The Adaptability Of Caragana Tibetica On Ordos Plateau, China

Arid and semiarid ecosystems are very important ecosystem types. They cover one third of land area in the world, produce more than 35% of global land net primary production and possess an excess of 30% of global organic carbon reserves. However, these ecosystems are more vulnerable and susceptible to degradation under climate changes and human activities. Water is a limited factor in these regions, and plays a crucial role in terms of plant survival and production, the structure and productivity of ecosystem and dynamics of vegetation. Ordos plateau is a relatively independent natural unit in arid and semiarid areas of China, and also a highly unique and susceptible ecotone. Caragana tibetica community is an important community type in the ecotones between steppe and desert of this region, and acts as a crucial pasture. In this study, we analyzed characteristics of C. tibetica in terms of community, population and biology, and also analyzed the effects of the nebkhas it induced to explore its adaptive characters to the arid environment. Our results were shown as follows:1. Caragana tibetica community belonged to the vegetation type of steppe desert. (1) Caragana tibetica community covered an area of about 3684 km2, and could be separated into 15 association. (2) The coverage of C. tibetica was about 11% and there were about 42 C. tibetica individuals per unit 100 m2; the Simpson and Shannon-Wiener diversity indices of herbs were both about 7.3. (3) There were 88 seed plant species in the C. tibetica community, which belonged to 26 family and 58 genera. Among these plants, family Gramineae contained the largest number of genus and species, and then followed by the family Compositae. The genus Artemisia had the largest number of species and the genus Stipa took the second place. In addition, there were 7 strong xeric species and 52 typical xeric species in C. tibetica community.2. Caragana tibetica community showed a stable structure. (1) The vertical structure was shown that:for the aboveground parts of the community, the height of dominant synusia was about 25 cm, and that of sub-dominant synusia consisting of bunchgrasses Cleistogenes songorica and Stipa breviflora ranged from 5 to 10 cm; for the belowground parts of the community, C. tibetica had bimodal root activity profile and most roots concentrated in the 0-200 cm soil layers with a certain amount of adventitious roots growing. The small roots and fine roots separately concentrated in 20-60 cm and 140-170 cm soil layers. The root system of herbs mainly distributed in 0-30 cm soil layer. (2) The horizontal structure was shown that:at the spatial scale of 10 m×10 m, C. tibetica individuals showed random pattern, while Caragana stenophylla, Convolvulus ammannii and Ptilotrichum canescens showed aggregation patterns. With the spatial scales increasing, Stipa breviflora, Cleistogenes songorica, Astragalus efoliolatus and Artemisia frigida firstly showed aggregation patterns and then exhibited random patterns. (3) Caragana tibetica did not show associations with other perennial species, and no interspecies competition was found among them. (4) Caragana tibetica caused the spatial heterogenous distributions of soil total nitrogen, soil organic carbon and soil moisture, which however did not influence the distribution patterns of other perennial species in the community. Therefore, soil nutrients accumulated by C. tibetica could not be used by other perennial plants.3. The distribution patterns of C. tibetica populations varied with the decrease of the precipitation. With the precipitation decreasing, the uniform distribution patterns of both the live and mature C. tibetica individuals at a certain scale were replaced by the random patterns.4. Morphologically, C. tibetica showed dwarf and near hemi-oval shape, and its average canopy was 57 cm in length and 44 cm in width. Both the root and stem of C. tibetica had the ability of split.5. Caragana tibetica nebkhas showed the sand-fixing and fertile island effects. (1) In C. tibetica community, the amount of sand trapped by C. tibetica per unit area was 0.0313 m3m-2. Caragana tibetica primarily accumulated fine sand, which accounted for 74% of the soil in the nebkhas. (2) The contents of soil organic matter and total phosphorus and soil moisture inside nebkhas were higher than those outside the nebkhhas. Inside the nebkhas, contents of soil organic matter and total phosphorus first increased and then decreased with increasing soil depth with the maximum value occurring in the layer of 20 cm, but soil moisture increased steadily.In a word, C. tibetica showed strong abilities to adapt arid environment, and the formation of nebkhas facilitated its growth and development. Yet, despite of the stability of C. tibetica community, more attentions should be paid on its rational utilization in view of current serious destruction and significant ecological functions of the species. In summer and autumn its community could be used as pasture while in winter and spring the protective measures should be considered to take. Our study provided more systematical understandings of the relationship between arid environment and plant, which will have profound significance for ecological restoration and sustainable utilization of resources.