Reproductive Ecological Characters And Mechanism Of Population Competition Of Agropyron Michnoi

Hulunbeier sandy land has been a degenerate grassland type due to the unreasonably use of mankind. The desertification situation had negatively impacted the environment in the north of China and hampered the development of local economies. Therefore, it is crucial to restore the vegatation of Hulunbeier sandy land. Agropyron michnoi (short for A.michnoi), a species of typical clonal plant, is very adaptive to the sandy environment. In order to enrich and extend the theories of population reproductive ecology, at the angle of population reproduction physiology, we studied the reproductive characters at different growth areas in sandy land and at the condition of competition with Lymus chinensis(short for L.chinensis), to reveal the mechanism of reproductive extention and adaptability. A brief account of the research is as follows:Studies on the breeding characters of A.michnoi in different stages of vegetation restoration shown that:(1) Tiller, rhizome and seedling components of A.michnoi were in the expansive structure on the shifting sandy land, which became the dominant population in community depending on the rapid growth of clonal components. When recovery of plant was on the stage of fixed sandy land, the components of which were all in stable age structure. That means, under certain environment carrying capacity, the community was the stable type and still keeps in dominant population without disturbance.(2) It reproduced the smaller ind ividuals which were larger in number A. michnoi mainly depends on vegetative reproduction. With the natural recovery of desertification grassland, population constitute of A.michnoi changes from the bigger individuals which were smaller in number to the smaller individuals which were larger in number and at the same time.decreased the ratio of sexual reproduction, which means, it has completed the changing process from R-strategy to K-strategy. (3) Why the A.michnoi becomes the pioneer species in sandy land because the 25% of seeds of A.michnoi could sprouted the individuals. But the ratio of offspring derieved from their sexual reproduction accounted for less than 6% of real population and gets well below the offspring derieved from their vegetation reproduction. Yet, On the fixed sandy land, A.michnoi cannot be established by seed and its populatuon totally depended on the vegetative reproduction.(4) In vegetatively potential population of A.michnoi, the ratio of the juvenile seeding was obviously higher than of the dormancy bud did. The ratio of the growth of the tillering-node seedling into the real population was higher than that of the rhizome seedling. With the improvement of sandy land habitats, the growth efficiency of the juvenile tillering-node seedling and juvenile rhizome seedling on the fixed sandy land was apparently higher than that on the shifting sandy land.The study of the reproductive strategies of intra-specific competition between A.michnoi and L.chinensis at the transitional process from sandy land to grass land has shown:(5) With the increase of growing years, In total biomass of population, A.michnoi was declining while L.chinensis maintained the increasing momentum.The chief reasons was L.chinensis adopted the strategy of quicly-occupied the underground niche in the interspecific competition, which made the rhizomes biomass of A.michnoi less and reduced its ability to get the energy from underground resources. So A.michnoi was in status of inferior position in the interspecific competition. (6) In 3 years, the regularity of age structure for the number of A.michnoi s tillers changed from growth form to tend to be stable form, then to decline form. While that of L.chinensis all showed growth form apparently. Which means A.michnoi may lose its dominant position and L.michnoi would take the advantage position of A.michnoi in the interspecific competition.