Effects of Shade on Gas Exchange and Growth in Seedlings of Eucalyptus grandis Hill ex Maiden

Abstract

E. grandis seedlings grown under conditions of high (12.6) and low (2.8 Em^-2 day^-) daily integrals of photon flux density exhibited the same light response of photosynthesis when the rates were expressed on a unit leaf volume basis. The conversion of photosynthetic substrate to dry matter was more efficient in larger than in smaller plants.

Allocation of dry matter between leaves, stem and roots was influenced relatively little by the shading treatments, but the utilization of dry matter by the leaves and stem was affected. Plants raised under low light exhibited significantly greater areas per unit weight of leaf, and significantly greater lengths per unit weight of stem than did plants raised in the high-light treatment. Adaptation to shading in E. grandis seedlings was judged to be limited. A model was constructed which described adequately the growth of these seedlings after the age of about 14 days.