Changes in carbon isotope composition during vegetative phase change in a woody perennial plant

摘要

Changes in carbon isotope composition (delta(13)C) and leaf morphology associated with vegetative phase change were monitored in Metrosideros excelsa Sol. ex Gaertn. (family Myrtaceae). Plants of three ontogenetic states were used: juvenile seedlings, micropropagated plants in a rejuvenated state, and reproductively mature plants bearing leaves with adult characteristics. The effects of temperature regime (32/24 degreesC, 24/ 16 degreesC, and 16/ 8 degreesC dayight) and plant architecture (branched and single-stemmed plants) were studied in two separate experiments. Although both juvenile and rejuvenated plants exhibited juvenile leaf morphology at the start of the experiments, there was no difference between leaf delta(13)C in these plants and that in adult plants at this time (mean ca. -27%). Vegetative phase change occurred in juvenile and rejuvenated plants grown at 24/16 degreesC, and there was a corresponding increase in leaf delta(13)C (from ca. -27% to -23%) in these two groups of plants. Leaf delta(13)C in adult plants remained relatively constant (ca. -26%) at 24/16 degreesC. There was little change in leaf delta(13)C in all plant states maintained at 32/24 degreesC or 16/ 8 degreesC, and vegetative phase change did not occur in juvenile and rejuvenated plants grown under these two temperature regimes. Rejuvenated plants grown in a greenhouse also exhibited a progressive development of adult leaf morphology, accompanied by an increase in leaf delta(13)C, an effect that was more pronounced in single-stemmed (from -26.4% to ca. -24%) than in branched plants. It is suggested that increasing delta(13)C in juvenile and rejuvenated plants undergoing phase change is a result of reduced sink strength in single-stemmed plants, and to a lesser extent within each branch of branched plants, causing reduced stomatal conductance and photosynthesis. [References: 27]