Search

Sustainability assessments have revealed that integration of CO from coal-fired flue gas with microalgae cultivation systems could reduce greenhouse gas emissions. The technical goal of this integration is to utilize exhaust from coal power plants to enhance microalgae cultivation processes by capturing and recycling of carbon dioxide from a more toxic to a less toxic form. However, heavy metals are also introduced along with CO2 to the cultivation system which could contaminate biomass and have deleterious effects on products derived from such systems. The present study aimed at shedding some light on capability of microalgae to sustain their diversity and propagate them under different CO concentrations from coal-fired flue gas. Mixed microalgal culture was grown in nutrient rich medium and heavy metals (Al, Cu, Fe, Mn and Zn)are expected to be introduced from flue gas. Three concentrations (1%, 3% and 5.5%)of CO were evaluated (reference concentrations from flue gas). Comparative studies were carried out by flue gas and control systems in photobioreactors. Under the 3% CO (30% flue gas), the highest fraction of B, Mn and Zn were found to be internalized by the cells (46.8 ±9.45 gL-1, 253.66 ± 40.62 gL-1 and 355.5 ±50.69 gL-1 respectively)during their cultivation period into biomass. Hence, microalgae may offer solution to two major challenges: providing potential biofuel feedstock for energy security and reducing heavy metal pollution to the air.

Novel energy production systems are needed that not only offer reductions in greenhouse gas emissions but also cause fewer overall environmental impacts. How to identify and implement more sustainable biofuel production alternatives, and how to overcome economic challenges for their implementation, is a matter of debate. In this study, the environmental impacts of alternative approaches to biofuel production (i.e., first, second, and third generation biofuels), with a focus on biodiversity and ecosystem services, were contrasted to develop a set of criteria for guiding the identification of sustainable biofuel production alternatives (i.e., those that maximize socioeconomic and environmental benefits), as well as strategies for decreasing the economic barriers that prevent the implementation of more sustainable biofuel production systems. The identification and implementation of sustainable biofuel production alternatives should be based on rigorous assessments that integrate socioeconomic and environmental objectives at local, regional, and global scales. Further development of environmental indicators, standardized environmental assessments, multi-objective case studies, and globally integrated assessments, along with improved estimations of biofuel production at fine spatial scales, can enhance the identification of more sustainable biofuel production systems. In the short term, several governmental mandates and incentives, along with the development of financial and market-based mechanisms and applied research partnerships, can accelerate the implementation of more sustainable biofuel production alternatives. The set of criteria and strategies developed here can guide decision making towards the identification and adoption of sustainable biofuel production systems.

Aluminium hydroxide hydrate membrane technology was recently developed as a novel, simple, and low cost gel-based filtration system. Previous work examined the properties of the gel and showed that it has great potential to be used as separation means for filtration of suspended solids. In this study, the gel was applied to the dewatering of copper mine tailings for the first time. The filtration process efficiency was measured by filtration rate, the turbidity of the supernatant liquid, cake thickness and the final cake moisture content. The filtration performance was also tested against other filter aids typically used in mining operations. It is evident that the application of hydrate gel membrane for filtrating copper tailings is encouraging. It was found that the comparative advantage of the hydrate membrane lies in producing much lower turbidity water than other filter aids. Although the flux rate of the hydrate gel membrane was a little lower than the three filter aids tested, the cake moisture and thickness was comparable. Also, the hydrate gel membrane could be easily spread out against a retaining fabric and worked well at low to no pressure, with optimum flux rates at about 10 psi and acceptable flux rate at zero pressure. This study suggests that hydrate gel membranes can be applied in the mining industry, especially where operating and capital costs are a concern and operators are seeking low turbidity water and/or a cake suitable for stacking or reprocessing. The technology showed great potential to be utilized for filtering thickener underflow tailings.

