Biomass Allocation and Resprouting Ability of Princess Tree (Paulownia tomentosa: Scrophulariaceae) Across a Light Gradient

Abstract

Acclimation to low light may interfere with the ability of woody plants to resprout. We examined the patterns of biomass allocation and resprout ability of seedlings of Paulownia tomentosa, a heliophytic r-selected species. Plants were grown in shade houses in a common garden with two replicates of three light treatments: full ambient light, artificial edge and shade. The shade treatments were similar to light patterns and levels typical of a deciduous forest understory. The artificial edge treatment provided an intermediate light regime since it received only direct morning sun and was shaded in the afternoon. The experimentally browsed treatment consisted of clipping 10 tree seedlings to ground level in each replicate light treatment four times over the growing season. In all light treatments, whole plants were harvested on each clipping date. Plants in all treatments allocated more to belowground biomass in the first weeks of the experiment and then shifted allocation to aboveground biomass. Plants grown in shade had lower relative growth rates (RGR) and higher specific leaf areas (SLA) and leaf area ratios than plants in the other light treatments. Ability to resprout was influenced by the amount of accumulated belowground biomass and, since this was lowest in the shade treatment, resprouting was reduced in low light. Increased SLA was not correlated with an increase in RGR. Also, correlation networks showed decreased integration in the shade. Our data suggest that, although resprout ability is dependent upon belowground biomass, P. tomentosa seedlings can resprout at an early age, even in low light. This ability may allow the species to become established even in areas of high herbivore density.