Nico E. Marcar

Effects of root-zone solutes on eucalyptus-camaldulensis and eucalyptus-bicostata seedlings - responses to na+, mg2+ and cl

Specific-ion effects in salt-treated eucalypts were examined with two species known to differ in salt tolerance viz. E. camaldulensis (more tolerant) and E. bicostata (less tolerant). Sand-cultured plants were irrigated with different nutrient solutions designed to impose either osmotic stress (concentrated macronutrients with balanced cations and anions) or specific ion stress from either NaCl or MgCl2, or from nutrient solutions rich in particular ions viz. Na+, Mg2+ and Cl- (balancing counter ions were provided in all cases). Half-strength Hoagland nutrient solution served as control. All treatments were applied at osmotic pressures of approximately 0.52 MPa by appropriate concentrations of each solution.In general, salt-induced growth reductions were greater for E. camaldulensis than for E. bicostata, although E. camaldulensis showed strongest exclusion of Na+, Mg2+ and Cl- from shoots. Application of NaCl and concentrated macronutrients resulted in similar growth reductions. E. bicostata seedlings exposed to high Cl- concentrations in the presence of Mg2+ and concentrated cations suffered significantly more shoot and root reduction than those exposed to other salts. Treatment with solution rich in Cl- resulted in extensive leaf damage, which suggested that Cl- may have exerted a specific effect. No specific Na+ effect was observed for either species, even though shoot Na+ concentrations were considerably higher for E. bicostata than for E. camaldulensis. Root growth was considerably less for plants treated with Mg2+ salts and this effect was associated with low root Ca2+ concentrations.

Response of Eucalyptus camaldulensis Dehnh., E. globulus Labill. ssp. globulus and E. grandis W.Hill to excess boron and sodium chloride

In a sand culture experiment we investigated the effects of boron (0.01, 0.19, 0.46 and 0.93 mol m−3 B, as H3BO3), sodium chloride (0, 100 and 200 mol m−3 NaCl) and combined B and NaCl, over 36 days, on growth, water use and foliar ion concentrations of nine week-old seedlings of three fast-growing, commercial eucalypts ( Eucalyptus camaldulensis Dehnh. , E. globulus Labill. ssp. globulus and E. grandis W.Hill.). Shoot dry weight was significantly reduced by high concentrations of NaCl (p < 0.001) and by B and NaCl in combination (p ≤ 0.05) but not by B alone. Root dry weight was significantly reduced by both NaCl (p < 0.001) and B (p < 0.001), but not by combined B and NaCl. Foliar B concentrations increased with higher concentrations of applied B and decreased with higher NaCl concentrations. Foliar Na concentrations were greater with higher NaCl concentrations, whereas B application had no significant effect on foliar Na concentrations. All three species accumulated relatively high B concentrations in leaves. Severe boron toxicity symptoms (BTS) were apparent only when leaf B concentrations exceeded 50 mol x 10−6 g−1, but even at these high concentrations plant growth was only slightly reduced. E. camaldulensis showed least development of BTS, the lowest leaf B concentrations and least reduction in height growth due to B and NaCl. The results suggest that there was a correlation between both B tolerance and B accumulation in leaves and between tolerance to B and NaCl.

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 Symphyomyrtusfollowing the informal classification of the eucalypts by Pryor and Johnson (1971)., 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 Monocalyptusfollowing the informal classification of the eucalypts by Pryor and Johnson (1971). 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.

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.

Analysis of respiratory metabolism correlates well with the response of Eucalyptus camaldulensis seedlings to NaCl and high pH

Growth of sand-cultured Eucalyptus camaldulensis Dehnh. (river red gum) seedlings from six wide-ranging provenances was reduced in the presence of 150 mM NaCl, a high pH of 9.5, and combined NaCl and high pH, compared with no applied NaCl and neutral pH. Effects of these stress conditions on respiration rates and substrate carbon conversion efficiencies of rapidly-expanding leaf tissue were measured with calorespirometric techniques. Growth rates were calculated from respiration parameters. Respiration rate, measured as metabolic heat production rate (q), showed no consistent trend with either NaCl or high pH, whereas the rate measured as CO2 production rate (R CO2) was generally lower with both treatments. The ratio of heat lost per mole of CO2 produced [q/(R CO2)] was consistently increased by both stresses. Stress causes a larger fraction of metabolic energy produced by aerobic metabolism to be lost as heat, relative to non-stressed controls. Consequently, a larger fraction of photosynthetic product in stressed seedlings must be metabolized to CO2 per mole of C incorporated into biomass. Our results indicate that 0.42 mol substrate C is converted to CO2 per mole C incorporated into biomass for control plants, compared with 0.96 mol for plants treated with combined NaCl and high pH. Respiratory responses to treatment varied with provenance. Specific growth rates, calculated from repiratory parameters (q and RCO2) of stressed E. camaldulensis seedlings, generally paralleled experimentally-determined reduced growth (dry weight) of these seedlings. Thus, measurements of leaf respiration allow calculation of growth inhibition caused by NaCl and high pH stress. However, we could not discriminate among provenances in this experiment with only one level of NaCl and pH.

