Scott A. Dalzell

Bio: Scott A. Dalzell is an academic researcher from University of Queensland. The author has contributed to research in topics: Leucaena & Leucaena leucocephala. The author has an hindex of 15, co-authored 51 publications receiving 607 citations.

A rapid method for the measurement of Leucaena spp. proanthocyanidins by the proanthocyanidin (butanol/HCl) assay

Abstract: Proanthocyanidin (PA) extraction, sample preparation and proanthocyanidin assay (butanol/HCl) reaction conditions were evaluated for measuring PA in Leucaena spp leaf material. The optimal conditions for extracting PA from leaf tissue are described, with short sequential sonications in 70% aqueous acetone being as efficient as prolonged sequential mechanical agitation. In methanol–based extracts, after back extraction to remove pigments, increasing the water content of the reagent/sample matrix suppressed colour development. The addition of low concentrations of Fe3+ to the butanol/HCl reagent enhanced colour yield, but higher Fe3+ concentrations suppressed colour development. The presence of ascorbic acid in the sample extract was shown to increase colour development. Varying the reagent: sample extract ratio from 4:1 to 6:1 significantly decreased colour yield, but neither ratio was different from 5:1. Optimum conditions for the PA assay were as follows: a water content of 8%, the omission of Fe3+, a reagent: sample extract ratio of 5:1 and the addition of ascorbic acid to the stock PA standard solution to match that contributed by the extract in the final mixture. Sample preparation procedures, using back extraction to remove pigments and non-PA phenolics with diethyl ether and ethyl acetate, respectively, were time-consuming and subject to PA losses. The measurement of PA directly in the 70% aqueous acetone extract eliminated these PA losses, but the PA assay required additional optimisation for direct analysis of crude acetone extracts. In the final optimised procedure, PA was extracted by sequential sonication with 70% aqueous acetone containing 5·26 mM sodium metabisulphite as the antioxidant. These extracts were directly analysed by the butanol/HCl reaction using a reagent: sample extract ratio of 5:1, the omission of Fe3+ from the butanol/HCl reagent and the addition of sodium metabisulphite to match that contributed by the extract. This produced consistent linear calibration curves over the range 25–1000 μg PA with an average recovery of 101%. © 1998 Society of Chemical Industry.

Production, economic and environmental benefi ts of leucaena pastures

Abstract: The rate of adoption of leucaena (Leucaena leucocephala)-grass pastures is rising rapidly in northern Australia as graziers realise the extent of the triple-bottom-line benefi ts. Leucaena pastures are suited to >13 M ha of Queensland, with a current estimated 150 000 ha producing 37 500 kg of liveweight gain valued at >$69 M each year. Despite high costs of establishment, this area is expected to expand to 300 000–500 000 ha by 2017. The main factor driving high levels of adoption is the ability of leucaena pastures to meet graziers’ needs for a highly productive and profi table system that meets market requirements for grass-fed beef of superior quality. Production benefi ts include: increased animal production/ ha (up to 4-fold) resulting from a combination of greater animal liveweight gains and increased carry ing capacity; longevity (30–40 yr); and potential to intensify production within the constraints of recent changes to the Queensland Vegetation Management Act and escalating land prices. Other benefi ts are: increased marketing fl exibility; superior capital appreciation of leucaena pastures; and positive animal welfare outcomes. Social factors are also important, with many farmers converting marginal dryland cropping cultivation to leucaena pasture owing to concerns about the impact of drought, global warming, and decreased profi tability and sustainability of dryland farming. Importantly, technical information regarding the establishment and management of leucaena pastures is now available to graziers, giving them the confi dence to adopt the technology. Environmental benefi ts include: dryland salinity mitigation; soil erosion control and improved water quality; improved soil fertility through biological nitrogen fi xation; and greenhouse gas mitigation. Given an average season, existing leucaena pastures fi x approximately 7500 t N and reduce cattle methane emissions by approximately 91 000 t carbon dioxide equivalent carbon (CO 2 -e) annually. These pastures also have the potential to sequester >4 M t of CO 2 -e. However, leucaena is an environmental weed in northern Australia, largely as a result of its historical introduction and use as an ornamental and for slope stabilisation. While most current weed infestations are not due to grazier plantings, a voluntary Code of Practice, where graziers take responsibility for any spread from their properties, has been developed to limit seed production and dispersal. Soil acidifi cation will not be a problem on the alkaline clay soils (high pH buffering capacity) in Queensland where most leucaena pastures are planted. There is need for greater factual appreciation of the environmental aspects of large-scale leucaena plantings, and for a thorough cost:benefi t analysis to be conducted.