Strigolactones are an important group of plant hormones. When released from roots, they act as signalling molecules that induce branching of arbuscular mycorrhizal hyphae. However, the extent to which they affect the rhizosphere microbiome is unknown. Filling this knowledge gap is important because the diversity and composition of the root-associated microbiome influence plant fitness. In this study, we hypothesised that strigolactone-producing plants harbour a different community of rhizosphere bacteria and fungi compared to plants whose strigolactone synthesis is impaired. To test this hypothesis, we compared the diversity of rhizosphere bacterial and fungal communities associated with wild-type Arabidopsis thaliana and a mutant impaired in the production of strigolactones due to a disruption of the MORE AXILLARY GROWTH 4 (MAX4) gene. Our results indicate that the plant's ability to produce strigolactone is significantly correlated with changes in the composition (beta diversity) of rhizosphere fungal but not bacterial communities. No differences in alpha diversity (richness and evenness) were observed for either bacterial or fungal communities between the rhizospheres of max4 and wild-type. Epicoccum nigrum, Penicillium, Fibulochlamys chilensis, Herpotrichiellaceae, Mycosphaerella and Mycosphaerellaceae were among the fungal taxa possibly attracted to or mostly influenced by strigolactones given that they were present at higher abundances in the rhizosphere of the wild-type compared to the mutant. Our study provides evidence that rhizosphere fungal diversity are more strongly affected than bacterial diversity by the plant's ability to produce strigolactones.

Phytophthora capsici causes root, crown and fruit rot on many plant species including tomato and other solanaceous species. Plant growth promotion and suppression of P. capsici on tomato were assessed for three soil bacterial isolates, namely Bacillus amyloliquefaciens (UQ154), Bacillus velezensis (UQ156) and Acinetobacter sp. (UQ202). Cultures were applied as seed treatments (pre and post-infection inoculation) plus a soil drench at transplanting. The bacterial isolates significantly promoted growth of seedlings, as measured by root length, total fresh weight, and seedling vigor. We observed a reduction in pathogen load in tomato roots in both treatments using quantitative Polymerase Chain Reaction (qPCR). This work confirms the broad-spectrum activity of these bacterial isolates for our previous findings of biocontrol activity on different plants.

The paper presents a set of methods for user-centred design of autonomous mobility for public transportation in the context of a multi-disciplinary research programme in Singapore, called TUMCREATE. While traffic engineers plan the operation of the new mobility system, the Industrial Designers of TUMCREATE take on the role of designing the autonomous vehicles (AVs) and infrastructure for greater comfort and a positive travel experience for users. Tasks have been identified to promote user acceptance and facilitate the operation of autonomously driven vehicles for public transport. To fulfil these tasks, conventional design methods have been enhanced with Virtual Reality (VR) technology and with simulations developed by the computer scientists of TUMCREATE. Since public transportation is a complex and broad area, it cannot be investigated with a single design method. First results showed that conventional methods that consider the Universal Design principles guarantee the accessibility, usability and understandability of AVs and stations. VR has been identified as a suitable tool for Industrial Designers to evaluate communication concepts between AVs and pedestrians. This confirms that digital tools (i.e. VR) enhance conventional design methods, especially with regard to technologies that are not available on the market yet (e.g. AVs

Microalgae are a commercially viable route for the production of carotenoids. Chlorella sp. BR2 was treated with plant hormones indole‑3‑acetic acid, salicylic acid, abscisic acid and methyl jasmonate and screened for enhanced carotenoid production. Indole‑3‑acetic acid was the only hormone with an inductive effect on carotenoid accumulation. As such, transcriptome-wide changes following auxin treatment were profiled using RNA-Seq and expressed sequences reconstructed with de novo assembly. This revealed the active pathway components of auxin-induced carotenogenesis. Data analysis specified the differentially expressed genes involved in auxin biosynthesis and signal transduction, which hint at close, yet unique relationship to equivalent pathways in higher plants. Unlike in plants, the ancient ABP1/SCFSKP2A/IBR5-mediated pathways for auxin response likely acted as the primary signaling route in Chlorella. As carotenoids are precursors for abscisic acid and antagonists of reactive oxygen species, the findings suggest a potential link between auxin signaling and abiotic stress tolerance.

Haematococcus pluvialis accumulates large amounts of astaxanthin during its haematocyst stage. Cyst germination is a biological pretreatment method for improved astaxanthin extraction with potential to replace energy-intensive homogenizer-based mechanical cell cracking methods. The present study demonstrates effects of different LED light wavelengths on haematocyst germination and on its astaxanthin biosynthesis pathway. Blue light enhanced the germination efficiency and slowed the nitrogen consumption rate, resulting in significantly higher astaxanthin content and improved extractability compared with white and red lights, that also had lower germination rates. After 5 days, the total astaxanthin extractability under blue light was 4.0 and 6.7 times higher than for white and red lights, respectively. The blue light receptor gene phot was significantly induced which upregulated the biosynthesis pathway genes psy and pds, as well as dgat1 and dgat2d. Hence, blue light triggers germination and astaxanthin biosynthesis, providing a strategy for improved extraction while modulating higher biosynthesis during germination.

