Age versus stage: does ontogeny modify the effect of phosphorus and arbuscular mycorrhizas on above- and below-ground defence in forage sorghum?

Article first published online: 11 NOV 2013Arbuscular mycorrhizas (AM) can increase plant acquisition of P and N. No published studies have investigated the impact of P and AM on the allocation of N to the plant defence, cyanogenic glucosides. We investigated the effects of soil P and AM on cyanogenic glucoside (dhurrin) concentration in roots and shoots of two forage sorghum lines differing in cyanogenic potential (HCNp). Two harvest times allowed plants grown at high and low P to be compared at the same age and the same size, to take account of known ontogenetic changes in shoot HCNp. P responses were dependent on ontogeny and tissue type. At the same age, P-limited plants were smaller and had higher shoot HCNp but lower root HCNp. Ontogenetically controlled comparisons showed a P effect of lesser magnitude, and that there was also an increase in the allocation of N to dhurrin in shoots of P-limited plants. Colonization by AM had little effect on shoot HCNp, but increased root HCNp and the allocation of N to dhurrin in roots. Divergent responses of roots and shoots to P, AM and with ontogeny demonstrate the importance of broadening the predominantly foliar focus of plant defence studies/theory, and of ontogenetically controlled comparisons.Rebecca E. Miller, Roslyn M. Gleadow and Timothy R. Cavagnar

Drought adversely affects tuber development and nutritional quality of the staple crop cassava (Manihot esculenta Crantz)

Cassava (Manihot esculenta Crantz) is the staple food source for over 850 million people worldwide. Cassava contains cyanogenic glucosides and can be toxic to humans, causing paralysing diseases such as konzo, and even death if not properly processed. Konzo epidemics are often associated with times of drought. This may be due to a greater reliance on cassava as it is drought tolerant, but it may also be due to an increase in cyanogenic glucosides. Episodic droughts are forecast to become more common in many cassava-growing regions. We therefore sought to quantify the effect of water-stress on both yield and cyanogenic glucoside concentration (CNc) in the developing tubers of cassava. Five-month-old plants were grown in a glasshouse and either well watered or droughted for 28 days. A subset of droughted plants was re-watered half way through the experiment. Droughted plants had 45% fewer leaves and lower tuber yield, by 83%, compared with well-watered plants. CNc was 2.9-fold higher in the young leaves of droughted plants, whereas CNc in tubers from droughted plants was 4-fold greater than in tubers from well-watered plants. Re-watered plants had a similar biomass to control plants, and lower CNc than droughted plants. These findings highlight the important link between food quality and episodic drought.Rebecca Vandegeer, Rebecca E. Miller, Melissa Bain, Roslyn M. Gleadow and Timothy R. Cavagnar

Organic amendments as phosphorus fertilisers: chemical analyses, biological processes and plant P uptake

As phosphorus (P) fertilisers become increasingly expensive there is a need to find innovative ways to supply crops with P. Organic amendments (OA) can contain high concentrations of total P, although the P is present in various forms. We aimed to determine the forms of P and carbon (C) in a range of OA and the effect of these OA on soil microbial biomass, P release, arbuscular mycorrhizal (AM) colonisation, and plant P uptake. Four OA were investigated: two chicken litters (CHK-STR and CHK-SD, one with straw bedding and one with sawdust bedding), a pig litter (PIG-STR) and a municipal waste compost (COMP). An incubation experiment and a plant growth experiment were conducted in which OA and INORG-P were supplied at 15 mg P kg−1 soil and a zero P control was included. All OA had high P concentrations and did not result in an increase in the soil microbial biomass C. There were few temporal changes in available P throughout the incubation experiment suggesting that solubilisation and/or mineralisation of P occurred at a similar rate as conversion of P to unusable forms. Of the OA, PIG-STR had the largest proportion of orthophosphate P and bicarbonate extractable P, and it provided the most P to plants. While CHK-STR had a higher proportion of orthophosphate P and bicarbonate extractable P than CHK-SD, both CHK-STR and CHK-SD provided plants with similar amounts of P. This could be because CHK-SD had a higher proportion of phytate, which can be rapidly mineralised to orthophosphate, and/or because plants in the CHK-SD had higher rates of arbuscular mycorrhizal (AM) colonisation compared with CHK-STR. This study provides new insights into plant and microbial responses to OA which could help in the development of sustainable food production systems.J.E. Mackay, L.M. Macdonald, R.J. Smernik, T.R. Cavagnar

