Growth and physiological performance of controlled Acacia auriculiformis x A. mangium hybrids
2002
Sapit Royampaeng(Royal Forest Department, Bangkok (Thailand). Forest Research Office. Silviculture Research Division) E-mail:Sapitr@forest.go.th
Objective of the present study was to investigate the growth performance and physiological adaptations to seasonal drought of the controlled Acacia auriculiformis x A. mangium hybrids growing in Darwin, the wet-dry tropical region of Australia, compared to the parental species. Particularly, photosynthesis and related parameters in response to seasonal drought and their relationship with growth performance were discussed. A. auriculiformis, A. mangium and the A. auriculiformis x A. mangium hybrids showed significant differences in growth and canopy size, and physiological adaptation to seasonal drought. At 25 months old, the hybrids were superior in height and diameter growth to both the parental species but, in stem volume determinations, they were superior only to A. auriculiformis. Canopy phyllode area appeared to be a good indicator for growth in these acacias. Furthermore, larger canopy size of A. mangium and the hybrids was supported by greater specific phyllode area (SLA), thereby producing individual phyllodes with lower cost. The phyllode photosynthetic activity of the three acacias declined in the dry season and the physiological responses under drought condition were significant differences. Among the three species, A. auriculiformis and the hybrids had greater phyllode photosynthetic activity in the dry season. Within species, the NT genotype of the hybrids and A. auriculiformis was better able to maintain high photosynthesis at low soil water availability. On the other hand, the QLD genotype of these species was able to maintain high photosynthetic activity comparable to the NT genotype, presumably by retaining high soil water over the root zone. The available evidence suggests that this may possibly be genetically determined at the maternal level. Further studies are needed to evaluate their potential in future genetic improvement programs.
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