Size-dependent C, N and P stoichiometry of three submersed macrophytes along water depth gradients

Variability in biomass allocation and growth rate of submersed macrophytes along water depth gradients may lead to different carbon (C), nitrogen (N) and phosphorus (P) stoichiometric characteristics. We conducted a field investigation to evaluate long-term effects of water depth on C, N and P stoichiometry of three submersed macrophytes, Potamogeton maackianus, Myriophyllum spicatum and Ceratophyllum demersum. The results indicated that shoot C:N, C:P and N:P of the plants tended to increase with elevated water depths, and patterns of biomass allocation along water depth gradients were more important than biological dilution of increased growth rates in affecting shoot C:N:P stoichiometric characteristics of the plants. Partial correlation analysis using shoot height and biomass as covariates revealed that water depth significantly affected C:P ratios in shoots of P. maackianus and M. spicatum and C:N ratio in shoots of M. spicatum, but did not affect N:P ratios of all the plants. Shoot stoichiometry of M. spicatum was most sensitive in response to water depth, followed by P. maackianus, and that of C. demersum was really unchanged with elevated water depths. Our results suggested that strategies in biomass allocation in organs, which depend largely on the species identity, rather than growth rates of the plants, contributed mainly to variation in the observed element stoichiometry along the water depth gradients.