Clonal Growth Characteristics And Population Structure Of Nitraria Tansutorum

Nitraria tangutorum is in the family Zygophyllaceae and belongs to the genus Nitraria L. It is endemic to China and distributed mainly over Xinjiang, Tibet, Ningxia, as well as Mongolia provinces. N. tangutorum grows mostly under harsh environment, such as arid and semi-rid regions, and it is the constructive specie in those regions. N. tangutorum can effectively prevents windstorms and fastens sand and plays an important role in keeping the ecological balance in of China. It has the characters of heat-resistantance, saline-alkali tolerance, and endurable to drought and barren resistance.Due to the failure of seed-originated seedlings, the regeneration of N.tangutorum mainly depends on the clonal propagation of steem-layering under natural conditions. Althoug a great deal of research has been conducted about N. tangutorum, its clonal growth characteristics and population structure has not been studied at present. However, N. tangutorum shrubs are undergoing severe degradation in recent years as a result of water shortage, sandstorms, and human disturbance.By studying sand burial depth of sprouting buds, germinaiton rate of axillary buds, formation point number of adventitious root, as well as biomass allocation of modules for ramets, we analysed the characterstics of clonal growth about N. tangutorum on fixed and semi-fixed sandy land, and examined the influence of the length and diameter of layering on it. Based on the theory of life Tab.le and survival analysis, the age structure and life Tab.le of N. tangutorum were analyzed at genet and ramet levels by plot investigation and data analysis. The investigation indicates that,(1) The clonal ramet was formated on the branches which were buried by sand, and those branches are named as layerings. N. tangutorum exhibited sympodia branching pattern and guerilla architecture, and it has strong ability to spread. There were significant differences between the length and branching rate of layerings for N. tangutorum populations on the two types of sandy land, while the braching angle of layering were similar to each other. Genet polution on fixed sandy land were higher that semi-fixed, and the amout of ramet and layering were also more than latter one. There were longer layerings and more ramets for the population on fixed sandy land compared with semi-fixed one. And the sand burial depth of sprouting buds of N. tangutorum populition on fixed sandy land was significantly lower than that on semi-fixed sandy land.(2) The number and germinaiton rate of ramet were significantly associated with the layering length, and they were extremely significantly associated with the diameter of layering. There was extremely positive correlation between the formation point number of adventitious root and the length of layering. The amount of ramet clonal ramet number was significantly related to the layering diameter. The number of ramet, dead ramets rate, as well as the biomass allocation of root were decreased with the increasing of layering class, while more biomass was allocated in the above-ground part of ramet.(3) The spacer length was shorter growing on fixed sandy land than that on the semi-fixed. There was more clonal growth in the first population, and the branching rate of layering was higher in this populition. Its rate of dead ramets was also higher compared with the population growing on semi-fixed sandy land.(4) The percentage of population individual numbers at genet and ramet levels both increased first, but then decreased with age class increasing. The survival curve of the two populations trended to the type of Deevy-I. Moreover, the fluctuation of mortality rate and risk rate were obvious during natural regeneration progress on the two levels. And both of the populations had two mortality rate peaks. The risk rate of genet population was in the wave through at the3rd age class. In contrast, the risk rate of ramet population was on the peak at the same age class.