Studies On The Biodiversity Of Aquatic Plants In The Arid Zone Of Northwest China

The arid zone in the Northwest China including Xinjiang, Hexi corridor in Gansu province, Qaidam basin in Qinghai province, Alxa Plateau in Inner Mongolia Autonomous Region and western Ningxia, is located in the centre of Euroasia mainland. It covers an area of 241.5×10~4km~2,1/4 of total area of China. Although a fairly good account of the past floristic history of arid zone is available, the knowledge of the flora of aquatic vascular plants remains woefully inadequate. During the period of 1998-2004, field expeditions and floristic collections of aquatic vascular plants were carried out throughout the arid zone. The main results are as follows:1. The results obtained from the present field study during four years and literature survey showed that a total of 226 species belonging to 65 genera and 35 families. Among these, 6 species, 5 genera and 5 families belong to Pteridophyte, 141 species, 32 genera and 15 families belong to Monocotyledon, and 79 species, 28 genera and 15 families belong to Dicotyledon.2. Among those, 1 genus (Sublaria) and 2species (Sublaria aquatica, Batrachium nipponicus) were new state records and 2 families (Azollaceae and Pontederiaceae), 9 genera and 29 species were new area records.3. The flora of aquatic vascular plants in the arid zone was basically temperate in nature. Among 226 species or subspecies representing 65 genera and 35 families, 22.3% species, 50 % genus and 73.5 % families were cosmopolitan, and 60.3 % species, 31.3 % genus and 17.7 % families were temperate.4. Aquatic plant diversity was distributed unevenly in the zone, analysis of the total numbers of aquatic plant species in the five sub - regions did not show a significant linear relationship between area and total aquatic plant species. The maximum species occurs in Dzungarian basin and the least species in Hexi corridor. Beta diversity was measured here using Wilson - Shmida index (Bt) to represent species compositional turnover between sub -regions, the peak in beta diversity was that between Tarim basin and Qaidam basin and between Dzungarin basin and Qaidam basin. This may reflect the large extent of biotic change and also reflect rapid and ecologically significant change in these sub - regions. This may be explained by altitude significant change, the average altitude of Qaidam basin is 2600 - 3000 m, but the average altitude of Tarim basin and Dzungarin basin is 1000m and 600m respectively.5. the result of clustering analysis in the present study indicated aquatic plant flora in the arid zone could be divided into three phytogeography sub- regions, which were Tarim basin and Dzungarin basin phytogeography sub - region, Hexi corridor and Alxa Plateau phytogeography sub - region, and Qaidam basin phytogeography sub -region.6. Comparison of the results with flora of aquatic plants of other arid zone (Australia) reflected the composition of the aquatic flora of the arid zone in China at family level was not grossly different from that of Australia, but at genera and species level especially at species level aquatic plants represented in the zone differed significantly from that of Australia.7. A preliminary study of latitudinal gradient patterns of aquatic vascular plant the mid-latitudinal zone hosted the largest number of family, genus and species. The proportion of tropical genera decreased with increasing latitude, and the proportion of temperate genera increased with increasing latitude. The same pattern existed with longitudinal gradient. But the trend of change in the proportion of three main categories (cosmopolitan, tropical and temperate) with longitudinal gradient was notapparent.8. A unimodal relationship between aquatic species richness and elevation was observed, with maximum species richness at 1000-15000m. The proportion of tropical genera decreased with increasing elevation, and continuously decreased to 0% at the elevation over 2500m. The proportion of temperate genera increased with increasing elevation at lower elevation zone, but decreased with increasing elevation at higher elevation zone. The proportion of cosmopolitan genera increasing with increasing elevation as a whole.9. For the species (Ranunculus natans) examined in this study, significant morphological differences existed within and between populations. Each of these morphological CV (coefficient of variation) was different within and between populations. Each of ecological factors resulted in different patterns of phenotypic variation. Among these ecological factors, the water availability was the most main for leaf morphological differences. A strong correlation occurred between altitude and leaf area and perimeter, and between longitude and dissection index.10. Analyses of 3 years field data showed that significant and positive relations existed between a - diversity of species and a - diversity of genus and family in both entire arid zone and five sub - zones. In contrast, 8 - diversity at species level was difficult to predict from 8 - diversity indexes at higher taxonomic level. The results indicated that higher- taxon a - diversity, especially at the generic level in our research, could be considered useful index in the studies of species spatial patterns for aquatic plant conservation in China, although their 8 - diversity indexes were comparatively poor predictors. So we believed that family- and genus-level field surveys represent a very promising approach to determine priorities area for conservation of aquatic plants.