Consistent responses of the C:N:P stoichiometry of green leaves and fine roots to N addition in poplar plantations in eastern coastal China

Aims Ecological stoichiometry plays an important role in biogeochemical cycles and ecosystem functions. However, we know little of fine-root stoichiometry responses to nitrogen (N) addition and whether the responses are similar to those of leaves. Methods We conducted a field experiment to explore the effects of N addition on carbon: N: phosphorus (C:N:P) stoichiometric ratios and homeostasis in green leaves, fine roots and soil as well as the regulatory effects of plant and soil stoichiometric ratios on forest growth in poplar plantations on the eastern Chinese coast. Results We found that N addition increased soil organic C (SOC), soil available N and P, and soil N:P and decreased soil C:N. We also found that N addition increased leaf C and N, N:P and C:P of green leaves and fine roots, while it decreased fine root C and P as well as green leaf and fine root C:N. The consistent responses of green leaf and fine root stoichiometry to N addition were attributed to stoichiometric homeostasis. That diameter at breast height (DBH) and fine root biomass (FRB) growth contradicted C:N:P stoichiometry appeared to be because of their different nutrient uptake and utilization efficiencies. Conclusions The C:N:P stoichiometry of green leaves and fine roots was generally consistent in response to N addition. These findings contribute to our understanding of the biogeochemical cycles of plantation ecosystems and provide basic data for plantation cultivation and management.