Algae biostimulants: A critical look at microalgal biostimulants for sustainable agricultural practices

Humus Acids in the Digested Sludge and Their Properties

Fulvic acids, alpha (α) humic acids and hymatomelanic acids were extracted digested sludge in two Cracow sewage treatment plants: Kujawy and Płaszów. Their elemental composition was examined and micropollution and ash content were determined. Based on the IR and UV-VIS spectrum, their similarities were determined with the occurring interactions with micropollution. Strong correlations between the acids coming from different sources depend on acid type and micropollution accompanying them, depending on concentration, influences to a specific extent their IR and UV-VIS spectra. Absorption analysis in infrared constitutes a simple method for characterizing fulvic and humic acids from wastewater treatment plants. The extracted fulvic acids were characterized by moderate maturity, while humus acids were well developed. In the fermentation process, the N bond increases together with the level of humification of the humus acid. The characteristics of the extracted humus acids comply with other humic substances presented in the literature. Quantitative analysis showed that digested sludge contains, on average: FA from 5.07 to 5.30 g/kg dry matter, αHA from 59.22 to 74.72 g/kg dry matter, HMA from 20.31 to 43.66 g/kg dry matter. It was thus demonstrated that wastewater treatment, in particular digested sludge, constitutes an attractive source of humus acids with a wide range of applications in numerous areas, such as agriculture, ecological rehabilitation, environmental protection, animal breeding, aquaculture, veterinary as well as medicine and is a precious source of soil fertilizers.

Biotechnological Enhancement of Probiotics through Co-Cultivation with Algae: Future or a Trend?

The diversity of algal species is a rich source of many different bioactive metabolites. The compounds extracted from algal biomass have various beneficial effects on health. Recently, co-culture systems between microalgae and bacteria have emerged as an interesting solution that can reduce the high contamination risk associated with axenic cultures and, consequently, increase biomass yield and synthesis of active compounds. Probiotic microorganisms also have numerous positive effects on various aspects of health and represent potent co-culture partners. Most studies consider algae as prebiotics that serve as enhancers of probiotics performance. However, the extreme diversity of algal organisms and their ability to produce a plethora of metabolites are leading to new experimental designs in which these organisms are cultivated together to derive maximum benefit from their synergistic interactions. The future success of these studies depends on the precise experimental design of these complex systems. In the last decade, the development of high-throughput approaches has enabled a deeper understanding of global changes in response to interspecies interactions. Several studies have shown that the addition of algae, along with probiotics, can influence the microbiota, and improve gut health and overall yield in fish, shrimp, and mussels aquaculture. In the future, such findings can be further explored and implemented for use as dietary supplements for humans.

Biochemical Fulvic Acid Modification for Phosphate Crystal Inhibition in Water and Fertilizer Integration

Biochemical fulvic acid (BFA), produced by organic wastes composting, is the complex organic matter with various functional groups. A novel modified biochemical fulvic acid (MBFA) which possessed stronger chelating ability had been synthesized by the grafting copolymerization of BFA and acrylic acid (AA). Results showed that MBFA effectively inhibited the crystallization of calcium phosphate and increased the concentration of phosphate in water solution. The optimum reaction conditions optimized by Box–Behnken design and response surface methodology were reaction temperature 69.24 °C, the mass of monomer to fulvic acid ratio 0.713, the initiator dosage 19.78%, and phosphate crystal-inhibition extent was 96.89%. IR spectra demonstrated AA was grafted onto BFA. XRD data and SEM images appeared the formation and growth of calcium phosphate crystals was effectively inhibited by MBFA.

Cyanobacteria: A Natural Source for Controlling Agricultural Plant Diseases Caused by Fungi and Oomycetes and Improving Plant Growth

Cyanobacteria, also called blue-green algae, are a group of prokaryotic microorganisms largely distributed in both terrestrial and aquatic environments. They produce a wide range of bioactive compounds that are mostly used in cosmetics, animal feed and human food, nutraceutical and pharmaceutical industries, and the production of biofuels. Nowadays, the research concerning the use of cyanobacteria in agriculture has pointed out their potential as biofertilizers and as a source of bioactive compounds, such as phycobiliproteins, for plant pathogen control and as inducers of plant systemic resistance. The use of alternative products in place of synthetic ones for plant disease control is also encouraged by European Directive 2009/128/EC. The present up-to-date review gives an overall view of the recent results on the use of cyanobacteria for both their bioprotective effect against fungal and oomycete phytopathogens and their plant biostimulant properties. We highlight the need for considering several factors for a proper and sustainable management of agricultural crops, ranging from the mechanisms by which cyanobacteria reduce plant diseases and modulate plant resistance to the enhancement of plant growth.

