Abstract: Leymus chinensis (Trin.) Tzvel. is a rhizome grass species with high vegetative propagativity. A single species dominancy community of L. chinensis is often developed by vegetative propagation in suitable habitat. The species has two divergence types, a grey-green and a yellowgreen, in the Songnen Plain of China. The age structures of the tillers and rhizomes of the two types of clonal populations in the single species dominancy communities of L. chinensis in natural grassland were comparatively analysed. The standards of age differentiation were that the tillers developed from rhizome buds were age one, while the ages of others were identified with the generation numbers of vegetative propagations of the tiller nodes. Rhizomes of age one were developed in the current growing season, and the ages of others were defined as the number of their surviving years. The ages of each tiller or rhizome were respectively distinguished by morphological characteristics including positions of the tiller nodes and the marks of surviving tillers of vegetative daughters. The results showed that the tiller node lived 2 to 4 years in general, the oldest could live up to 5 years, and the rhizome lived 2 to 3 years in general, occasionally up to 4 years. The age spectrum of tillers from age one to age four in the grey-green population was 65.5 %, 26.6 %, 6.6 % and 1.3 % respectively, and likewise that in the yellow-green population was 63.2 %, 27.8 %, 6.9 % and 2.1% respectively. For the clonal populations of the two types, the tillers showed expanding age structures, and the tillers of age one had largest productivities, while those of the age three had evidently decreased. The accumulative length of the rhizomes of the yellow-green population was 21 218 cm/m2, and that of the grey-green populations was 18 035 cm/m2. The biomass of rhizomes demonstrated a linear decrease in relation to age increase. The vegetative propagativity of age one rhizomes was the largest, the number of buds being far more than the total above-ground tillers at the mid-ten days of August. The age two rhizomes had less potentiality of vegetative propagation and those of age three and age four had lost all the vegetative propagativity. The clonal populations of the two types of L. chinensis were always recruited through the rhizome budding.

Key words: Leymus chinensis, Divergence type, Tiller, Rhizome, Vegetative propagation, Age structure, Clonal population