Prevalence of mimosine and DHP toxicity in cattle grazing Leucaena leucocephala pastures in Queensland, Australia

Abstract: A postal survey of the level of awareness of leucaena toxicity and an on-farm study of the toxicity status of Queensland cattle herds grazing leucaena were conducted to investigate the prevalence of mimosine and dihydroxypyridine (DHP) toxicity in Queensland. In total, 195 of 356 graziers surveyed responded to the postal survey. Sixty-three percent had inoculated their cattle with in vitro Synergistes jonesii inoculum (produced in an anaerobic fermenter) and 30% of these had inoculated more than once. The remainder used inappropriate procedures. Many graziers (43%) had occasionally observed toxicity symptoms of hair loss and poor animal growth rates. In the on-farm study, the toxicity status of 385 animals in 44 individually managed herds on 36 properties was determined by urine analysis of mimosine and DHP concentrations. No animals were experiencing mimosine toxicity, based on low concentrations of this compound found in the urine. Using the criterion that average herd urine concentrations of DHP >100 μg/mL was indicative of subclinical toxicity, 48% of herds were exposed to subclinical toxicity due to dominant 3,4-DHP (21%) or dominant 2,3-DHP (27%) toxicity; many of these herds had been inoculated with S. jonesii and were thought to be protected. The finding that 27% of herds were excreting high concentrations of 2,3-DHP was unexpected. Statistical analysis of herd-management data revealed that the method used by graziers to inoculate their herds was significantly (P < 0.05) but weakly linked to herd protection status. It was concluded that subclinical 3,4-DHP and 2,3-DHP toxicity remains a problem in Queensland and is likely to be limiting animal production in a significant number of cattle grazing leucaena-grass pastures.

Proanthocyanidins--a final frontier in flavonoid research?

Abstract: Proanthocyanidins are oligomeric and polymeric end products of the flavonoid biosynthetic pathway. They are present in the fruits, bark, leaves and seeds of many plants, where they provide protection against predation. At the same time they give flavor and astringency to beverages such as wine, fruit juices and teas, and are increasingly recognized as having beneficial effects on human health. The presence of proanthocyanidins is also a major quality factor for forage crops. The past 2 years have seen important breakthroughs in our understanding of the biosynthesis of the building blocks of proanthocyanidins, the flavan-3-ols (+)-catechin and (-)-epicatechin. However, virtually nothing is known about the ways in which these units are assembled into the corresponding oligomers in vivo. Molecular genetic approaches are leading to an understanding of the regulatory genes that control proanthocyanidin biosynthesis, and this information, together with increased knowledge of the enzymes specific for the pathway, will facilitate the genetic engineering of plants for introduction of value-added nutraceutical and forage quality traits.

Tannins in nutrient dynamics of forest ecosystems- a review

Abstract: Tannins make up a significant portion of forest carbon pools and foliage and bark may contain up to 40% tannin. Like many other plant secondary compounds, tannins were believed to function primarily as herbivore deterrents. However, recent evidence casts doubts on their universal effectiveness against herbivory. Alternatively, tannins may play an important role in plant–plant and plant–litter–soil interactions. The convergent evolution of tannin-rich plant communities on highly acidic and infertile soils throughout the world, and the intraspecific variation in tannin concentrations along edaphic gradients suggests that tannins can affect nutrient cycles. This paper reviews nutrient dynamics in forest ecosystems in relation to tannins. Tannins comprise a complex class of organic compounds whose concentration and chemistry differ greatly both among and within plant species. Because the function and reactivity of tannins are strongly controlled by their chemical structure, the effects of tannins on forest ecosystem processes are expected to vary widely. Tannins can affect nutrient cycling by hindering decomposition rates, complexing proteins, inducing toxicity to microbial populations and inhibiting enzyme activities. As a result, tannins may reduce nutrient losses in infertile ecosystems and may alter N cycling to enhance the level of organic versus mineral N forms. The ecological consequences of elevated tannin levels may include allelopathic responses, changes in soil quality and reduced ecosystem productivity. These effects may alter or control successional pathways. While a great deal of research has addressed tannins and their role in nutrient dynamics, there are many facets of tannin biogeochemistry that are not known. This lack of information hinders a complete synthesis of tannin effects on forest ecosystem processes and nutrient cycling. Areas of study that would help clarify the role of tannins in forest ecosystems include improved characterization and quantification techniques, enhanced understanding of structure-activity relationships, investigation of the fate of tannins in soil, further determination of the influence of environmental factors on plant tannin production and decomposition, and additional information on the effects of tannins on soil organisms.

Role of anthocyanidin reductase, encoded by BANYULS in plant flavonoid biosynthesis.

Abstract: Condensed tannins (CTs) are flavonoid oligomers, many of which have beneficial effects on animal and human health. The flavanol (-)-epicatechin is a component of many CTs and contributes to flavor and astringency in tea and wine. We show that the BANYULS (BAN) genes from Arabidopsis thaliana and Medicago truncatula encode anthocyanidin reductase, which converts anthocyanidins to their corresponding 2,3-cis-flavan-3-ols. Ectopic expression of BAN in tobacco flower petals and Arabidopsis leaves results in loss of anthocyanins and accumulation of CTs.

