Abstract: [Objective] To provide the fundamental scientific information on Azolla for preservation and study the effects of environmental conditions on the growth and ecological stoichiometry of the aquatic plants in the ecosystem. [Method] Using a soil water culture under a net cover (SWN) or a nutrient water culture in a greenhouse (NWG), the biomasses and ecological stoichiometric characteristics on C, N and P of 8 varieties of Azolla, including A. filiculoides lamarck, A. Mexicana Schlecht et cham, A. caroliniana Willd, A. microphylla Kaulf, A. imbricate (Roxb.) Nakais, A. pinnata R. Brown, A. microphylla Kaulf and A. microphylla Minyu No.1, were compared. [Result] In SWN, the biomasses and contents of C and N of all 8 varieties were higher than those in NWG, but the P contents were lower. The C:P and N:P ratios of the plants in SWN were higher than those in NWG, whereas, the C:N ratios were similar. Since the N:P ratios of all plants grown in either SWN or NMG were below 14, N was presumably the primary factor affecting the plant growth. [Conclusion] Cultivation in SWN appeared to be more conducive than NWG to the growth of Azolla plants. In addition, N seemed to be a crucial nutrient, more so than C or P, for the growth of Azolla.

Key words: growth environment, Azolla, C, N, P, ecological stoichiometry