Growth Performance and Physiological Characteristics of Four Clones of Eucalypt Seedlings under Different Light Intensities

Abstract

The growth performance and physiological characteristics of four clones of eucalypt seedlings were studied under different light conditions at the nursery in the Faculty of Forestry, Kasetsart University, Bangkok. A 4 × 2 factorial design in RCBD with two factors namely, four clones of eucalypt (K7, K51, K59 and K7) and two light intensities (30 and 100%) was applied with three replications. Growth, biomass, leaf chlorophyll content and photosynthetic light response were undertaken six months after the experiment.

The results showed that the growth and seedling biomass of various parts except for leaf and root biomass were significantly influenced by light intensity, while only the height growth and leaf and root biomass were significantly different among clones. Differences in the shoot/root ratio were also significant among clones, indicating variation in seedling form due to genetic background. The leaf chlorophyll analysis showed a significant difference between clones, and seedlings raised under low light conditions had greater leaf chlorophyll content compared with those under full sunlight. There was also a clear difference due to the interaction between light intensities and clones.

The analysis of photosynthetic light response indicated similar patterns among treatments but the light-saturated gross photosynthesis varied significantly with light conditions and clones. In contrast, dark respiration only responded noticeably to light intensities. The findings suggest that clone K7 tended to be more shade tolerant compared with the others, thereby making it more suitable to be planted with narrow spacing and/or in a shady environment.

Keywords: growth and physiology, eucalypt seedling, light intensity