Recent theories indicate that N is more in demand for plant growth than P; therefore, N concentration and N : C and N : P ratios are predicted to be positively correlated with relative growth rate (RGR) in plants under nutrient-enriched conditions. This prediction was tested in this study.

Chengdu Institute of Biology, Chinese Academy of Sciences Prof.SUN Shucun' s team examined the whole-plant concentrations of C, N and P and RGR, as well as the relationship between RGR and the concentrations and the ratios of N : C, P : C and N : P, for different harvest stages (the days after seed germination) of the seedlings of seven shrub species and four herbaceous species grown in N and P non-limiting conditions.

Meanwhile, the relationships among plant size, nutrient concentrations and ratios were subsequently determined.  In this study, researchers found that RGR was positively correlated with N concentration and the ratios of N : P and N : C when the data were pooled for all species and for each shrub species, but not for individual herbaceous species.

However, the relationship between RGR and P concentration and P: C was not significantly correlated for either shrubs or herbs. The variation of N among harvest stages and species was much greater than that of P, and the variation in N : P ratio was determined primarily by changes in N concentration. The shrub species differed from the herbaceous species in their N and P concentrations, nutrient ratios and in intra-specific relationships between RGR and nutrient ratios.

These differences possibly reflect differences in the capacity for P storage and biomass allocation patterns. In general, CIB researchers' data support recent theoretical predictions regarding the relationship between RGR and C : N : P stoichiometry, but they also show that species with different life forms differ in the relationships among RGR and C : N : P stoichimetries.

This study has been supported by Chinese Academy of Sciences, Chinese Ministry of Science and Technology and ECORES Lab. More results have been published in JOURNAL OF PLANT ECOLOGY-UK .