Microalgae in the Middle East can theoretically address food security without competing for arable land, but concerns exist around scalability and durability of production systems under the extreme heat. Large-scale Chlorella sorokiniana production was developed in outdoor raceway ponds in Oman and monitored for 2 years to gather data for commercial production. Biological and technical challenges included construction, indoor/outdoor preculturing, upscaling, relating productivity to water temperature and meteorological conditions, harvesting, drying, and quality control. Small cultivation systems required cooling for initial scale-up, but, despite maximum temperatures of 49.7 °C, water temperatures were at acceptable levels by evaporative cooling in larger raceway ponds. Contamination with Vampirovibrio chlorellavorus was identified by 16S rDNA amplicon sequencing and addressed by culture replacement. Productivities ranged from 8 to 30 g-dry weight m-2d-1, with estimated annual productivity of 16 g-dry weight m-2d-1 as functions of solar intensity and water temperature, confirming that the region is suitable for commercial microalgae production.

Salicylic acid (SA) plays an important role in plant defence against biotrophic pathogens. Recent work with Arabidopsis thaliana mutants indicates an association between SA signalling and the diversity of root-associated microbial communities. This has led to the idea that activation of the SA pathway may help plants to rapidly recruit microbes that enhance stress tolerance and could be exploited as an approach to engineer beneficial plant microbiomes in agriculture. Nonetheless, unlike plants in natural environments, mutants with altered SA signalling constitutively express their phenotype. For this reason, we investigated whether transient activation of the SA pathway in wheat (Triticum aestivum) leads to rapid changes in the composition of root microbiomes. High throughput phylogenetic marker gene sequencing demonstrated that, 72 h post-treatment, SA had no significant effects on the richness, evenness and composition of bulk soil and root-associated microbiomes in two soil types. These findings indicate that the structure of wheat root-associated microbiomes did not undergo significant rapid changes in response to activation of the SA signalling pathway.

The microalga Nannochloropsis produces high-value omega-3-rich fatty acids and carotenoids. In this study the effects of light intensity and wavelength on biomass, fatty acid, and carotenoid production with respect to light output efficiency were investigated. Similar biomass and fatty acid yields were obtained at high light intensity (150 μmol m-2 s-1) LEDs on day 7 and low light intensity (50 μmol m-2 s-1) LEDs on day 11 during cultivation, but the power efficiencies of biomass and fatty acid (specifically eicosapentaenoic acid) production were higher for low light intensity. Interestingly, low light intensity enhanced both, carotenoid power efficiency of carotenoid biosynthesis and yield. White LEDs were neither advantageous for biomass and fatty acid yields, nor the power efficiency of biomass, fatty acid, and carotenoid production. Noticeably, red LED resulted in the highest biomass and fatty acid power efficiency, suggesting that LEDs can be fine-tuned to grow Nannochloropsis algae more energy-efficiently.

The sustainable, efficient production of biofuel can lead to reductions in greenhouse gas emissions, lowered climate change impact and increased security owing to the fulfilment of global energy demands. Microalgae have been shown as an attractive feedstock for renewable fuel production, such as biodiesel and biogas. To date, more effort has been put towards the production of biodiesel using the lipid contents in algal cells, while less attention has been placed on biogas production through anaerobic digestion. However, anaerobic digestion has the potential to generate energy from waste residues and to mobilize nutrients enabling subsequent recovery and/or recycling. Therefore, anaerobic digestion is an area with strong potential for novel research focusing on the development of a sustainable integrated system of biodiesel and biogas production. The result is essentially a solar power plant, producing fuel with minimal inputs and a closed nutrient loop, a necessity for sustainable and cost-efficient production of biofuel. In this review we discuss relevant studies on biodiesel and biomethane production, including the potential improvements and advantages when using an integrated approach for biodiesel and biogas production with special focus on nutrient recycling.

