| Leymus chinensis and Agropyron michnoi are typical clonal plants of perennial herbaceous rhizome of Gramineae. They distribute widely,are salt-tolerant and have high nutritive value and better palatability to feed animals. They are important germplasm resources in China. Both quantity dynamics and the structures of the two perennial herbages with different densities and proportions were researched in this dissertation. The effects of intraspecies relationship and interspecies relationship on vegetative propagation of L.chinensis and A. michnoi experimental populations were analyzed to reveal convergent adaptation and succession regulation, and to enrich plant population module and community succession theories. The results showed:After two seasons, growth, the densities of L.chinensis and A. michnoi populations increased 16.5-47.1 times and 44.5-94.8 times in initiative density 36 tillers/m2 plots, and increased 48.0-129.3 times and 127.0-173.3 times in initiative density 16 tillers/m2 plots. This showed that L.chinensis and A. michnoi both occupied niche space quickly by vegetative propagation, and the speed of vegetative propagation of A. michnoi was quicker than that of L.chinensis in relatively favorable and fertile environment.After two seasons, growth, the tillers of L.chinensis consisted of three age classes and had an expanding age structure in every plot, and A. michnoi consisted of four age classes, some had a stable age structure in higher proportional experimental plots, others had an expanding age structure. The rhizome of L.chinensis and A. michnoi both consisted of two age classes. Total length of rhizome of L.chinensis population and most of A. michnoi population had a stable age structure in experimental plots.The tiller biomass of L.chinensis population all had an expanding age structure in different initiative densities experimental plots. The tiller biomass of A. michnoi population had an expanding age structure in 36 tillers/m2 plots,but others had a stable age structure in 1:0,1:5,3:1 plots of 16 tillers/m2. Rhizome biomass of L.chinensis population and A. michnoi population per area had a stable age structure except 1:1 plot of 16 tillers/m2 in A. michnoi population.Rhizome length is important measure of niche space expanding ability for clonal plant. After two growth, seasons, the total rhizome length were 11807.9±6444.6cm/m2 in L.chinensis population and 13529.0±8987.6cm/m2, and 4722.3±2633.9cm/m2 and 5137.1±2805.8cm/m2 in A. michnoi population with initiative densities of 36 tillers/m2 and 16 tillers/m2 plot. The length of rhizome in L. chinensis populations were about 2.5 and 2.9 times bigger than that in A. michnoi populations, respectively. It indicated the space expanding ability of L.chinensis was much stronger than that of A. michnoi. In two growth seasons, the number of leaves of L. chinensis and A. michnoi increased with the increase of the tiller height,and their leaf biomass both increased with the increase of the height and the tiller biomass,but the allocation of leaf biomass both decreased with the increase of the height and the tiller biomass in single and mixed populations. The generation rate and biomass accumulation rate of leaf with the growth of tiller in L. chinensis population were both higher than in A. michnoi population, but the depressed rate of allocation of leaf biomass with the leaf biomass accumulation was lower than in A. michnoi population. Compared with A. michnoi, L. chinensis showed some growing dominance, the same as single population while compared with mixed population.The number of tillers, tiller biomass and rhizome length of L. chinensis population decreased with the increase of the number of tillers, tiller biomass and rhizome length of A. michnoi population in exponential function. The number of tiller node buds of L. chinensis decreased with the increase of that of A. michnoi population in linear function. The depressed trend of the number of potential population and rhizome biomass were not obvious.There was different ability of space expanding in different A.michnoi clones, but the number of tillers increased with the increase of space expanding area, the rhizome length and the number of every potential population in different clones increased with the increase of space expanding area and the number of tillers. The development of the number of tillers, the rhizome length, the number of total potential population and dormancy seedlings followed the same regulation, and the development of the number of total buds and rhizome buds followed the same regulation. The aboveground and underground parts of the clone expanded niche space at the same time.According to the trend of present development of the two populations, the dominant position of L. chinensis population will show up gradually and A. michnoi will become the companion species in mixed community with the community succession.
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