three species of Azolla (A. pinnata, A. filiculoides andA. caroliniana) in outdoor culture has been evaluated at different planting densities. The highest yields were obtained with biomass concentration ranging from 40 to 70g d.w. m−2. The mean productivity over a 90 days period (from May 10th to August 10th) ranged from 10g d.w. m−2 day−1 forA. filiculoides up to 11.5 g d.w. m−2 day−1 forA. caroliniana. The nitrogen content of the dried biomasses was 48.3 mg (g d.w.)−1 forA. pinnata, 51.5mg (g d.w.)−1 forA. filiculoides and 52.3 mg (g d.w.)−1 forA. caroliniana. Very little variations of the nitrogen content of the ferns during the experimental period were observed.
The nitrogen-fixing efficiency of the Azolla-Anabaena azollae symbiosis grown in outdoor conditions was evaluated both by direct measurement of the amount of N2 fixed by the culture and by the C2H2-reduction and H2-evolution tests in an air atmosphere. These tests were performed outdoor under the same environmental conditions as the growing cultures. For all the species the ratios of C2H2-reduced to N2-fixed were unexpectedly low, ranging from 2.04 (A. pinnata) to 1.50 (A. caroliniana).
The results suggest that the reliability of the C2H2-reduction assay, particularly when applied to complex biological N2-fixing systems, must be re-examined.
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Vincenzini, M., Margheri, M.C. & Sili, C. Outdoor mass culture ofAzolla spp.: yields and efficiencies of nitrogen fixation. Plant Soil 86, 57–67 (1985). https://doi.org/10.1007/BF02185025
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DOI: https://doi.org/10.1007/BF02185025