Response of trembling and hybrid aspens to phosphorus and sulfur fertilization in a Gray Luvisol: growth and nutrient uptake

A greenhouse experiment was conducted to investigate the effects of P and S fertilization on the growth and nutrition of two aspens, a clonal aspen (Populus tremuloides Michx.) and a hybrid aspen (a mixture of Populus tremu loides × P. tremula L. and Populus tremula × P. tremuloides), grown in a Gray Luvisol fertilized with N. Phosphorus application significantly increased basal diameter (BD) increment and most other growth parameters for both clonal and hybrid aspens, whereas S application increased BD increment only for the hybrid aspen. Diameter increment, leaf area, and seedling biomass were generally increased by P application, regardless of S levels, but they responded to S application only if P was also applied. Phosphorus application significantly increased foliar P concentrations and foliar N and P contents and their uptake for the clonal aspen. For the hybrid aspen, P application increased foliar N, P, and S concentrations, contents, and uptake. Sulfur application significantly increased foliar S concentration, content, and uptake for the hybrid aspen but not foliar N concentration, content, and uptake for the clonal aspen. Except for height increment, growth parameters were significantly related to foliar percent P and N/P ratios and percent S and N/S ratios. It can be concluded that both P and S were deficient, but P was more limiting after potential N limitation was removed.