Biodiesel is produced by transesterification of fatty acid methyl esters (FAME) from oleaginous microalgae feedstock. Biodiesel fuel properties were studied and compared with biodiesel standards. Qualitative analysis of FAME was done while cultivating mixed microalgae consortia under three concentrations of coal fired flue gas (1%, 3.0% and 5.5% CO2). Under 1% CO2 concentration (flue gas), the FAME content was 280.3 μg/mL, whereas the lipid content was 14.03 μg/mL/D (day). Both FAMEs and lipid contents were low at other CO2 concentrations (3.0 and 5.5%). However, mixed consortia in the presence of phosphate buffer and flue gas (PB + FG) showed higher saturated fatty acids (SFA) (36.28%) and unsaturated fatty acids (UFA) (63.72%) versus 5.5% CO2 concentration, which might be responsible for oxidative stability of biodiesel. Subsequently, higher cetane number (52) and low iodine value (136.3 gI2/100 g) biodiesel produced from mixed consortia (PB + FG) under 5.5% CO2 along with 50 mM phosphate buffer were found in accordance with European (EN 14214) standard. Results revealed that phosphate buffer significantly enhanced the biodiesel quality, but reduced the FAME yield. This study intended to develop an integrated approach for significant improvement in biodiesel quality under surplus phosphorus by utilizing waste flue gas (as CO2 source) using microalgae. The CO2 sequestration from industrial flue gas not only reduced greenhouse gases, but may also ensure the sustainable and eco-benign production of biodiesel.

Phaeodactylum tricornutum is a genetically well-studied microalga but commercial production of omega-3 fatty acids and protein had not been established. Here, a biorefinery platform to cost-effectively culture, harvest and process this diatom has been developed. Using a sea salt substitute supplemented with magnesium enabled low-cost land-based cultivation, reaching biomass yields of 0.17 g L−1day−1 and 340 g m−2day−1 in free-standing outdoor photobioreactors. pH-induced auto-flocculation in bioreactors or open ponds followed by solar drying was most cost-effective to harvest dry biomass. Lipids extracted by organic solvents accounted for 27.3% per dry biomass. Ethanol was the safest and most suitable option for a biorefinery yielding 92% of extractable omega-3 eicosapentaenoic acid (EPA) and 40.9% of protein in the defatted biomass. Using Central Composite Design, optimized alkaline extraction recovered 60.4% of total protein. A cost comparison to Nannochloropsis microalgae showed that EPA-rich oil and protein for human consumption are the most viable products with potentially lower EPA production costs. This study demonstrates that land-based P. tricornutum cultivation can provide a sustainable source of omega-3 fatty acid without putting pressures on marine bioresources.

Implementing intercropping and applying arbuscular mycorrhizal (AM) fungi can be alternatives for applying chemical fertilizers. We investigated the effectiveness of Glomus intraradices on yield, land equivalent ratio (LER), yield of essential oil (EO) and EO composition of coriander (Coriandrum sativum L.) in different cropping systems. Two experiments were carried out in triplicate with a complete, randomized block design in the years 2017 and 2018. The cropping systems included a) coriander sole cropping at 25, 50 or 75 plants m−2, b) soybean (Glycine max L.) sole cropping at 40 plants m−2, and c) intercropping of different densities of coriander (25, 50 or 75 plants m−2) with soybean at 40 plants m−2. All cropping systems were exposed to treatments without (-AM) or with (+AM) application of Glomus intraradices. Applying G. intraradices significantly increased contents of macro- and micronutrients in coriander plants, and also enhanced LER and EO yield. Implementing intercropping and applying AM inoculation affected EO composition in coriander. The contents of limonene, apiole, coriander ether, n-dihydrocarvone, carvone, myristicin and coriander_apiole was enhanced in AM treated and intercropped coriander plants, while applying G. intraradices resulted in a reduced content of cis-sabinol and phytol of sole-cropped and intercropped coriander plants.

