Kinetic analysis of nonisothermal differential scanning calorimetry of 1,3-dipalmitoyl-2-oleoylglycerol

The crystallization of fats has been extensively studied because of its importance in the processing of food and food ingredients. Differential scanning calorimetry (DSC) is widely used in such studies. The aim of this study was to examine the determination of kinetic parameters from nonisothermal DSC crystallization of a model fat, 1,3-dipalmitoyl-2-oleoylglycerol. We applied peak and isoconversional methods to determine activation energies and compared these techniques with a nonparametric method, which separates the temperature dependence and degree of crystallization dependence of the crystallization rate. The Johnson-Mehl-Avrami-Erofeyev-Kolmogorov (JMAEK) model provided the best fit to the data, while the temperature dependence of the rate constant was best explained by a Vogel-Fulcher relationship, where the reference temperature was the melting point of the crystallizing species.     

‘Ecological forestry’ and eucalypt forests managed for wood production in south-western Australia

The model of ‘ecological forestry’ has evolved as a part of the development of the concept of ecosystem management. ‘Ecological forestry’ emphasises that manipulation of a forest ecosystem should consider, and as far as practicable work within the limits of, natural disturbance patterns prior to extensive human alteration of the landscape. This paper evaluates the extent to which forest management practices in jarrah (Eucalyptus marginata) and karri (Eucalyptus diversicolor) forests of south-western Australia align with this view of the characteristics and appropriate silviculture of ‘ecological forestry’. Characteristics and appropriate silviculture of ‘ecological forestry’ are evaluated in relation to (i) the stand level decisions of stand structure and harvest timing and (ii) the landscape level decisions of harvest levels and age structures, and spatial patterns of harvest. Forest management in south-western Australia is found to align with appropriate silviculture under this model of ‘ecological forestry’. Additionally, the landscape triad of areas managed to ‘ecological forestry’ principles, conservation reserves and areas managed to production forestry is in place in the south-western forests of Australia. Strengths and weaknesses in the model of ‘ecological forestry’ and the ability to interpret consistency of practices in the forests of south-western Australia with the characteristics of ‘ecological forestry’ are identified.     

Comparison of phospholipid fatty acid (PLFA) and total soil fatty acid methyl esters (TSFAME) for characterizing soil microbial communities

Phospholipid fatty acid (PLFA) and total soil fatty acid methyl esters (TSFAME), both lipid-based approaches used to characterize microbial communities, were compared with respect to their reliable detection limits, extraction precision, and ability to differentiate agricultural soils. Two sets of soil samples, representing seven crop types from California's Central Valley, were extracted using PLFA and TSFAME procedures. PLFA analysis required 10 times more soil than TSFAME analysis to obtain a reliable microbial community fingerprint and total fatty acid content measurement. Although less soil initially was extracted with TSFAME, total fatty acid (FA) content g⁻¹ soil (DW) was more than 7-fold higher in TSFAME- versus PLFA-extracted samples. Sample extraction precision was much lower with TSFAME analysis than PLFA analysis, with the coefficient of variation between replicates being as much as 4-fold higher with TSFAME extraction. There were significant differences between PLFA- and TSFAME-extracted samples when biomarker pool sizes (mol% values) for bacteria, actinomycetes, and fungi were compared. Correspondence analysis (CA) of PLFA and TSFAME samples indicated that extraction method had the greatest influence on sample FA composition. Soil type also influenced FA composition, with samples grouping by soil type with both extraction methods. However, separate CAs of PLFA- and TSFAME extracted samples depicted strong differences in underlying sample groupings. Recommendations for the selection of extraction method are presented and discussed.     

Symptom development and latent period of Austropuccinia psidii (myrtle rust) in relation to host species,temperature, and ontogenic resistance

Myrtle rust (Austropuccinia psidii) is an invasive species causing damage to Myrtaceae species in natural and managed ecosystems in many countries. To better understand myrtle rust epidemiology we studied latent period (LP) and ontogenic resistance in relation to temperature on three susceptible hosts (Metrosideros excelsa, Lophomyrtus bullata × L. obcordata and Syzygium jambos). The latent period curve was U-shaped, with latent development >0 from between 8 and 10 °C, depending on the host, to 32 °C. Optimum range was 22–28 °C with minimum LP of 5–7 days. Peak spore production occurred over about 2 weeks, starting about 1 week after the LP ended. Some spore production continued for 1–2 months. Comparison of the LP data with field temperatures indicated that the uredinial stage of A. psidii can overwinter in the latent phase in temperate areas of New Zealand and southern Australia and, therefore, uredinial or telial reinfection is not required during winter. The LP information was used to correct the LP function in a New Zealand myrtle rust climatic risk model. The transition of emergent leaf and stem tissues in susceptible Myrtaceae genotypes from susceptible to immune (ontogenic resistance) was characterized in terms of uredinium density and LP. Onset of ontogenic resistance was closely linked to the degree of leaf expansion, with fully expanded leaves being immune to infection. Because ontogenic resistance restricts infection to periods when growth flushes occur, understanding it is crucial for explaining the seasonality of myrtle rust development in the natural environment.