Effect of Soil Water Status on the Physioecological Traits and the Ecological Replacement of Two Endangered Species, Changium Smyrnioides and Chuanminshen Violaceum

Abstract

Both Changium smyrnioides Wolff and Chuanminshen violaceum Shen et Shan are monotypic species of the family Umbellaceae. They have narrow distribution areas and can only be found in the Yangtze River basin in China. Changium is distributed from the east to middle subtropical zone of China, and Chuanminshen from the middle to the west; they almost meet in the middle of the Yangtze basin. Because the climate varies from humid to semi-humid, an experiment was carried out to find out the two species' demand for soil water and analyze their niche separation by determining changes in their physio-ecological and structural traits in response to different soil water statuses. Results showed that the two species have similar structural characters and functional intensity. Diurnal variations, daily mean values, and relationships of irradiation and temperature to PN, E and WUE among the three treatments indicate that Chuanminshen has more tolerance to drought than Changium. Changes in morphological traits also suggest that Changium adapts to medium to wet soil conditions while Chuanminshen adapts to drought soil conditions. The differences in the adaptation of physiological and morphological traits to the water environment should be part of the reason these two species have become geographically vicarious species. The results indicate that, at least, the mechanism and the approach to conservation for the two species are similar.