Energy and fuel demands, which are currently met primarily using fossil fuels, are expected to increase substantially in the coming decades. Burning fossil fuels results in the increase of net atmospheric CO2 and climate change, hence there is widespread interest in identifying sustainable alternative fuel sources. Biofuels are one such alternative involving the production of biodiesel and bioethanol from plants. However, the environmental impacts of biofuels are not well understood. First generation biofuels (i.e. those derived from edible biomass including crops such as maize and sugarcane) require extensive agricultural areas to produce sufficient quantities to replace fossil fuels, resulting in competition with food production, increased land clearing and pollution associated with agricultural production and harvesting. Microalgal production systems are a promising alternative that suffer from fewer environmental impacts. Here, we evaluate the potential impacts of microalgal production systems on biodiversity compared to first generation biofuels, through a review of studies and a comparison of environmental pressures that directly or indirectly impact biodiversity. We also compare the cultivation area required to meet gasoline and distillate fuel oil demands globally, accounting for spatial variation in productivity and energy consumption. We conclude that microalgal systems exert fewer pressures on biodiversity per unit of fuel generated compared to first generation biofuels, mainly because of reductions in direct and indirect land-use change, water consumption if water is recycled, and no application of pesticides. Further improvements of technologies and production methods, including optimization of productivities per unit area, colocation with wastewater systems and industrial CO2 sources, nutrient and water recycling and use of coproducts for internal energy generation, would further increase CO2 savings. Overall pollution reductions can be achieved through increased energy efficiencies, along with nutrient and water recycling. Microalgal systems provide strong potential for helping in meeting global energy demands sustainably.

The plant holobiont - which is the plant and its associated microbiome - is increasingly viewed as an evolving entity. Some interacting microbes that compose the microbiome assist plants in combating pathogens and herbivorous insects. However, knowledge of the factors that influence the microbiome in the context of defence signalling pathways is still in its infancy. Recent research reported that changes in jasmonic acid (JA) and salicylic acid signalling affects the root microbiome of Arabidopsis thaliana. This review aims to present the hypothesis that the JA pathway represents a novel mechanism for microbiome engineering for improved holobiont fitness in agricultural systems.

An integrated system for biodiesel and biogas production for the diatom Chaetoceros muelleri was evaluated. We assessed the suitability of osmotic shock pre-treatment of wet microalgal biomass for lipid extraction and biogas production. Osmotic shock pre-treatment released up to 72% of C. muelleri lipid content. Biogas production of pre-treated and lipid-spent microalgae was evaluated by biomethane potential tests and by operating two continuous anaerobic reactors for 200 days. An improvement of 35% in methane production was observed with the pre-treated microalgae in batch conditions, with a maximum methane yield of 521 mL CH4 g VS−1. The methane yield in the continuous experiments of the pre-treated microalgae fluctuated between 0.3 and 0.7 L CH4 g VS−1, with an average of 0.52 L CH4 g VS−1. No significant differences were observed between the pre-treated microalgae without lipid extraction and lipid-spent microalgae in both batch and continuous conditions. The energy potential for a combined biodiesel-biogas biorefinery has been estimated at 20.5 KJ gVS−1 of harvested microalgae.

The effects of arbuscular mycorrhiza fungi (AMF) species (Glomus intraradices and G. mosseae), nitrogen (N) fertilizer and plant growth-promoting rhizobacteria (PGPR) on growth characteristics, essential oil (EO) content, nutrient uptake and components of medicinal plants basil (Ocimum basilicum) and satureja (Satureja hortensis) were studied. The use of these fertilizers significantly (P < 0.05) increased plant height, root length, fresh and dry weights of shoots and roots, number of shoot branches and number of inflorescences per plant, EO content, phosphorus (P), nitrogen (N), iron (Fe), potassium (K), and copper (Cu) content. Moreover, application of AMF and PGPR significantly (P < 0.05) enhanced linalol, methyl chavicol, trans-geraniol, camphor and limonene concentrations in basil EO and carvacrol, thymol, p-cymene, α-terpinene and γ-terpinene in satureja EO components. G. mosseae application achieved the highest increases in basil and satureja EO percentage by 39 % and 25 %, respectively, compared to plants treated with mineral fertilizer, and 80 % and 50 %, respectively, compared to unfertilized plants. The highest N, K, Fe and P concentrations in basil and satureja were obtained when PGPR or G. mosseae were used. This study shows that application of biofertilizers not only improves yields in medicinal plants, but they also play a significant role in increasing their bioactive compounds and plant nutrition.

