Effects of shading and removal of plant parts on growth of Trema micrantha seedlings

Effects of artificial shading and removal of plant parts on growth of Trema micrantha (L.) Blume (Ulmaceae) seedlings were studied. Seedlings were grown in pots in a greenhouse in 45, 30, 10.6, 4.8 and 1.8% of full sunlight. Shading for 60 days had no effect on survival, but it influenced all growth parameters measured. Total biomass decreased with decreasing irradiance, reflecting reductions in dry mass of leaves, stems and roots. In response to shading, allocation of biomass to leaves increased, while allocation of biomass to roots decreased. Specific leaf area, leaf area ratio and leaf mass ratio increased with decreasing irradiance. Decreases in relative growth rate were caused by reductions in net assimilation rate rather than leaf area ratio. Photosynthetic efficiency, as determined by the Fv/Fm ratio (Fv = variable fluorescence, Fm = maximal fluorescence), was unaffected by the shading treatments. Partial removal of leaves, stem or roots did not affect seedling survival. Seedlings responded to removal of plant parts by compensatory growth. Topophysis was observed when the apex was removed: the lateral buds developed only as new plagiotropic lateral shoots; consequently, the decapitated plant ceased height growth and was unable to compete with its neighbors for light.