Peter Hopmans

Stem deformation in fast grown Pinus radiata: an investigation of causes

Abstract The incidence of deformed stems and poor form of Pinus radiata (D. Don) growing on ex-pasture sites in south-eastern Australia has been termed the Toorour syndrome. The syndrome appears to be under genetic control and stimulated by high nitrification in the soil. The influence of weather conditions, stem structure, nitrogen (N) availability and copper (Cu) supply on the onset of Toorour syndrome was examined. Trees deformed most markedly during a late-spring flush when the weather was warmer, wetter, and windier than previously; there was no distinct meteorological cause, except that strong wind created the mechanical disturbance. During this warm, wet and windy period the form of N in meristematic tissue changed as the trees flushed; the ratio of soluble N to total N dropped dramatically. Concentrations of Cu in buds decreased over time and also were lower in trees that received N and P fertiliser than those that did not. No structural or anatomical differences between form classes were found that could be attributed to the onset of stem bending. Tissue produced prior to deformation in deformed trees did not have lower density, shorter tracheids, or larger microfibril angles. It was not possible to define weather conditions, N availability, or Cu supply to meristematic tissue as a single causative factor in the Toorour syndrome. Many variables changed coincidentally with stem sinuosity, but none were found to be linked clearly and causatively with the syndrome. The nutritional physiology of the syndrome, if one exists, is not much better defined. The question as to whether there is an important and functional difference in nutritional physiology between straight and deformed trees remained unanswered.

Temperature responses are a window to the physiology of dark respiration: differences between CO2 release and O2 reduction shed light on energy conservation.

We showed that temperature responses of dark respiration for foliage of Pinus radiata could be approximated by Arrhenius kinetics, whereby E(0) determines shape of the exponential response and denotes overall activation energy of respiratory metabolism. Reproducible and predictable deviation from strict Arrhenius kinetics depended on foliage age, and differed between R(CO2) and R(O2). Inhibition of oxygen reduction (R(O2)) by cyanide (inhibiting COX) or SHAM (inhibiting AOX) resulted in reproducible changes of the temperature sensitivity for R(O2), but did not affect R(CO2). Enthalpic growth--preservation of electrons in anabolic products--could be approximated with knowledge of four variables: activation energies (E(0)) for both R(CO2) and R(O2), and basal rates of respiration at a low reference temperature (R(REF)). Rates of enthalpic growth by P. radiata needles were large in spring due to differences between R(REF) of oxidative decarboxylation and that of oxygen reduction, while overall activation energies for the two processes were similar. Later during needle development, enthalpic growth was dependent on differences between E(0) for R(CO2) as compared with R(O2), and increased E(0)(R(O2)) indicated greater contributions of cytochrome oxidase to accompany the switch from carbohydrate sink to source. Temperature-dependent increments in stored energy can be calculated as the difference between R(CO2)DeltaH(CO2) and R(O2)DeltaH(O2).

Effects of fire retardant on heathland soils in south-eastern Australia

A study was undertaken to assess the effects of fire retardant application, unmodified by heat of fire, on soil properties in 2 fire-prone heathland communities at Marlo and the Grampians in south-eastern Australia. Fire retardant (Phos-Chek D75-R at 0.144 g/L) was applied at rates of 0.5, 1.0, and 1.5 L/m2 and compared with control treatments of nil and 1.0 L/m2 of water. Monitoring of surface soils showed that pH at both sites decreased while soil salinity increased immediately after application followed by a rapid decline to pre-treatment values within 12 months. The impact of retardant on total carbon and nitrogen was minor and within the range of natural variation of C and N in surface soils at both sites. Levels of readily available or labile forms of N increased at both sites but declined rapidly to background values after 12 months. Applications of retardant progressively increased extractable P in the surface soil at Marlo, in contrast to the Grampians where a rapid increase was observed after two months followed by a decline after 12 months. These results showed a significant increase in labile P in the surface soil after 12 months and also indicated that a large proportion of the phosphate applied had leached into the subsoil. Likewise, fire retardant applied at the highest rate caused increases in labile sulfate after 2 months at both sites, followed by a rapid decline to background levels. It is expected that the elevated levels of soil phosphate in particular could have a long-term impacts on growth and composition of heathland vegetation known to be sensitive to elevated levels of phosphate in soil.