Genetic Variation in Flowering Traits of Tasmanian Leptospermum scoparium and Association with Provenance Home Site Climatic Factors.

Leptospermum scoparium is emerging as an economically important plant for the commercial production of manuka honey and essential oils, both exhibiting unique antibacterial attributes. To support its domestication this is the first quantitative genetic study of variation for L. scoparium traits. It utilised plants from 200 open-pollinated families derived from 40 native populations, from across the species range in Tasmania, grown in a common garden field trial. The traits studied were survival, growth, and the flowering traits precocity, the timing of seasonal peak flowering, flowering duration, and flowering intensity. Significant genetic variation was evident at the population level for all traits studied and at the family level for three traits-growth, flowering precocity, and time to peak flowering. These three traits had moderate to high narrow-sense heritability estimates ranging from 0.27 to 0.69. For six of the traits studied, population differences were associated with climate attributes at the locations where seed was collected, suggesting adaptation to the local climate may have contributed to the observed population differentiation. Population level geographical trends suggest that genotypes to focus on for domestication originate from the eastern half of Tasmania for precociousness and the western half of Tasmania for earlier time to peak flowering and extended flowering duration.

Role of corticular photosynthesis following defoliation in Eucalyptus globulus.

Defoliation can reduce net fixation of atmospheric CO(2) by the canopy, but increase the intensity and duration of photosynthetically active radiation on stems. Stem CO(2) flux and leaf gas exchange in young Eucalyptus globulus seedlings were measured to assess the impact of defoliation on these processes and to determine the potential contribution of re-fixation by photosynthetic inner bark in offsetting the effects of defoliation in a woody species. Pot and field trials examined how artificial defoliation of the canopy affected the photosynthetic characteristics of main stems of young Eucalyptus globulus seedlings. Defoliated potted seedlings were characterized by transient increases in foliar photosynthetic rates and concomitant decreases in stem CO(2) fluxes (both in the dark and light). Defoliated field-grown seedlings showed similar stem CO(2) flux responses, but of reduced magnitude. Despite demonstrating increased re-fixation capability, defoliated potted-seedlings had slowed stem growth. The green stem of seedlings exhibited largely shade-adapted characteristics. Defoliation reduced stem chlorophyll a/b ratio and increased carotenoid concentration. An increased capacity to re-fix internally respired CO(2) (up to 96%) suggested that stem re-fixation represents a previously unexplored mechanism to minimize the impact of foliar loss by maximizing the contribution of all photosynthetic tissues, particularly for young seedlings.

Daily patterns of stem size variation in irrigated and unirrigated Eucalyptus globulus.

High resolution measurements of stem diameter variation provide a means to study short-term dynamics of tree growth and water status. In this 14-month study, daily changes in stem radius of Eucalyptus globulus Labill. seedlings were measured with electronic point dendrometers in a plantation in southern Tasmania, Australia. The daily patterns of stem expansion and shrinkage were classified into three phases: shrinkage; recovery; and increase in diameter from one maximum to the next, or increment. This study showed that rapid onset of even mild drought in irrigated trees caused distinct changes in daily patterns of stem diameter variation, particularly the duration of daily stem increment. The duration of the daily increment phase was directly related to increment magnitude. The dynamics of daily increment were significantly affected by mean minimum temperature, indicating a temperature limitation on metabolic processes underlying diameter growth in these trees. Most likely due to differences in conductance, the duration but not rate of the incremental daily expansion was greater in fast- than in slow-growing trees.

Ecophysiological responses of a young blue gum (Eucalyptus globulus) plantation to weed control.

Early weed control may improve the growth of forest plantations by influencing soil water and nutrient availability. To understand eucalypt growth responses to weed control, we examined the temporal responses of leaf gas-exchange, leaf nitrogen concentration (N) and water status of 7-month-old Eucalyptus globulus L. trees in a paired-plot field trial. In addition, we monitored the growth, leaf N and water status of the competing vegetation in the weed treatment. By the end of the 11-month experiment, complete weed control (WF treatment) of largely woody competitors increased the basal diameter of E. globulus by 14%. As indicated by pre-dawn water potentials of > - 0.05 MPa, interspecies competition for water resources was minimal at this site. In contrast, competition for N appeared to be the major factor limiting growth. Estimations of total plot leaf N (g m(-2) ground) showed that competing vegetation accounted for up to 70% of the total leaf N at the start of the trial. This value fell to 15% by the end of the trial. Despite increased leaf N(area) in WF trees 5 months after imposition of weed control, the photosynthetic capacity (A(1500)) of E. globulus was unaffected by treatment suggesting that the growth gains from weed control were largely unrelated to changes in leaf-level photosynthesis. Increased nutrient availability brought about by weed control enabled trees to increase investment into leaf-area production. Estimates of whole-tree carbon budget based on direct measurements of dark respiration and A(1500) allowed us to clearly demonstrate the importance of leaf area driving greater productivity following early weed control in a nutrient-limited site.