How do Size and Resource Availability Control Aboveground Biomass Allocation of Tree Seedlings?

In a three (light availability levels)×two (soil moisture levels) factorial greenhouse experiment we quantified to what extent light availability and soil moisture on the one hand and seedling size on the other hand control the relationship between branch and stem biomass of European beech and Norway spruce seedlings. Aboveground biomass partitioning of both tree species were influenced by size and to a lesser extent by the environmental conditions. The branch biomass allocation pattern to reduced light and soil moisture differed strongly between the two species. European beech allocation was only driven by size and of Norway spruce by size and the environmental conditions. Overall, beech seedlings seem to have much higher crown plasticity as spruce. Our results indicate that in contrast to above-belowground biomass allocation pattern which depend very much on the environmental conditions, aboveground biomass partitioning seem to be mainly controlled by plant size.