Abstract:

Habitat preference has played an important role in the evolution of the genus Isoetes. Aquatic Isoetes species are generally distributed in oligotrophic softwater. However, it is still uncertain if chemical properties of the water have an impact on the pattern of distribution of Isoetes species. Investigation of habitat preference with regard to water chemistry in natural habitats of species would contribute significance to our understanding of evolution in the genus. Four species of Isoetes are known to occur in China: Isoetes taiwanensis in Taiwan island and I. hypsophila, I. yunguiensis and I. sinensis in the mainland, and their distribution regions do not overlap. All four species are endangered aquatic plants throughout their distribution range in the country.In this paper, 20 parameters of water chemistry in the natural habitats of three species of Isoetes in mainland China were measured, using HANNA Pocket-sized pH Meter HI98107 (resolution = 0.1 pH, accuracy = ±0.1 pH), HANNA Conductivity Meter Dist4/HI983004 (resolution = 0.1 m S·cm-1, accuracy = ±0.1 m S·cm-1) and HANNA C200 Multiparameter Ion Specific Photometer (resolution of NO3-N, NO3-, P, Mn and Mo = 0.1 mg·L-1, accuracy = ±0.1 mg·L-1；resolution of other factors = 0.01 mg·L-1, accuracy = ±0.01 mg·L-1). The character and variation of the chemical properties of the water were analyzed using mean, coefficient variability and difference significance tests (ANOVA and Kruskal-Wallis). Results showed a common character in that there were bigger variations in average and coefficient variability of the 20 parameters. Average Ni was overwhelmingly greater than the other factors, and lower conductivity indicated there was litter pollution in the water. However, of the 20 factors assessed, except for pH (p<0.05), P (p<0.05), NO3-N (p<0.05), NO3- (p<0.05) and Al (p <0.01), the rest displayed no significant difference among habitats of the three species. This indicated that most of the factors (75%) were relatively stable. pH had an identically positive correlation with NO3-N and NO3- (p<0.05); on the contrary, P had an identically negative correlation with NO3-N and NO3- (p<0.05). pH and P were also negatively correlated (p<0.05). Only Al had a positive correlation with P (p<0.05). An analysis, according to data from other research and this study, suggested the significant difference of chemical nature of the water among the three Isoetes species could be due to differences in physiological characters among them, and has no impact on their distribution.