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Interaction of nitrogen supply and water relations in plantation Eucalyptus globulus

Krockenberger, I., White, D., Bell, R.W. and Dell, B. (2000) Interaction of nitrogen supply and water relations in plantation Eucalyptus globulus. In: Soils 2000 : making our science more useable : proceedings of conference Muresk Institute of Agriculture, 11 - 13 July, Northam, WA, Australia pp. 195-198.

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Eucalyptus globulus produces a large canopy area during the early years of establishment, retains foliage even in adverse environmental conditions and maintains turgor at low leaf relative water contents (White et al., 1996). These characteristics confer competitive advantage over other species in its natural habitat, enabling it to rapidly utilise resources in favourable conditions. However, these strategies also render it vulnerable during prolonged soil water deficits in environments of high evaporative demand (White et al., 1996), such as in south-west Australia.

Leaf area is the dominant factor determining transpirational water loss. Modifying leaf area and retention through manipulation of fertiliser application provides an option for tree management where water deficits can impact on tree survival in some years. Nitrogen has particular potential for regulation of canopy size because there is a strong leaf area response to nitrogen and it is often deficient for tree growth in Western Australia, even on soils with a fertiliser history such as ex-farm sites.

Nitrogen affects plant growth directly, principally in two ways- by influencing leaf area and by affecting photosynthetic capacity. Improved nitrogen nutrition results in greater proportional allocation to above-ground biomass (Fabiao et a/., 1995). Leaves respond to increased nitrogen availability by greater partitioning of nitrogen to the photosynthetic apparatus relative to other leaf components(Lambers eta/., 1998).

Improved nitrogen status resulting in greater leaf area for light interception and a greater capacity for carbon assimilation per unit leaf area potentially leads to a greater subsequent biomass production. However, in seasonally dry environments the potential for greater yield must be considered in the context of increased transpiration due to greater leaf area. Thus, the development of a nitrogen application prescription involves a trade-off between maximising productivity and minimising the risk of drought death.

An experiment investigating the physiological responses of plantation E. globulus to different levels of nitrogen application is being conducted south of Nannup, Western Australia. The initial objective of the project is to quantify the influence of nitrogen supply on carbon assimilation rates, and nitrogen and water use efficiencies at the leaf scale.

Publication Type: Conference Paper
Murdoch Affiliation: School of Biological Sciences and Biotechnology
School of Environmental Science
Publisher: Australian Society of Soil Science Inc (WA Branch) and the Environmental Consultants Association (WA Inc.)
Copyright: © Australian Society of Soil Science Inc (WA Branch)
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