Assessing changes in structural vegetation and soil properties following riparian restoration

Efforts are underway in many areas to restore riparian zones to arrest and/or reverse their degradation and the subsequent loss of the ecosystem services they provide. Despite strong links between edaphic conditions and riparian zone function, limited research has tested how soil properties respond to restoration, especially in an experimental context. With this important knowledge gap in mind, we established a field experiment to asssess structural vegetation and soil responses in the eight years following livestock exclusion and replanting in lowland streams in south-eastern Australia. On three streams, paired restored and control sites were experimentally established and we monitored vegetation (stem density, cover of bare ground and tree canopy, and loadings of organic matter), once beforehand, and then biennually after restoration. Selected soil properties (total carbon, total nitrogen, plant-available phosphorus) were sampled once shortly after restoration, then after another five years. Significant changes in structural vegetation occurred (e.g. decreased bare ground, increased plant stem density, organic matter, and canopy cover). In contrast, those soil properties did not respond. A mega-drought occurred throughout much of the study which was immediately followed by severe flooding. The floods redistributed organic matter at our study sites, with this effect mediated by vegetation structure: the probability of organic matter retention was positively correlated with groundcover and stem density of plants. The timing of flooding was also correlated with increased soil carbon and nitrogen, which could be due to increased productivity in these systems (for the former), or potentially due to increased fertiliser inputs or increased fixation (for the latter). Our study is the first to comprehensively and experimentally test how vegetation, litter layer and surface soil properties respond following riparian restoration, and will help guide the development and implementation of other monitoring programmes.Robin Hale, Paul Reich, Tom Daniel, Philip S. Lake, Timothy R. Cavagnar

Scales that matter: guiding effective monitoring of soil properties in restored riparian zones

Considerable effort has been directed at restoring riparian zones to ensure they continue to provide ecosystem services and one of the most common aims of these activities is to reduce nutrients (in either water or soil) entering waterways. Vegetation plays a major role in nutrient interception, but nutrients in terrestrial ecosystems are strongly influenced by edaphic factors. Therefore understanding the effectiveness of riparian restoration efforts is dependent on knowledge of the complex and highly dynamic nature of nutrient cycling processes in riparian soils and their adjacent landscapes. Our primary aim was to assess the potential utility of a range of common soil indicators for monitoring responses to riparian restoration, and to use this information to provide guidance for more effective monitoring. A range of soil physiochemical properties in riparian zones and adjacent paddocks as a comparison were measured, incorporating both structural (e.g., bulk density) and functional (e.g., nitrogen) variables likely to differ in terms of both their responsiveness to restoration, and degree of natural spatial and temporal variation. Soil properties across the three spatial scales considered here (among creeks, among sites and within sites) varied considerably, particularly levels of phosphorus, ammonium and nitrate. Total organic carbon and total nitrogen were less variable and more uniform across all scales. Potential explanations for these patterns were explored by examining relationships between soil properties and vegetation measures, and between a subset of the most promising indicators (carbon, total nitrogen and bulk density, based on inherently low spatial variability) and adjacent land-use. Fertiliser inputs appear to be a strong determinant of soil phosphorus but otherwise soil properties were not strongly related to vegetation or adjacent land-use. For mineral N this is likely a reflection of the highly spatiotemporally dynamic nature of nutrient cycling in riparian zone soils. A better understanding of natural variability in soil properties will greatly aid in developing more effective monitoring programmes to assess potential changes in riparian soil properties. Management of riparian systems to recover soil ecosystem services will depend upon identifying effective ecological indicators that can be used as measures of progress towards restoration goals. This study represents a necessary first step towards guiding meaningful monitoring of soil properties at riparian zones subject to restoration efforts.Robin Hale, Paul Reicha, Tom Daniel, Philip S. Lake, Timothy R. Cavagnar

Enhancement of sorghum grain yield and nutrition: A role for arbuscular mycorrhizal fungi regardless of soil phosphorus availability

