Complex dynamics of twig elements and stoichiometric ratios with altitude changes in the typical dry valley, eastern Qinghai-Tibet plateau

Abstract

The concentrations of carbon (C), nitrogen (N), phosphorus (P) and stoichiometric ratios of twig (i.e. stem and leaves) are the important indicators to connect plant individual and the abiotic environment, which reflects the nutritional status for plants and ecosystem function. However, the variations of stoichiometric characteristics of twig C, N and P across altitude gradient have not yet been extensively studied. In the present study, we determined the elements (C, N and P) concentrations of current-year twigs from 1050 to 3070 m woody plants in the Bailongjiang River Basin (BRB), a typical dry valley of eastern Qinghai-Tibet plateau. And then, the relationships between altitude and the element concentrations of twigs, stems, and leaves had been explored by linear regression, allometric analysis and phylogenetic analysis. The results showed that: the frequency distribution of elemental concentrations and stoichiometric ratios was left-deviations. The C, N and P concentrations were 395.66 mg g−1, 17.59 mg g−1 and 1.53 mg g−1 for leaves, 414.83 mg g−1, 8.76 mg g−1 and 1.13 mg g−1 for stems, and 401.72 mg g−1, 8.78 mg g−1 and 1.51 mg g−1 for twigs, respectively. The stems elemental concentrations and stoichiometric ratios were positively correlated to that of the leaves. Except for the N of stem and twig, the other elemental concentrations were significantly correlated to altitude. And the leaves and stems N/P and C/P, and twig C/P were significantly negative correlated to altitude. The significant isometry relationships were observed between N vs P of leaves, stems and twigs. The elemental concentrations and stoichiometric ratios of BRB woody plant had no statistical phylogenetic signal. This study presented the evidence that the leaf, stem and twig C, N and P concentrations and stoichiometric ratios from wider altitude-gradient within BRB, it was special and varied largely in different elements, stoichiometric ratios and locations, which supported the growth rate theory in the whole.