Ecological stoichiometry of nitrogen and phosphorus in Moso bamboo (Phyllostachys edulis) during the explosive growth period of new emergent shoots.

The ecological stoichiometry of Moso bamboo (Phyllostachys edulis) during the "explosive growth period" (EGP) remains unknown. In a previous study, we showed that the carbon (C) required by shoots during the EGP is derived from attached mature bamboos. In this study, we attempted to answer the following two questions: (1) Is the nitrogen (N) and phosphorus (P) required by shoots during the EGP also derived from attached mature bamboos? (2) Is the ecological stoichiometry of Moso bamboo during the EGP consistent with the growth rate hypothesis (GRH)? We simultaneously investigated changes in the N and P concentrations and N:P ratios of shoots (young bamboos) and attached mature bamboo over an 11-month period. During the EGP of Moso bamboo shoots (April 15-May 29), N and P concentrations in the shoots declined markedly because of the dilution of biomass and the transport to the germinated leaves and branches, and the N:P ratio remained at a low level. The significant correlations between relative height and biomass growth rates and the concentrations of N and P and N:P ratios during the EGP were consistent with the GRH. To meet the needs of "explosive growth," N was presumed to be transferred from the branches and rhizomes of attached mature bamboos to the shoots via underground rhizomes, while P likely came from mature bamboo leaves and branches. After the emergence of the branches and leaves of young bamboo: (1) the N concentration of the new leaves initially decreased and then increased, (2) P concentration exhibited a marked decrease, (3) and N:P ratio gradually increased. Our findings regarding the N:P ratio of shoots (young bamboos) during the EGP are consistent with the GRH, and we surmise that mature bamboo supplies N and P to attached young shoots via underground rhizomes.