Shoot growth dynamics and the mode of competition of two rhizomatousPolygonum species in the alpine meadow of Mt. Fuji

The growth dynamics of shoot populations and the mode of competition between intra-clonal shoots of two rhizomatous species,Polygonum cuspidatum andPolygonum weyrichii, were investigated at the Houei crater (c. 2380 m a.s.l.) of Mt. Fuji. Three genetic individuals ofP. cuspidatum (large, medium and small) and five genetic individuals ofP. weyrichii were selected for this research. The growth dynamics of shoot populations were analysed using the diffusion model. InP. cuspidatum, linearG(t,x) functions (mean of absolute growth rates of shoots of sizex at timet in the diffusion model) with positive slopes were found in terms of shoot weight in three genetic individuals. The linearG(t,x) functions suggest that smaller-sized shoots were supported by means of physiological integration and not suppressed by larger-sized shoots. As in other clonal plant species, size-independentD(t,x) functions (variance of absolute growth rates of shoots of sizex at timet in the diffusion model) were found inP. cuspidatum. A similar tendency was also found in the five genetic individuals ofP. weyrichii. There was large variance of RGR in terms of shoot weight irrespective of values ofC _r(t,x), defined as (total leaf area of shoots larger thanx at timet/total leaf area of all shoots), in both thePolygonum species. This means that there was a higher probability of growth for smaller shoots, suggesting that competition between shoots was symmetric (two-sided) in bothP. cuspidatum andP. weyrichii.