The morphology and physiology of Eucalyptus camaldulensis seedlings grown from seed collected from two locations in the dry tropics, two in the humid tropics and two in semi-arid Northern Australia were compared in phytotron growth cabinets under well-watered and water-limited conditions and diurnal temperature ranges of 30-25 and 22-15�C. Seedlings from the two locations in each climate resembled each other more closely than they resembled seedlings from the other climates across the range of conditions tested. When water-limited, seedlings from the dry tropical and semi-arid climates had a higher allocation of dry matter to roots than seedlings from the humid tropics. However, those from the dry tropics shed their lower leaves and initiated small-leaved axillary shoots while those from the semi-arid climate retained their leaves and did not produce axillary shoots. In contrast, seedlings from the humid tropics responded by reduced gas (CO2 and H2O) exchange without changes in morphology or allocation of dry matter. These responses are appropriate for growth in each climate and are consistent with observations made on wild trees in the field, on trees in plantations overseas and also with data from seedlings grown in earlier glasshouse experiments.
This experiment was designed to examine the effects of aluminium (A1) on the growth of Pinus radiata (D. Don) and Eucalyptus mannifera subsp, mannifera (Mudie) seedlings in culture solutions in a glasshouse to help explain the failure of radiata pine trees on some acid, low fertility soils in Australia on which the native eucalypts flourish. Aluminium (AI) in culture solution increased the growth of roots and shoots of seedlings of both species but while growth of the eucalypt continued to increase with increases in Al to 2,222 fxM, growth of the pine was largest at 370 IxM AI. In addition to total root length, specific root length (length per unit dry weight), a measure of fineness of the root, increased in the eucalypt seedlings as the substrate AI increased. Growth of the shoots and roots of the pine in the absence of any added A1 was extremely poor suggesting that AI, in low concentrations, may be an essential element or ameliorate some other factors in solution culture at low pH.Root and shoot concentrations of K increased with increasing A1, whilst Ca and Mg concentrations decreased and Mn concentrations were unaffected in both species. Tissue Ca and Mg concentrations were 2 to 3 times higher in the eucalypt seedlings than the pine at all levels of added AI due to greater uptake of these elements by the eucalypt. In contrast, at the highest concentration of A1 in the medium, shoot A1 concentrations were lower in the eucalypt than in the pine due to a greater proportion of Al being retained in the eucalypt roots.These differences between the seedlings in terms of root growth and tissue cation concentrations may help explain the ability of eucalypt species to maintain vigorous growth on acid soils high in A1 and low in Ca and P, where growth of the pines failed.
Seedlings of Eucalyptus globulus Labill subsp. globulus grown in soil in pots in the greenhouse grew faster than seedlings of E. globulus subsp. bicostata, and responded better to added nutrients and water. However, water stress caused a greater reduction in the growth of shoots and roots, and in the root/shoot ratios of fertilized seedlings of subsp. globulus than in those of bicostata. More leaf surface wax was produced by seedlings grown in the presence of fertilizer and an adequate supply of water than by seedlings subjected to nutrient or water stress. Despite larger amounts of leaf surface wax, seedlings of subsp. bicostata had higher epidermal conductances than seedlings of subspecies globulus. However, epidermal conductances were reduced more by water stress and by fertilization in seedlings of subsp. bicostata than in subsp. globulus. Tissue osmotic potentials at full and zero turgor were reduced by water stress only in seedlings of subsp. bicostata and were increased by fertilizer only in seedlings of subsp. globulus. The results indicate that although seedlings of subsp. globulus have inherently higher growth rates, seedlings of subsp. bicostata are better adapted to drought.
We examined the hydraulic architecture of Eucalyptus camaldulensis seedlings from two climatically different provenances: Petford in north Queensland, which is humid; and Tennant Creek in the Northern Territory, which is semi-arid. Xylem liquid specific permeability (Kg) was calculated from measurements of xylem air permeability (Kg) and hydraulic resistances (R) were also calculated. Embolism susceptibility curves were constructed by measuring Kg in the stems of young seedlings. Canopy leaf areas were mapped and sap flows through the Tennant Creek and Petford seedlings were simulated. Results showed that the permeability of stem wood in the Tennant Creek seedling was about 40% higher than in Petford, and the permeability of its branch wood was about 25% higher. The threshold water potential for initiation of embolisms (Ψt) was slightly lower in Tennant Creek seedlings (- 3.3 MPa compared with - 3.0 MPa) and the number of embolisms with decreasing Ψ was lower for Tennant Creek seedlings. Sap flow simulations showed differences in the distribution of water throughout the seedling canopies. The results are discussed in terms of the ecology of the two eucalypt provenances.
Distribution of Na+, Cl-, K+, Ca2+ and Mg2+ was studied in individual organs of two highly tolerant and one moderately tolerant species of Casuarina. The highly tolerant species (C. equisetifolia and C. glauca) accumulated little Na+ and Cl- in their shoots and the concentrations of Na+ and Cl- decreased from old to young growing needles. The concentrations of Na+ and Cl- were much higher in shoots of the moderately tolerant species (C. cunninghamiana) and a concentration gradient between old and young needles was not observed. The same pattern of distribution of Cl- in C. equisetifolia was found in seedlings exposed to both short term (13 days at 100 mol m-3 NaCl in solution culture), and long term (6 months at 250 mol m-3 NaCl in sand culture) salinisation. The three species showed little difference in their root ion concentrations. A time sequence experiment of Cl- uptake indicated that the better exclusion of Cl- from the shoots of C. equisetifolia than C. cunninghamiana was due to a lower rate of Cl- uptake and lower net transport into the shoot rather than to its retention in the roots, or reabsorption at the proximal root or hypocotyl.
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