Microalgae as biostimulants: a new approach in agriculture

This review aims to elucidate the state of the art of microalgae-based biostimulants as a tool in agriculture by summarizing the biologically active compounds factors that influence the use of microalgae biostimulants and their application methods in the field. Additionally, we examined the factors that support the use of microalgal biostimulants to face abiotic and biotic stress in crop plants. The use of microalgae in crop production and the benefits of seed preparation, foliar application, soil drenching, and hydroponic treatments were discussed. Furthermore, the use of these biostimulants in crop plants and their multiple benefits such as, better rooting, higher crop, fruit yields, drought and salinity tolerance, photosynthetic activity and pathogen resistance was thoroughly presented. The present situation of microalgal biostimulants and their difficulties in the market was analyzed, as well as the perspectives of their use. However, data shows that microalgal derived biostimulants can be used as an alternative for the protection of crops and plant growth regulators and play a significant key role in increasing the levels of production, yield and health of crops. Special interest needs to focus on investigating more microalgae species and their biological active compound factors, due to the largely untapped field. Perspectives regarding future research lines and development priorities were included.

Algae biofertilisers promote sustainable food production and a circular nutrient economy - An integrated empirical-modelling study

Agriculture has radically changed the global nitrogen (N) cycle and is heavily dependent on synthetic N-fertiliser. However, the N-use efficiency of synthetic fertilisers is often only 50% with N-losses from crop systems polluting the biosphere, hydrosphere and atmosphere. To address the large carbon and energy footprint of N-fertiliser synthesis and curb N-pollution, new technologies are required to deliver enhanced energy efficiency, decarbonisation and a circular nutrient economy. Algae fertilisers (AF) are an alternative to synthetic N-fertiliser (SF). Here microalgae were used as biofertiliser for spinach production. AF production was evaluated using life-cycle analyses. Over 4 weeks, AF released 63.5% of N as bioavailable ammonium and nitrate, and 25% of phosphorous (P) as phosphate to the growth substrate; SF released 100% N and 20% P. To maximise crop N-use and minimise N-leaching, we explored AF and SF dose-response-curves with spinach in glasshouse conditions. AF-grown spinach produced 36% less biomass than SF-grown plants due to AF's slower and linear N-release; SF exhibited 5-times higher N-leaching than AF. Optimised AF:SF blends yielded greater synchrony between N-release and crop-uptake, boosting crop yields and minimising N-loss. Additional benefits of AF included greener leaves, lower leaf nitrate concentration, and higher microbial diversity and water holding capacity of the growth substrate. An integrated techno-economic and life-cycle-analysis of scaled-up microalgae systems (+/- wastewater) normalised to the application dose showed that replacing the most effective SF-dose with AF lowered the annual carbon footprint of fertiliser production from 3.644 kg CO₂ m^-2 (C-producing) to -6.039 kg CO₂ m^-2 (C-assimilation). N-loss from growth substrate was lowered by 54%. Embodied energy for AF:SF blends could be reduced by 29% when cultivating microalgae on wastewater. Conclusions: (i) microalgae offer a sustainable alternative to synthetic N-fertiliser for spinach production and potentially other crop systems, (ii) microalgae biofertilisers support the circular-nutrient-economy and several UN-Sustainable-Development-Goals.

Microbial Biostimulants as Response to Modern Agriculture Needs: Composition, Role and Application of These Innovative Products

An increasing need for a more sustainable agriculturally-productive system is required in order to preserve soil fertility and reduce soil biodiversity loss. Microbial biostimulants are innovative technologies able to ensure agricultural yield with high nutritional values, overcoming the negative effects derived from environmental changes. The aim of this review was to provide an overview on the research related to plant growth promoting microorganisms (PGPMs) used alone, in consortium, or in combination with organic matrices such as plant biostimulants (PBs). Moreover, the effectiveness and the role of microbial biostimulants as a biological tool to improve fruit quality and limit soil degradation is discussed. Finally, the increased use of these products requires the achievement of an accurate selection of beneficial microorganisms and consortia, and the ability to prepare for future agriculture challenges. Hence, the implementation of the microorganism positive list provided by EU (2019/1009), is desirable.