Eucalypt Taxa for Low- to Medium-rainfall Farm Forestry in South-Eastern Australia

Summary Enhanced knowledge of on-farm forestry opportunities in the low to medium (500–750 mm) mean annual rainfall zone of south-eastern Australia is needed to maximise commercial and environmental benefits. Key research issues include species and provenance selection, site preparation and silviculture. As part of the ‘Heartlands Initiative’, CSIRO established several taxa evaluation trials in southern NSW and northern Victoria (within the Murray Darling Basin) in 2002. Results from four of these trials, comprising 16 taxa, are presented. Large differences in survival were evident amongst sites and species. Mean survival after 5 y was highest (89%) at Coomalong (near Violet Town, north-eastern Victoria), followed by Brooklyn West (near Wagga Wagga, NSW; 85%), Byawatha Hills (near Springhurst, north-eastern Victoria; 76%) and Koora (near Holbrook, NSW; 54%). Mean stem diameter and calculated stem volume at 5 y were greatest at Coomalong, but mean height was similar at the three sites. Survival of the commercial Eucalyptus camaldulensis × E. globulus hybrid clone, E. cladocalyx, E. argophloia and E. camaldulensis was consistently high. Eucalyptus camaldulensis × E. globulus hybrid clone had the best growth across all sites, followed by E. benthamii, E. botryoides and Corymbia maculata. Best tree form was achieved by E. camaldulensis × E. grandis, E. camaldulensis × E. globulus, E. benthamii, C. maculata and C. variegata. Growth of E. crebra was consistently poorest, with E. occidentalis also having slow growth and poor form. Selection of suitable taxa and best-practice establishment and silviculture are critical to establishing good plantations on these sites.

Farm forestry options for saline environments

Farm forestry can contribute substantially to managing the rise of saline ground water and productively using saline land. The capacity of trees to survive and grow on saline land is influenced by species and provenance used, site factors such as seasonal waterlogging, and appropriate management techniques that limit root-zone salt accumulation. Groundwater use is enhanced when water tables are not too saline (EC [electrical conductivity] < 10 dS/m [deciSeimens per metre]) and not too deep ( < 4–5 m). There are good prospects to enhance tree growth on saline land through exploitation of genetic variation within species, such as E. camaldulensis (river red gum), by producing improved seed and also through inter-specific hybrids. Examples of outcomes from research into genotype evaluation and tree water use under saline conditions in Australia and Pakistan are provided. For example, whilst commercial tree species such as Eucalyptus globulus (southern blue gum) and E. grandis (flooded gum) are slightly salt-tolerant, species such as E. occidentalis (swamp yate) and Acacia nilotica (babul) are highly tolerant. Prior to large-scale implementation of farm forestry in saline environments, a better understanding is required of spatial and temporal impacts of tree plantings on ground water movements. Tree growth and water use responses to salinity also warrant further investigation.

Prospects for Managing Salinity in Southern Australia Using Trees on Farmland

Trees are typically planted in salt-affected agricultural landscapes of southern Australia for environmental and economic benefit. Environmental benefits include land reclamation and containing groundwater rise, reducing salt loads in streams, carbon sequestration, and enhanced biodiversity. Most efforts have concentrated on managing dryland (rainfed) catchments where recharge (water intake) and discharge (water outflow) locations are usually well defined. Trees are typically planted in agroforestry, compact plantation, or shelterbelt configurations mostly in recharge areas or upslope of discharge areas and, less commonly, to stabilize discharge areas. In saline discharge areas, the amount and concentration of salt to which tree roots may be exposed varies with landscape position, salt load in the soil regolith, management practices, the extent of lateral subsurface flow of water, and the degree to which saline soil water and groundwater are used by trees. Tree survival and growth are progressively decreased at higher soil and groundwater salinities, with the extent of this reduction depending on tree species’ (genotype) tolerance to salinity and associated stresses, such as waterlogging and sodicity. Several Australian native tree species, including Eucalyptus camaldulensis, E. occidentalis, and E. spathulata perform consistently well on saline soils. The use of selected eucalypt hybrid clones may enhance prospects for more economically productive farm forests on saline land. Saline water tables are more likely to be lowered by planting trees in saline areas if trees are planted at an appropriate scale and can reduce recharge and/or use groundwater directly. Opportunities to lower the water table beneath a plantation are greater if lateral flows from surrounding areas are relatively small. However, if the aim is to maximize the use of groundwater by trees for improved tree growth and environmental outcomes, then lateral flow from the surroundings could be an advantage. Case studies are provided from several regions in southern Australia from field experiments and process-based modeling to illustrate growth and water use responses to salinity, opportunities for maintaining water quality of rivers and streams in salinized catchments, and for both utilising and stabilizing salt-affected land in dryland and irrigated situations.

Predicting Growth, Carbon Sequestration and Salinity Impacts of Forestry Plantations

Farm forestry is an increasingly important form of diversifying farm income and helping to deal with environmental issues including dryland salinity, global warming and climate variability. Here we briefly describe the development, use and spatial application of improved versions of the plantation growth model, 3-PG, to provide estimates of productivity and carbon sequestration as well as salinity impacts. Several forestry scenarios using eucalypt species and Pinus radiata were tested with application to the Corangamite Catchment in south western Victoria, Australia.