Andrew Callister

Water stress impacts on respiratory rate, efficiency and substrates, in growing and mature foliage of Eucalyptus spp

In previous studies, water stress has induced variable and sometimes contradictory changes in respiration. We used isothermal calorimetry to measure the response of foliar respiration to water deficit in nine eucalypt genotypes. Specific growth rates (RSG) of shoots and leaves of variable age were measured independently, and the data were applied to both the growth-maintenance and enthalpy balance models. We calculated the oxidation state of respiratory substrate and the enthalpy change for the conversion of substrate carbon to biomass (ΔHB). Moderate water stress reduced the RSG of shoots by 38% (P<0.01) and carbon conversion efficiency by 15% (P<0.05). The relationship between carbon conversion efficiency and RSG was not affected by water deficit for shoots, but was significantly altered for leaves. Water deficit increased maintenance respiration by about 23% (P<0.001). The growth coefficient of respiration was not significantly altered. However, changes in oxidation states of substrate and biomass suggest that the energy requirements of biosynthesis were increased under water stress. Our results confirm that carbohydrates are the major respiratory substrates in growing tissues, though mature leaves utilized a substantial component of more reduced substrate. Mature leaves had variable oxidation states for respiration substrate, which indicates a variable relationship between CO2 evolution and ATP production. Measured ΔHB in shoots and leaves were too small for reliable estimation of RSG by the enthalpy balance model. We also found significant effects of water stress on the oxidation state of substrate and ΔHB.

Seasonal changes in carbohydrates, cyclitols, and water relations of 3 field grown Eucalyptus species from contrasting taxonomy on a common site

Abstract• Alterations in plant chemistry underpin a suite of physiological adaptations to arid conditions. Qualitative and quantitative differences in leaf chemistry are found in the genus Eucalyptus correlating with physiological adaptation to aridity.• Here we investigate seasonal water relations of three field grown eucalypt species grown at a common site known to differ in their ability to accumulate the cyclic sugar alcohol, quercitol.• We show that quercitol contributes significantly to osmotic relations in field grown trees of Eucalyptus melliodora but is present only in trace amounts in E. rubida and E. obliqua.• Measured concentrations of quercitol account for the difference in osmotic potentials between species and can be interpreted as a mechanism for adaptation to low water availability.Résumé• Des altérations dans la chimie des plants soutiennent une série d’adaptations physiologiques à l’aridité. Des différences qualitatives et quantitatives dans la chimie des feuilles sont trouvées chez le genre Eucalyptus en corrélation avec les adaptations physiologiques à l’aridité.• Ici, nous étudions les relations hydriques saisonnières de 3 espèces d’Eucalyptus de plein champ, poussant sur un site commun, connues pour être différentes au plan de leur capacité à accumuler le quercitol.• Nous montrons que le quercitol contribue de manière significative aux relations osmotiques chez Eucalyptus melliodora mais est seulement présent à l’état de trace chez Eucalyptus rubida et Eucalyptus obliqua.• Les concentrations de quercitol qui ont été mesurées rendent compte des différences de potentiel osmotique observées entre les espèces et peuvent être interprétées comme un mécanisme d’adaptation à la faible disponibilité en eau.

A form diagram to optimise pruning schedules for eucalypt clear-wood production

Summary Branch pruning is necessary to produce high-value wood products from eucalypt plantations. Four requirements of an effective and efficient pruning regime for clear-wood production are to (a) restrict the pruned-stem diameter to a specified maximum, (b) ensure only green branches are pruned, (c) remove a proportion of the green crown that allows for continued competitiveness of the pruned trees and (d) minimise the number of pruning interventions. In this paper, we present a pruning decision support tool that diagrammatically combines results from growing stands and crown reduction trials. Elements depicting the pruning schedule, target maximum pruned diameter (PDmax), lower height of the green crown (GCLH) and target retained proportion of the green crown (GCRP) are overlaid onto a set of stem-taper curves. The form diagram was demonstrated using data from two adjacent commercial plantations of Eucalyptus pellita (‘Caravan Hill’ and ‘Fishtail’), established in the same planting season, for solid-wood production in northern Queensland, Australia. We fitted a cubic tree taper model that described 89% of the variation in stem diameter at a given height. PDmax was set at 12 cm and GCRP was set at 50%. Pruned height was set at 6 m assuming two lifts. Site differences in E. pellita growth, slenderness and green-crown height resulted in different optimum pruning schedules even on adjacent holdings. Within-stand heterogeneity in slenderness and green-crown height contributed further to the complexity of pruning scheduling. Our results suggest that it would have been necessary to complete the Fishtail site pruning program at the commencement of the second dry season after planting to ensure that the pruned height was always greater than GCLH. On the other hand, the first pruning lift could be conducted at the Caravan Hill site at the same time that the second lift was being completed at Fishtail. Management options that increase the height growth in the first year, promote live crown retention and increase within-stand homogeneity will improve the effectiveness of fixed-lift pruning for eucalypt clear-wood production.