Growth and biomass partitioning of northern red oak and yellow- poplar seedlings: effects of shading and grass root competition

Seedling growth of Quercus rubra and Liriodendron tulipifera were compared under conditions of grass root competition (Poa pratensis). Total seedling biomass of oak was greater than yellow-poplar in all environments and harvests because of an initial growth advantage from larger seed reserves, but biomass relative growth rate of yellow-poplar was greater than oak in all environments. Grass root competition reduced biomass of both species, but more for yellow-poplar. In the absence of grass, shading reduced biomass of both species, especially yellow-poplar; shading in the presence of grass resulted in a nonsignificant increase in biomass of both species. Shoot-root ratio and partitioning of leaf and root biomass to surface area for yellow-poplar was always greater than oak. In response to competition for soil reosurces, both species increased biomass partitioning to the root at the expense of the shoot. In response to shading, yellow-poplar increased leaf area proportion; oak did not. Thinner leaves and a more fibrous root system were more important in explaining yellow-poplar's higher relative growth rate under conditions of shading and root competition compared to oak than differences in shoot-root weight ratio or plasticity in biomass partitioning. -from Authors