Legumes for mitigation of climate change and the provision of feedstock for biofuels and biorefineries. A review

Abstract: Humans are currently confronted by many global challenges. These include achieving food security for a rapidly expanding population, lowering the risk of climate change by reducing the net release of greenhouse gases into the atmosphere due to human activity, and meeting the increasing demand for energy in the face of dwindling reserves of fossil energy and uncertainties about future reliability of supply. Legumes deliver several important services to societies. They provide important sources of oil, fiber, and protein-rich food and feed while supplying nitrogen (N) to agro-ecosystems via their unique ability to fix atmospheric N2 in symbiosis with the soil bacteria rhizobia, increasing soil carbon content, and stimulating the productivity of the crops that follow. However, the role of legumes has rarely been considered in the context of their potential to contribute to the mitigation of climate change by reducing fossil fuel use or by providing feedstock for the emerging biobased economies where fossil sources of energy and industrial raw materials are replaced in part by sustainable and renewable biomass resources. The aim of this review was to collate the current knowledge regarding the capacity of legumes to (1) lower the emissions of the key greenhouse gases carbon dioxide (CO2) and nitrous oxide (N2O) compared to N-fertilized systems, (2) reduce the fossil energy used in the production of food and forage, (3) contribute to the sequestration of carbon (C) in soils, and (4) provide a viable source of biomass for the generation of biofuels and other materials in future biorefinery concepts. We estimated that globally between 350 and 500 Tg CO2 could be emitted as a result of the 33 to 46 Tg N that is biologically fixed by agricultural legumes each year. This compares to around 300 Tg CO2 released annually from the manufacture of 100 Tg fertilizer N. The main difference is that the CO2 respired from the nodulated roots of N2-fixing legumes originated from photosynthesis and will not represent a net contribution to atmospheric concentrations of CO2, whereas the CO2 generated during the synthesis of N fertilizer was derived from fossil fuels. Experimental measures of total N2O fluxes from legumes and N-fertilized systems were found to vary enormously (0.03–7.09 and 0.09–18.16 kg N2O–N ha−1, respectively). This reflected the data being collated from a diverse range of studies using different rates of N inputs, as well as the large number of climatic, soil, and management variables known to influence denitrification and the portion of the total N lost as N2O. Averages across 71 site-years of data, soils under legumes emitted a total of 1.29 kg N2O–N ha−1 during a growing season. This compared to a mean of 3.22 kg N2O–N ha−1 from 67 site-years of N-fertilized crops and pastures, and 1.20 kg N2O–N ha−1 from 33 site-years of data collected from unplanted soils or unfertilized non-legumes. It was concluded that there was little evidence that biological N2 fixation substantially contributed to total N2O emissions, and that losses of N2O from legume soil were generally lower than N-fertilized systems, especially when commercial rates of N fertilizer were applied. Elevated rates of N2O losses can occur following the termination of legume-based pastures, or where legumes had been green- or brown-manured and there was a rapid build-up of high concentrations of nitrate in soil. Legume crops and legume-based pastures use 35% to 60% less fossil energy than N-fertilized cereals or grasslands, and the inclusion of legumes in cropping sequences reduced the average annual energy usage over a rotation by 12% to 34%. The reduced energy use was primarily due to the removal of the need to apply N fertilizer and the subsequently lower N fertilizer requirements for crops grown following legumes. Life cycle energy balances of legume-based rotations were also assisted by a lower use of agrichemicals for crop protection as diversification of cropping sequences reduce the incidence of cereal pathogens and pests and assisted weed control, although it was noted that differences in fossil energy use between legumes and N-fertilized systems were greatly diminished if energy use was expressed per unit of biomass or grain produced. For a change in land use to result in a net increase C sequestration in soil, the inputs of C remaining in plant residues need to exceed the CO2 respired by soil microbes during the decomposition of plant residues or soil organic C, and the C lost through wind or water erosion. The net N-balance of the system was a key driver of changes in soil C stocks in many environments, and data collected from pasture, cropping, and agroforestry systems all indicated that legumes played a pivotal role in providing the additional organic N required to encourage the accumulation of soil C at rates greater than can be achieved by cereals or grasses even when they were supplied with N fertilizer. Legumes contain a range of compounds, which could be refined to produce raw industrial materials currently manufactured from petroleum-based sources, pharmaceuticals, surfactants, or food additives as valuable by-products if legume biomass was to be used to generate biodiesel, bioethanol, biojet A1 fuel, or biogas. The attraction of using leguminous material feedstock is that they do not need the inputs of N fertilizer that would otherwise be necessary to support the production of high grain yields or large amounts of plant biomass since it is the high fossil energy use in the synthesis, transport, and application of N fertilizers that often negates much of the net C benefits of many other bioenergy sources. The use of legume biomass for biorefineries needs careful thought as there will be significant trade-offs with the current role of legumes in contributing to the organic fertility of soils. Agricultural systems will require novel management and plant breeding solutions to provide the range of options that will be required to mitigate climate change. Given their array of ecosystem services and their ability to reduce greenhouse gas emissions, lower the use of fossil energy, accelerate rates of C sequestration in soil, and provide a valuable source of feedstock for biorefineries, legumes should be considered as important components in the development of future agroecosystems.