Growth response of hybrid aspen (Populus × wettsteinii) and Populus trichocarpa to different pH levels and nutrient availabilities

Populus plantations are mainly established on agricultural land, but natural forests soils typically have lower pHs and nutrient contents. In this study, growth responses of two commonly used Populus genotypes, hybrid aspen (Populus x wettsteinii Hamet-Ahti) and black cottonwood (Populus trichocarpa Torr. & A. Gray ex Hook.), were monitored in the greenhouse in relation of changes in pH and fertilizer levels in quartz sand and forest moraine soil. In quartz sand, changes in pH had no impact on growth or mortality of the two species. In forest soils, the lowest pH values, i.e., 3.5 and 4.0, caused plant mortality for P. trichocarpa but not for P. x wettsteinii. Growth optimum of P. trichocarpa occurred at a pH range of 5.5-6.5, whereas P. x wettsteinii showed a broader growth optimum at a pH range of 4.0-7.0. Fertilization expanded the pH range of optimum growth for P. trichocarpa but not for P. x wettsteinii. In both species, foliar content of nitrogen and potassium content increased after fertilization, whereas the foliar content of phosphorus was similar to unfertilized plants. Our results suggest that differences in tolerance to low pH values between P. x wettsteinii and P. trichocarpa might be connected to tolerance against aluminum. These findings may improve future establishment methods and identification of poplar genotypes suitable for forest land.