Correlations between leaf, stem and root functional traits of common tree species in an evergreen broad-leaved forest

In this paper we try to explain the relationships between the functional traits of different plant organs based on three hypotheses, i.e., the structural similarity hypothesis, functional similarity hypothesis and above and below-ground coordination hypothesis. We selected sixteen main tree species in the evergreen broad-leaved forest in Dagangshan, Jiangxi Province. Fifteen functional traits of these species were measured, including specific leaf area, specific root length, tissue density, carbon content etc., which could be classified into structural trait and chemical trait categories. Multiple t test and Pearson correlation test were used to analyze the correlations between functional traits of root, stem and leaf. For structural traits, there was no significant correlations between specific leaf area and specific root length. Tissue density differed significantly among the three organs and the correlation between stem and root tissue density was stronger than that between other organs. For chemical traits, the carbon contents showed little difference among the three organs and their pairwise correlations were extremely strong. The nitrogen content was higher in leaf, medium in twig and lower in fine root, and the correlations between leaf and root nitrogen contents were significant. Besides, twig phosphorous content was the highest, and the phosphorus contents of the three organs were positively related. Our results on the relationships of structural traits support the structural similarity hypothesis while the relationships of the nitrogen content support the functional similarity hypothesis. Meanwhile, the above and below-ground coordination hypothesis is supported by our results on carbon and phosphorous content. In conclusion, the functional traits of leaf, stem and root are coupled and may reflect the ecological strategies of plants to adapt to the environment.