Abstract: Mixed forests of Phyllostachys edulis and Phyllostachys prominens are developing due to their mutual invasion in the adjacent distribution regions of these two bamboo species. To compare the plasticity and competition of Ph. edulis and Ph. prominens, a field experiment was conducted to explore the adaptive features of rhizome and roots of Ph. edulis and Ph. prominens in the pure and mixed forests. The results showed that rhizome diameter and node length, specific root length, densities of root length, surface area and volume, rhizome biomass, root biomass and total rhizome and root biomass of Ph. prominens were all lower than those of Ph. edulis, while an opposite pattern was found for the specific rhizome length, and densities of rhizome length and rhizome node. No differences in root diameter and fractal dimension between the two bamboos were found. Morphological character and biomass allocation for rhizomeroot system of Ph. edulis and Ph. Prominens changed after mutual invasion. Rhizome diameter of Ph. edulis and rhizome node length of the two bamboos increased, but densities of rhizome length and node of the two bamboos, specific rhizome length of Ph. edulis all decreased remarkably. Density of root length, surface area and volume, biomass of rhizome, root and total rhizome and root biomass of Ph. edulis and Ph. Prominens all decreased greatly, while specific root length and allocation proportion of rhizome for the two bamboos increased obviously. The relative yield for the two bamboos was significantly less than 1, and competitive balance index (Ph. prominens/Ph. edulis) was less than 0. Furthermore, the competitive balance index of rhizome and root was significantly higher than that of rhizome. All those results indicated that rhizomeroot system of Ph. edulis was more plastic than that of Ph. prominens. There was intense interspecific competition among the two bamboos in the mixed forest, and Ph. edulis was more competitive than Ph. prominens, and rhizome root system played a leading role in competition between Ph. edulis and Ph. prominens.

Key words: leaf stoichiometry, Quercus acutissima., provenance, variation