Abstract
Simple SummaryCrops are the primary feedstock for the production of food/feed and energy, and our dependency on them has been increasing over the last decade. Climate change, reduced land for active agriculture, increased population, reduced amount of clean water, and high costs of chemical fertilizers and energy make modern agriculture unsustainable. Demands are rising for the next generation of cheap and sustainable feedstock, which could be productive under existing conditions. Aquatic plants, such as the free-floating species duckweed and Azolla, have started attracting attention because of their unique features, presenting advantages over terrestrial plants. Terrestrial plants grow on the land or need to be on dry land to survive. On the other hand, aquatic plants have the ability to thrive in ponds under controlled conditions using wastewaters as a source of nutrients. Over the last decade, Azolla species became an attractive feedstock for livestock because of their accumulation of valuable products, phenolic compounds, proteins, lipids, and carbohydrates. Stress-triggered changes in these nutritional components could have a significant impact on the nutritional value of Azolla, which is used as a sustainable food supplement for livestock, poultry, and fish industries. This paper aims to assess the effects of environmental and nutrient stresses on the biosynthesis of valuable metabolites in Azolla.The metabolic plasticity of shikimate and phenylpropanoid pathways redirects carbon flow to different sink products in order to protect sessile plants from environmental stresses. This study assessed the biochemical responses of two Azolla species, A. filiculoides and A. pinnata, to the combined effects of environmental and nutritional stresses experienced while growing outdoors under Australian summer conditions. These stresses triggered a more than 2-fold increase in the production of total phenols and their representatives, anthocyanins (up to 18-fold), flavonoids (up to 4.7-fold), and condensed tannins (up to 2.7-fold), which led to intense red coloration of the leaves. These changes were also associated with an increase in the concentration of carbohydrates and a decrease in concentrations of lipids and total proteins. Changes in lipid biosynthesis did not cause significant changes in concentrations of palmitoleic acid (C16:0), linolenic acid (C18:3), and linoleic acid (C18:2), the fatty acid signatures of Azolla species. However, a reduction in protein production triggered changes in biosynthesis of alanine, arginine, leucine, tyrosine, threonine, valine, and methionine amino acids. Stress-triggered changes in key nutritional components, phenolics, lipids, proteins, and carbohydrates could have a significant impact on the nutritional value of both Azolla species, which are widely used as a sustainable food supplement for livestock, poultry, and fish industries.
Highlights
Crops are the primary feedstock for the production of food/feed and energy, and our dependency on them has increased over the last decade
A. filiculoides and A. pinnata plants growing outdoors under normal and stressed conditions (Material and Methods) were assessed for the concentration of phenolic compounds, total phenols, anthocyanins, flavonoids, and condensed tannins, which have a complex effect on the nutritional value of these plants [10,11]
Stress increased the accumulation of phenols up to 2.6-fold in A. pinnata, and 2-fold in A. filiculoides, producing 139.5 mg/g DW (14.2% DW)
Summary
Crops are the primary feedstock for the production of food/feed and energy, and our dependency on them has increased over the last decade. Challenges with harvesting under large scale production make their technology expensive [6,7] Aquatic plants, such as the free-floating species duckweed and Azolla, have started attracting attention because of their unique features, which present the advantages of microalgae with easy and cheap harvesting technologies [8,9,10,11,12,13]. Azolla species grow in a symbiotic association with Nostoc (Anabaena) azollae, a nitrogen-fixing cyanobacterium that allows its host plant to grow rapidly in nitrogen-free solutions [14,15,16] The application of this species for wastewater treatment and the production of biomass for food/feed and as feedstock for bioenergy has been broadly investigated [9,13,17,18,19,20]. Azolla species became an attractive feedstock for livestock because of the accumulation of valuable products, such as proteins (up to 400 g/kg DW), lipids (160 g/kg DW), and phenolics comprising antioxidants such as flavonoids, tannins, and anthocyanins (50 g/kg DW in total) [11,13,20,22,23,24]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call