Nitrate stimulates root suckering in trembling aspen (Populus tremuloides)

In a greenhouse experiment, we tested whether the initiation, density, and growth of trembling aspen ( Populus tremuloides Michx.) root suckers are related to postdisturbance soil nutrient availability. After decapitation of functional 2-year-old aspen root systems, nutrient solutions adjusted for various concentrations and forms of mineral N, different concentrations of Ca2+, K+, or PO43–, and different pH were applied to the roots and their suckering response was assessed after 35 days. Root systems treated with NO3– at concentrations of 1.5 and 7.5 mmol/L produced nearly double the sucker density compared with an unfertilized control, while fertilizing with N in the form of NH4+ did not affect sucker numbers, regardless of concentrations. The best growth of suckers was achieved with a mixture of 15 mmol/L NO3– + NH4+whereas the lowest growth was observed with 15 mmol/L NH4+. Neither Ca2+, K+, and PO43– nor the pH tested in this study impacted sucker density or growth. This has implications for understanding the impacts of disturbance on forest succession and the subsequent regeneration of aspen stands. The results suggest that the amount of nitrification, depending on the type and severity of disturbances, will influence the regeneration density of aspen.