Microalgae are a promising alternative for future biofuel production. Compared to first- and second-generation biofuels, microalgal production systems offer higher biofuel productivities per unit area and do not necessarily depend on fertile soils or freshwater. However, little is known about how microalgal biofuel production on a scale large enough to meet a nation’s domestic transport energy targets might conflict with agricultural lands and biodiversity in the context of energy independence. Here, we use estimates of lipid productivity, resource availability, and accessibility to identify the most cost-effective areas for fulfilling 30% of each country’s transport energy demands in 2016 and 2050 while avoiding areas of high agricultural and biodiversity value. To fulfill this target, microalgal cultivation would need less than 1.1% of global land area, mainly in drier low-latitude areas or drier lowlands within each country. The most promising countries for microalgal biofuel production are mainly located in North and East Africa, the Middle East, western South America, the Caribbean, and Oceania. In countries with either high energy demands or without available human-transformed dry lands, decreasing targets in microalgal biofuel production or shifting production to countries where impacts are lower, could further reduce potential conflicts with food production and biodiversity.

High-yielding microalgae present an important commodity to sustainably satisfy burgeoning food, feed and biofuel demands. Because algae-associated bacteria can significantly enhance or reduce yields, we isolated, identified and selected highly-effective “probiotic” bacterial strains associated with Nannochloropsis oceanica, a high-yielding microalga rich in eicosapentaenoic acid (EPA). Xenic algae growth was significantly enhanced by co-cultivation with ten isolated bacteria that improved culture density and biomass by 2.2- and 1.56-fold, respectively (1.39 × 108 cells mL−1; 0.82 g L−1). EPA contents increased up to 2.25-fold (to 39.68% of total fatty acids). Added probiotic bacteria possessed multiple growth-stimulating characteristics, including atmospheric nitrogen fixation, growth hormone production and phosphorous solubilization. Core N. oceanica-dominant bacterial microbiomes at different cultivation scales included Sphingobacteria, Flavobacteria (Bacteroidetes), and α, γ-Proteobacteria, and added probiotic bacteria could be maintained. We conclude that the supplementation with probiotic algae-associated bacteria can significantly enhance biomass and EPA production of N. oceanica.

Solvent-free microalgal lipid recovery is highly desirable for safer, more sustainable and more economical microalgal oil production. Dispersed air flotation and centrifugation were evaluated for the ability to separate oil and debris from a slurry mixture of osmotically fractured Chaetoceros muelleri cells with and without utilizing collectors. Microalgal oil partially phase-separated as a top layer and partially formed an oil-in-water emulsion. Although collectors, such as sodium dodecyl sulphate enhanced selective flotation, by just adjusting the pH and cell concentration of the mixture, up to 78% of the lipids were recovered in the froth. Using centrifugation of fractured microalgal slurry resulted in removal of 60% cell debris and up to 68.5% of microalgal oil was present in the supernatant. Both methods, centrifugation and flotation provided options for separation of microalgal oil from C. muelleri slurry with similar fatty acid recoveries of 57% and 60%, respectively.

Strategic tillage (or occasional tillage) has been touted as a potential solution for the severe weed infestations of long-term no-till (NT). Nevertheless, there is little information on the influence of strategic tillage on microbial properties of Australian NT soils. In the present study, we assessed the influence of strategic tillage on the microbial properties of a seven years’ NT Calcisol in Moonie, Queensland, Australia. We tested the hypothesis that the application of one-time strategic tillage with chisel or offset disc does not cause major impacts on soil biological health in a NT system. Strategic tillage was applied once and soil samples were collected 13 months after tillage from the depths 0–10 and 10–20 cm. The measured biological indicators included soil microbial biomass carbon, catabolic activity (MicroResp™ assay) and total microbial activity (fluorescein diacetate method). The structure of bacterial communities was profiled by quantitative polymerase chain reaction (qPCR) and terminal reaction fragment length polymorphism (T-RFLP). Principal components analyses based on qPCR and T-RFLP data did not show tillage effects on soil bacterial communities. However, relative to the NT, chisel tillage led to significant increases in microbial biomass carbon (+34.4%), abundances of Alphaproteobacteria (+74.6%), Bacteroidetes (+113.7%) and Firmicutes (+36.5%), and the utilisation of D+ cellubiose (+178.4%) as well as mannitol (+167.2%) at 0–10 cm depth. In contrast, the influence of offset disc tillage was restricted to an increased abundance of Alphaproteobacteria (+64.6%) at 0–10 cm depth. Our study suggests that, overall, one-time strategic tillage using either chisel or offset disc had a minor positive influence on soil biological attributes of the NT Calcisol 13 months after tillage.

