Growing Azolla to produce sustainable protein feed: the effect of differing species and CO₂ concentrations on biomass productivity and chemical composition

Abstract

BACKGROUNDSince available arable land is limited and nitrogen fertilizers pollute the environment, cropping systems ought to be developed that do not rely on them. Here we investigate the rapidly growing, N2‐fixing Azolla/Nostoc symbiosis for its potential productivity and chemical composition to determine its potential as protein feed.RESULTSIn a small production system, cultures of Azolla pinnata and Azolla filiculoides were continuously harvested for over 100 days, yielding an average productivity of 90.0–97.2 kg dry weight (DW) ha−1 d−1. Under ambient CO2 levels, N2 fixation by the fern's cyanobacterial symbionts accounted for all nitrogen in the biomass. Proteins made up 176–208 g kg−1 DW (4.9 × total nitrogen), depending on species and CO2 treatment, and contained more essential amino acids than protein from soybean. Elevated atmospheric CO2 concentrations (800 ppm) significantly boosted biomass production by 36–47%, without decreasing protein content. Choice of species and CO2 concentrations further affected the biomass content of lipids (79–100 g kg−1 DW) and (poly)phenols (21–69 g kg−1 DW).CONCLUSIONSBy continuous harvesting, high protein yields can be obtained from Azolla cultures, without the need for nitrogen fertilization. High levels of (poly)phenols likely contribute to limitations in the inclusion rate of Azolla in animal diets and need further investigation. © 2018 The Authors. Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Differential Production of Phenolics, Lipids, Carbohydrates and Proteins in Stressed and Unstressed Aquatic Plants, Azolla filiculoides and Azolla pinnata

“…However, 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 ].…”

“…Azolla thrives in tropical to temperate regions of the world [ 15 , 21 ]. When grown under optimal conditions, this species can double its biomass every two to four days, with average annual productivity of 39 t/hectare [ 11 ]. Over the last decade, 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 ].…”

“…Azolla’s protein level and composition of amino acids are the main nutritional components that make it a valuable feed supplement [ 11 , 29 , 30 ]. An average yield of dry Azolla biomass of 35 t DW/ha-year correlates with an annual protein production of 7–9 t DW/ha-year [ 29 ].…”

Morphological and Molecular Phylogenetic Analyses Reveal a New Record to the Flora of Iraq: Azolla filiculoides

“…It could be useful by providing ecological benefits to the river. For example, this species is a good nitrogen fixer and it can purify the water from heavy metals (Brouwer et al, 2018). In addition, it could be a good replacer of protein for fishes (Mosha, 2018).…”

An Exploration of Common Greenhouse Gas Emissions by the Cyanobiont of the Azolla–Nostoc Symbiosis and Clues as to Nod Factors in Cyanobacteria

“…At an ambient CO 2 concentration of 800 ppm, Azolla spp., in a small-scale production system, showed a strong increase in biomass production, i.e., 36-47%, which establishes the potential of Azolla spp. as a solution to elevated atmospheric carbon dioxide levels [8]. Azolla spp.…”