Dynamics of age structures on Agropyron michnoi and Leymus chinensis in different communities

Agropyron michnoi (short for A. michnoi) and Leymus chinensis (short for L. chinensis) are both rhizome grass in clonal plants. A. michnoi is one of the pioneer species in the secondary succession process showing good adaptivity to the Hulunbeier sandy environment, While L. chinensis is a dominant species of zonal vegetation. The coexistance of A. michnoi and L. chinensis populations in the succession indicated that, the seral process has entered into the transition stage from sandy vegetation to normal grassland plant. To understand its details, the three sample plots were prepared in the mixed dominant population community, ie. A. michnoi solitary plot (P1), L. chinensis solitary plot (P2) and mixed plot (P3). The method of plant reproductive ecology was used in excavation sampling in the elemental area (25cmx25cm, depth 30cm), and it was repeated for 5 times. The mixed dominant population community was investigated and the age class of tillers was identified by the age structure of tillering nodes. The results indicated that ramet modules of A. michnoi consisted of 3 or 4 age classes respectively in 2009 and 2010, in single and mixed communities; While L. chinensis consisted of 2 age classes; As for A. michnoi, the variations of ramet modules numbers were similar to those of biomass age structures. The fact reveals that, with the increase of growing years, there may be a downward trend of low age class and an upward trend of high age class. As a result, the single community always the growth type, but may close to stable type, and the mixed community may chang from growth type to stable type. Additionally, the number of ramet modules and biomass age structures of L. chinensis all showed growth type apparently in 2 years running. The single plant productivity of L. chinensis of all age classes was 5.2 times higher than that of A. michnoi on average. The changes of the tiller's age structures showed the tendency that the superiority of A. michnoi community may be replaced by L. chinensis.