Effect of NaCl and high pH on seedling growth of 15 Eucalyptus camaldulensis Dehnh. provenances

Eucalyptus camaldulensis Dehnh. is a moderately salt-tolerant Australian tree species widely used in farm forestry, often in salt-affected landscapes. In a glasshouse experiment, E. camaldulensis seedlings from 15 wide-ranging Australian seed sources (provenances), were cultured in sand-filled pots and treated for 57 days with control (no added NaCl in tap water, neutral pH), saline (150 mol m^–3 NaCl, stepped high pH (pH 7.6 to 9.5) and combined NaCl and high pH solutions. Significant differences were found among provenances in height and shoot dry weight. Differences in provenance response to treatment were found for dry weight but not for height. Reductions in shoot dry weight due to NaCl and high pH ranged from 42.9% to 82.0% and 4.3% to 51.7% respectively. Provenances from Lake Hindmarsh-SE (Victoria) and Lake Albacutya-N (Victoria) had relatively high tolerance to both stresses whereas those from Lake Albacutya-S (Victoria), Lowan Valley (Victoria), Silverton (New South Wales) and Katherine (Northern Territory) had low tolerance to both stresses. Provenances from De Grey River and Fitzroy River (Western Australia) were most tolerant of high pH. The performance of these provenances in this experiment generally accorded well with that in saline field environments.     

Salt tolerance of frost-resistant eucalypts

Nineteen frost-resistant Eucalyptus species were screened for salt tolerance under glasshouse conditions. This study was undertaken in order to determine the potential of these species for planting on dryland salt-affected sites in the frost-prone Tablelands of south-eastern Australia. Seedlings were established in sand-filled pots and exposed to a step-wise increase in NaCl concentration to a maximum of 500 mol m^–3. Salt tolerance was assessed on the basis of mortality, leaf damage and height growth. All species in the subgenus Symphyomyrtus , particularly those in the Section Maidenaria Series Ovatae, were moderately salt-tolerant (no mortality at 300 mol m^–3 NaCl) whereas those in the subgenus Monocalyptus proved to be very salt-sensitive (no survival at 300 mol m^–3 NaCl). Eucalyptus camaldulensis, E. tereticornis and E. occidentalis were the most salt-tolerant species of those included in this study. Salt-sensitive species had shoot Na⁺ and Cl^– concentrations of up to 2.25 mmol g^–1 dry wt.

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Intra-specific variation for response to salt and waterlogging in <Emphasis Type="Italic">Acacia ampliceps</Emphasis> Maslin seedlings

Salinity is a major form of land degradation worldwide, with seasonal or temporary waterlogging often being an associated issue. Acacia ampliceps is a highly salt-tolerant small tree, naturally-occurring in north-western Australia, which produces abundant biomass with potential for fuelwood and fodder. We investigated the extent of variation amongst provenances and families of A. ampliceps for seedling response to salt and waterlogging. Seven-week old seedlings from 27 families (seven provenances, grouped into two regions), were treated in sand-filled pots in a glasshouse with either mixed salt (S) solutions (150 mol m⁻³ for 14 days, 300 mol m⁻³ for 33 days), waterlogging (W) or combined salt (S) and waterlogging (SW). Only 3% of seedlings died, mostly from the combined salt × waterlogging treatment. Seedlings from the Kimberley region had significantly greater height and shoot biomass than those from the Pilbara. Within these regions, Wave Hill (seedlot 14631) and Halls Creek (15738) provenances had the best growth. Height growth was reduced similarly for S- and W-treated plants, whereas that of SW-treated plants was reduced much more. Salt and waterlogging caused shoot dry weight reduction at harvest of 41 and 46%, respectively, with a slight interaction between salt and waterlogging; SW treated plants were most affected. Generally there were relatively small differences in the growth response of provenances and families to salt, but larger (often highly significant) variation in response to waterlogging. Genotypic variation for shoot and phyllode water content and phyllode number in response to salt and waterlogging was generally small. The good agreement found at the provenance level between seedling growth in this experiment and growth of young trees on saline land in a trial in Pakistan suggests that glasshouse screening may be a useful means for selecting potential provenances for field evaluation.     

Enhanced water use efficiency in a mixed Eucalyptus globulus and Acacia mearnsii plantation

Significant increases in aboveground biomass production have been observed when Eucalyptus is planted with a nitrogen-fixing species due to increased nutrient availability and more efficient use of light. Eucalyptus and Acacia are among the most popular globally planted genera with the area of Eucalyptus plantations alone expanding to over 19 Mha over the past two decades. Despite this, little is known about how nutrition and light availability in mixed-species tree plantations influence water use and water use efficiency (WUE). This study examined to what extent water use and WUE have been influenced by increased resource availability and growth in mixed-species plantations. Monocultures of Eucalyptus globulus Labill. and Acacia mearnsii de Wildeman and 1:1 mixtures of these species were planted. Growth and transpiration were measured between ages 14 and 15 years. Aboveground biomass increment (Mg ha⁻¹) was significantly higher in mixtures (E. globulus; 4.8 + A. mearnsii; 0.9) than E. globulus (3.3) or A. mearnsii monocultures (1.6). Annual transpiration (mm) measured using the heat pulse technique was also higher in mixtures (E. globulus; 285 + A. mearnsii; 134) than in E. globulus (358) and A. mearnsii (217) monocultures. Mixtures exhibited higher WUE than monocultures due to significant increases in the WUE of E. globulus in mixtures (1.69 kg aboveground biomass per cubic metre water transpired) compared to monocultures (0.94). The differences in WUE appear to result from increases in canopy photosynthetic capacity and above- to belowground carbon allocation in mixtures compared to monocultures. Although further studies are required and operational issues need to be resolved, the results of this study suggest that mixed eucalypt–acacia plantations may be used in water-limited environments to produce a given amount of wood with less water than eucalypt monocultures. Alternatively, because mixtures can be more productive and use more water per unit land area (but use it more efficiently), they could be utilized in recharge zones where rising water tables and salinity result from the replacement of vegetation (fast growing trees) that uses higher quantities of water with vegetation (shallow rooted annual crops) that use lower quantities of water.