Interaction of fire-related cues in seed germination of the potentially invasive species Paulownia tomentosa Steud

Abstract

The Empress tree (Paulownia tomentosa Steud.) is a fast growing deciduous tree originating from East Asia. It is grown as an ornamental plant, but can also be used as industrial wood. However, in some parts of North America, this species is considered invasive, with high impact on autochthonous populations. We have investigated whether post-fire expansion of this species can be explained at the germination level by analyzing the interaction between physical (light and temperature) and chemical (smoke and nitrogenous compounds) fire-related cues in the regulation of P. tomentosa germination. Light is the key environmental signal in the induction of germination of positively photoblastic P. tomentosa seeds. Smoke, applied in the form of extract (liquid smoke [LS]), stimulates light-induced germination if applied during imbibition, or shortly after the inductive irradiation. This stimulatory effect of LS can be effectively prevented by far-red light, suggesting that the mechanism of smoke action is phytochrome related. The LS had no effect on the germination percentage when applied during the phase of radicle protrusion. However, LS reduced radicle elongation and slowed its protrusion. The LS had no effect on the optimal temperature range of germination (23-27 degrees C). The combined action of LS and KNO(3) in light-induced germination was more effective then when each chemical was applied separately. It can be concluded that all tested components of fire, except elevated temperature, operate to stimulate germination of P. tomentosa seeds, suggesting that the post-fire invasive potential of this species can, at least in part, be explained at the germination level.