Foliar, root and rhizospheric soil C:N:P stoichiometries of overstory and understory species in subtropical plantations

Ecological stoichiometry provides important information for understanding biogeochemical cycling in forest ecosystems. The stoichiometric characteristics of carbon (C), nitrogen (N) and phosphorus (P) in the leaves, roots and rhizosphere soils of co-existing overstory trees and understory shrubs and herbs within a forest ecosystem, however, remain poorly understood. The C, N and P concentrations and their stoichiometric ratios of the leaves, roots and rhizosphere soils were studied for three overstory trees, three understory shrubs and two herbs in three plantations of Cunninghamia lanceolata, Pinus massoniana and Pinus elliottii in subtropical China. Mostly, the foliar and root C:N ratios were significantly higher for overstory trees than understory shrubs and herbs. Forest type significantly influenced the C:N and C:P ratios of the leaves and rhizosphere soils across all species. The C:N ratio in the leaves and roots were positively and negatively correlated with that in rhizosphere soil, respectively. The N:P in leaves and roots were negatively and positively correlated with that of rhizosphere soil, respectively. We found that foliar and root C:N:P stoichiometry varied greatly among plant species and forest types, which was mainly constrained by the rhizosphere soil. The opposite relationship of C:N:P stoichiometry in the leaves and roots with rhizosphere soil offers new insights into the interaction between above- and belowground process of forest ecosystems.