Irrigation with industrial effluent leads to mortality of coppice growth in Eucalyptus

Land disposal of effluent can be an effective and productive method of dealing with wastewater. One approach has been to use fast-growing trees in plantations to transpire large amounts of water and immobilise chemicals. The productivity of these plantations can be enhanced, and hence the rate of water use and chemical immobilisation increased, by felling trees at an early age and regenerating the plantation using coppice growth. Trials were carried out to evaluate the ability of coppice systems to dispose of effluent produced by a food processing factory in south-eastern Queensland. Plantations of Eucalyptus moluccana and E. tereticornis were irrigated with effluent from an early age-once the seedlings were clearly established. Both species grew well and reached a height of about 8 m within 33 months. At this age selected plots of trees of both species were felled and both readily produced coppice. Irrigation of the coppiced and uncut trees continued. After a further 8 months, coppice growth of both species was failing. By contrast, uncut trees remained healthy. The main causes of the failure of coppiced trees appeared to be a combination of acid soils, high soil Al concentrations and high foliar Mn concentrations. The acidification appears to have been induced by nitrification of the ammonium-N applied in the effluent irrigation, while the high Mn reflects both the low soil pH and the reducing conditions induced by waterlogging with high BOD effluent. At this time the uncut trees showed no clear visual signs of stress. There was less waterlogging in the plots with uncut trees and these had lower foliar concentrations of potentially toxic elements. The use of coppice growth in the context of wastewater disposal could potentially remove greater quantities of water and nutrients than established trees. Results here, however, suggest that the coppice growth was more susceptible to unfavourable environmental conditions than normal tree growth and this should be taken into account when choosing a management regime

Growth of tree roots in hostile soil: a comparison of root growth pressures of tree seedlings with peas

Background and Aims: As part of a study on growth of tree roots in hostile soil, we envisaged that establishment and survival of trees on hard, dry soil may depend on their ability to exert axial root growth pressures of similar magnitude to those of the roots of agricultural plants (with significant root thickening when roots grow across an air gap or cracks and biopores). We selected tree species originating from a range of different soil and climatic conditions to evaluate whether their relative success on harsh soil (in an evolutionary sense) might be related to the magnitude of root growth pressures they could exert, or how they performed in the very early stages of growth after germination. Methods: We measured the maximum axial root growth force (Fmax) on single lateral root axes of 3- to 4- month old seedlings of 6 small-seeded eucalypts from 2 different habitats and 2 contrasting soil types. Root growth rate, root diameter and Fmax were also measured on the primary root axes of a large-seeded acacia and a domesticated annual (Pisum sativum) seedling for up to 10 days following germination. Results: The lateral roots of the 6 eucalypts and the primary roots of the acacia were considerably smaller than the primary roots of P. sativum and they exerted average forces of similar magnitude to one another (0.198 to 0.312 N). The maximum axial root growth pressures were all in the range 150 to 250 kPa but E. leucoxylon, E. loxophleba and A. salicina exerted the greatest pressures among the trees, and comparable pressures to those exerted by the primary roots of 2-day-old P. sativum (211-252 kPa). Although the primary roots of acacia seedlings exerted increasing axial root growth pressures over a 10-day period following germination, the pressures were still only slightly greater than those of the domesticated plant, P. sativum. Conclusions: The lack of any very large differences in axial root growth pressures between trees and domesticated plants suggests that trees that grow well in harsh soil don't do so by exerting higher root growth pressures alone but by also exploring the network of cracks and pores more effectively than do other plants that are less successful