Societal Impact Statement Sorghum is an important cereal crop that provides calories and nutrients for much of the world's population, and it is often grown with low fertiliser input. Optimising the yield, nutritive content and bioavailability of sorghum grain with minimal input is of importance for human nutrition, and arbuscular mycorrhizal (AM) fungi have previously shown potential to assist in this. Across sorghum genetic diversity, AM fungi improved the yield, nutrition and zinc and iron bioavailability of grain in a low phosphorus soil. Thus, food production systems that effectively manage AM fungi may improve consumer outcomes. Summary Sorghum is a C4 cereal crop that is an important source of calories and nutrition across the world, predominantly cultivated and consumed in low- and middle-income countries. Sorghum can be highly colonised by arbuscular mycorrhizal (AM) fungi, and the plant-fungal association can lead to improvements in biomass and nutrient uptake. High-throughput phenotyping allows us to non-destructively interrogate the ‘hidden’ effects of AM fungi on sorghum growth and phenology. Eight genetically diverse sorghum genotypes were grown in a soil amended with 2 or 20 mg P kg−1 and inoculated with an AM fungal culture of Rhizophagus irregularis. High-throughput phenotyping uncovered the ‘hidden’ effects of AM fungi on growth and phenology, while grain biomass, nutrition, Zn and Fe bioavailability and root AM colonisation was determined after destructive harvest. Sorghum plants colonised by AM fungi generally performed better than non-AM control plants, with greater yield, harvest indices, and grain P, Zn and Fe contents. During the early growth stages, AM colonisation led to temporary growth depressions. There were also AM fungal and P fertilisation effects on sorghum time-of-flowering. The sorghum genotype with the highest AM colonisation could barely produce grain when non-inoculated. The two genotypes that failed to mature had very low AM colonisation. Generally, the genetically diverse sorghum genotypes were highly responsive to AM colonisation and produced more grain of greater nutritive quality when colonised, without adverse consequences for micronutrient bioavailability

Do organic inputs alter resistance and resilience of soil microbial community to drying?

Abstract not availableE.-L. Ng, A.F. Patti, M.T. Rose, C.R. Schefe, R.J. Smernik, T.R. Cavagnar

Does the chemical nature of soil carbon drive the structure and functioning of soil microbial communities?

Abstract not availableE.-L. Ng, A.F. Patti, M.T. Rose, C.R. Schefe, K. Wilkinson, R.J. Smernik, T.R.Cavagnar

A slow release nitrogen fertiliser produced by simultaneous granulation and superheated steam drying of urea with brown coal

Background: The inefficient use of nitrogen (N) fertiliser as a consequence of N losses from soil is a pressing issue in broad-acre agricultural systems. The research reported here tested the hypothesis that granulation of synthetic N fertiliser (urea) with a natural organic C resource (brown coal) would reduce fertiliser N loss from the soil system. Results: Urea-enriched brown coal granules were simultaneously formed and dried within a pilot-scale superheated steam dryer. After application to unplanted soil columns, the urea-brown coal granules reduced nitrous oxide emission by up to 40 %, reduced mineral nitrogen leaching and maintained higher levels of N in topsoil when compared to conventional urea alone. Reduced gaseous N losses without a reduction in plant N uptake were also observed in planted soil columns treated with urea-brown coal granules. Conclusions: Brown coal-urea blended fertiliser showed potential for more efficient use of N in the long term and has environmental benefits in retaining more N in the soil

An ontology for strongly sustainable business models: Defining an enterprise framework compatible with natural and social science

Business is increasingly employing sustainability practices, aiming to improve environmental and social responsibility while maintaining and improving profitability. For many organizations, profit-oriented business models are a major constraint impeding progress in sustainability. A formally defined ontology, a model definition, for profit-oriented business models has been employed globally for several years. However, no equivalent ontology is available in research or practice that enables the description of strongly sustainable business models, as validated by ecological economics and derived from natural, social, and system sciences. We present a framework of strongly sustainable business model propositions and principles as findings from a transdisciplinary review of the literature. A comparative analysis was performed between the framework and the Osterwalder profit-oriented ontology for business models. We introduce an ontology that enables the description of successful strongly sustainable business models that resolves weaknesses and includes functionally necessary relationships