Occasional strategic tillage (ST) has been suggested as a possible solution to manage herbicide-resistant weeds and control crop diseases in Australia's northern grain-growing regions. We evaluated the impact of ST on microbial communities as indicators of soil quality for two distinct tillage systems that have been applied to a Vertosol for 43 years (no-tillage – NT or conventional tillage – CT) and two stubble management practices (retention – SR or burning – SB). Soil samples were collected 15 weeks after ST and analysed for total enzymatic activity (fluorescein diacetate assay), metabolic diversity (Ecoplates Biolog®) and bacterial community structure (terminal restriction fragment length polymorphism). There was no significant effect of ST on the measured biological attributes. However, total enzymatic activity for treatments under CTSR and CTSR-ST were significantly higher compared with NTSR-ST (+0.8 fluorescein μg ml−1 g−1 soil h−1, P < 0.01). Differences may be attributed to a significant increase in bulk density for CTSR treatment (P < 0.05) and an increment in bulk density on CTSR-ST plots. The lack of changes may be attributed to a high resistance and/or resilience of soil microbial communities after 15 weeks of tillage. More studies on the long-term effect of ST are required to assess the impact on soil biological properties.

Over half of the arable land in the northern grains region of Australia is managed using no-till (NT), a farming method which has improved crop yields and soil quality while reducing the input and labour costs. However, concerns have arisen among farmers over the control of weeds in continuous NT systems. An occasional targeted tillage operation (termed strategic tillage — ST) has been proposed as a management tool to reduce problem weed populations but may adversely influence soil properties and those of associated microbial communities. To assess the potential impacts of a ST operation on soil properties, a Grey Vertosol with fifteen years of NT in Northern New South Wales, Australia was tilled using either a chisel cultivator or disc chain on March 15th 2013 or on April 5th 2013. We hypothesised that ST using these minimal or low soil inversion implements at either timing would not adversely influence soil properties in the short-term (4–7 weeks). The measured soil properties were soil volumetric moisture content (VMC), pH, bulk density (BD), electrical conductivity (EC), available phosphorus (P), soil organic carbon (SOC), microbial biomass carbon (MBC), metabolic activity (MA), genetic structures of bacterial communities and wheat yield (t ha− 1). We found that ST with either a chisel cultivator or a disc chain has great potential to assist in weed management as it did not statistically influence crop productivity or the physical, chemical and biological properties of the soil, regardless of the tillage timing.

Harvesting of oleaginous marine microalgae by dewatering is an important step for cost-effective algal biomass feedstock production. This paper reports separation of marine microalgae (Tetraselmis sp. M8) from aqueous medium by froth flotation using various collectors (surfactants) with equal carbon chain length, such as dodecyl pyridinium chloride (DPC), N-dodecylpropane-1,3-diamine hydrochloride (DN2), dodecyl amine hydrochloride (DAH), and sodium dodecyl sulphate (SDS), at different pHs. Algal hydrophobicity, froth stability, and surfactant precipitation were characterised. The laboratory-scale mechanical flotation tests showed that at natural pH 9.5 and a lower pH, DPC outperformed DAH, DN2 and SDS in separating Tetraselmis sp. M8 from seawater. DPC was capable of rendering the microalgae hydrophobic, producing metastable froth, and dissolving readily in water, which are all desirable features of a collector for flotation separation of microalgae from water. Use of DPC at 15 ppm in pilot-scale Jameson cell flotation tests for M8 after outdoor cultivation led to a 23-fold increase in algal concentration with over 99% algal recovery. (C) 2015 Elsevier B.V. All rights reserved.

Nannochloropsis is one of the most-studied microalgae because of its high eicosapentaenoic acid (EPA) content and high-value carotenoids. However, during large-scale farming, decreased EPA productivity of Nannochloropsis oceanica BR2 was observed when cultured during the summer season (≥30 °C). We hypothesized that short low temperature treatments and membrane biosynthesis during reduced light exposure may increase EPA yields. Thus, we investigated the effect of 3-day cold or dark treatments on N. oceanica BR2 nutritional composition by measuring fatty acid and carotenoid profiles. Indeed, treated samples contained increased levels of polyunsaturated fatty acids including EPA and carotenoids violaxanthin and zeaxanthin. Tunnelling electron microscopy showed increased an chloroplast size and an increased number of thylakoid membranes in treated samples, visualizing how cells adapt to these environmental changes. The present study provides a practical strategy on how heat-stressed Nannochloropsis cultures can be subjected to short 3-day treatments before harvesting to enable high-value biomass production.