Analyses on soil nutritional status and water pH value in natural habitat of endangered plant Isoëtes orientalis

The content of main nutritional components in soil of natural habitat of two plots (Shupowan and Xiaolanhu in Songyang of Zhejiang Province) of Isoëtes orientalis H. Liu et Q. F. Wang was comparatively analyzed, and the pH value of water in plot of Shupowan was determined. On this basis, the factors of soil and water led to I. orientalis endangered were discussed. The results show that contents of organic matter, total nitrogen, available phosphorus, available potassium and total iron ions (including Fe 3+ and Fe 2+) in soil of Shupowan are 102. 7 g · kg -1, 3.1 g · kg -1, 18.1 μg · g -1, 15.0 μg · g -1 and 221. 6 μg · g -1, respectively, and those in soil of Xiaolanhu are 122. 8 g · kg -1, 4. 8 g · kg -1, 13. 7 μg · g -1, 7. 1 μg · g -1 and 240.0μg · g -1, respectively. The contents of organic matter, total nitrogen and available potassium in soil of Xiaolanhu are significantly or very significantly higher than those of Shupowan, while the content differences of available phosphorus and total iron ions are not significant between two plots. But the available potassium content in soil of two plots is very low, while the total iron ion content is rich. The water pH values in upper, middle and down streams of Shupowan are pH 6. 35, pH 6.53 and pH 6.49, respectively, showing approximately neutral. It is suggested that the soil type in the two natural plots is the type which the contents of organic matter, total nitrogen, available phosphorus and total iron ions are rich, and the available potassium content is low. And extreme lack of available potassium in soil and water neutralization are probably the important environmental factors to limit development of I. orientalis population.