The Research On Photosynthetic Physiology And Habitat Characteristics Of Isoetes Sinensis Palmer In China

Isoetes sinensis Palmer is an aquatic or amphibious primitive vascular plant species which is classified in the subdivision Lycopsida and occupies a very important position in the evolutionary history of the pteridophytes. In recent times Isoetes sinensis has declined rapidly in population quality and even disappeared from many locations in Mainland China. It is now considered to be rare and endangered in China and listed as a first category protected plant species. The progressive decline in populations of Isoetes sinensis in Mainland China has been attributed to on-going anthropogenic changes, however, no data have been adduced to support this assumption. In present dissertation, the locations that presently have populations of Isoetes sinensis and locations from where the species has previously been sighted but now extirpated have been investigated. The habitat characteristics including elevation, water physical and chemical characteristics and the conditions of water substrate were measured in each site. The natural distribution and status of every current population of Isoetes sinensis were recorded. Plants of Isoetes sinensis and the associated species were collected. The characteristics of crassulacean acid metabolism (CAM) occur in Isoetes sinensis were also studied in experimentalconditions. The aims of this study are to approach the endangered mechanism of Isoetes sinensis from the angle of physiological ecology and provide scientific basis to the conservation of Isoetes sinensis. The main conclusions are as follows:1.) Isoetes sinensis distributes mainly in the lower and middle reaches of the Yangtze River and the Qiantangjiang River basin in Mainland China and grows mainly in aquatic or wetland habitats in shallow alpine pool or abandoned field meadow moor or freshwater tidal river eulittoral zone at elevation from 10 m to 1300 m. At present, only five natural populations of Isoetes sinensis were found in Xiuning of Anhui province, Jiande and Songyang of Zhejiang province in Mainland China. The natural distribution of Isoetes sinensis is discontinuous and every population of Isoetes sinensis is insulated from other populations. The individuals of every population of Isoetes sinensis are few and belong to mini-population.2.) The natural distribution and occurrence of Isoetes sinensis plants in Mainland China are closely correlated with its habitat characteristics including water physical and chemistry characteristics, species competition and water level.3.) Isoetes sinensis grows mainly in acidic softwater oligotrophic environments with considerably low level of dissolved carbon dioxide (DCD) and the pH in the water is controlled by the weak buffer system of CO2/HCO3-/CO32- and these environments have typically low conductance with very low alkalinity, hardness, nitrate, phosphate and total nitrogen and total phosphorous levels in the water layer.4.) Isoetes sinensis possesses crassulacean acid metabolism (CAM)-like photosynthetic pathway occurs commonly in submerged leaves in genus Isoetes and the magnitude of fluctuations is influnted by the water level and sunlight.5.) Isoetes sinensis has evolved a highly specific growth strategy and was unable to adapt to the changes in water physical and chemistry wrought by processes such as water alkalinizing, hardening, eutrophication and pollution by human activity and these factors probably result in the loss of Isoetes sinensis populations in some locations in Mainland China. The current populations of Isoetes sinensis are faced with the intense competition of other hydrophytes because of the loss and destroy of their habitat.Both in-situ and ex-situ conservation strategies are recommended for Isoetes sinensis based on the findings of this study. The aquatic or wetland habitats presently occupied by the natural populations of Isoetes sinensis should be set apart as priority areas for in-situ conservation and measures should be taken urgently for reducing or halting these detrimental processes to prevent decimation at the sites where there...