Evaluation of the plant biostimulant effects of selected eukaryotic green microalgae

Microalgae are ubiquitous photosynthetic microorganisms found in nature. They have been reported to synthesize many bioactive chemicals that stimulate plant development. Our experiments aimed to examine the effects of three selected strains of eukaryotic green microalgae on plant growth. Two Chlorella species (Mosonmagyaróvár Algal Culture Collection (MACC)-360 and MACC-38) and a Chlamydomonas reinhardtii strain (cc124) were examined in Medicago truncatula, A17 ecotype, in the first portion of our investigation. First, using growth curves and microscopy, the growth patterns, cell size, and morphology of the microalgal strains were determined. In addition, their ability to synthesize auxins was evaluated. In the greenhouse, M. truncatula was grown in pots containing a mixture of vermiculite and soil (1:3) with a clay layer at the bottom. Living algae cells were applied to the plants using the soil drench method. The plants' physiological reactions to adding algal biomass were comprehensively studied. Microalgae substantially boosted the plant's stem length, leaf size, fresh weight, number of flowers, and pigment content. For most of the investigated factors, there was a strain-specific effect. Overall, the application of Chlorella sp. MACC-360 resulted in more robust plants with greater fresh biomass, larger leaves, and more flowers/pods than the control, which received the same total nutrients. In the second phase of the investigation, the biostimulant effects of Chlorella sp. MACC-360 and C. reinhardtii cc124 on Solanum lycopersicum (tomato) were studied. This study's first purpose was to determine whether the two strains had biostimulant effects on tomato plants. The significance of application mode and timing (plant age) was also studied. Thirdly, the strain-specific effects of the two algal strains were evaluated. Finally, transcriptome and metagenomic analyses were conducted to identify the molecular effect of algae and the microbial community of the rhizosphere. Tomatoes were grown in pots with a clay layer at the bottom and a mixture of soil and vermiculate (2:1). In two sets of trials, living algae and algal extract and living algae and spent media plus extracts were applied to the soil and plant leaves, respectively. In the first group, the culture suspension (treatment A) was centrifuged, the algae pellet was re-suspended in water to make (Treatment B), and this was applied weekly to the soil, while the algae extract (cell disrupted algae suspension – Treatment C) was sprayed on the leaves bi-weekly. Analyses were conducted on the blooming process, plant morphology, fruit characteristics, and pigment content. In the second set of tests, culture suspension (A) was administered weekly to the soil, and C was sprayed bi-weekly on the leaves. The kinetics of flowering, reproductive capability, and photosynthetic characteristics were investigated. Both algal strains enhanced the leaf pigments, fruit weight, and fruit diameter. The age of the plant at the onset of treatment was a significant determinant of the outcome; treatments initiated later (week 5) produced superior results than those initiated at a juvenile level (week 1). Chlorella sp. MACC-360 stimulated early blooming and fruit development, whereas C. reinhardtii cc124 greatly slowed these processes. Chlorella facilitated the transformation of light energy into chemical energy, whereas Chlamydomonas boosted the protection of photosynthetic parameters. Both strains increased leaf thickness and leaf temperature differential. Both algal strains enhanced crucial agronomically useful tomato processes. The upregulation of genes involved in systemic resistance demonstrated that microalgae readied plants to respond to abiotic stress and pathogen attacks, as evidenced by the transcription data. According to soil metagenomics research results, algae influenced the construction of the tomato rhizosphere microbiome. In soils saturated with microalgae, the number of Ascomycota fungus, Streptomyces, Brevundimonas, and other helpful bacteria that provided plant nutrition and defense against dangerous microbes increased

Chlorella, ¿un potencial biofertilizante?

Abstract Microalgae are photoautotrophic organisms with fast growth and the ability to adapt to different environments. They convert carbon dioxide into biomass and are considered to have great biotechnological potential because of it. Algal biomass can be used in food and bioactive compounds industry, in biofuels production, in bioremediation and biofertilization. As biofertilizers, chlorophytes and cyanophytes microalgae produce polysaccharides (mucilage) that can avoid erosion, improve the structure and organic matter content in the soil, and increase the ions concentration for crop plants. Thus, reducing the need for conventional crop chemical fertilizers. The use of this microalgae as biofertilizers is called algalization. Algalization uses mainly chlorophytes due to their high growth rate, their simple large scale cultivation, and their adaptation to soil conditions. Chlorella genus is of special interest because research has shown that it can help with nitrogen fixation, improve physical and chemical properties of the soil, and produce substances that can promote plant development and infections control. Therefore, microalgae from Chlorella genus are a viable alternative for biofertilization, generating benefits for agricultural production and the environment.Resumo As microalgas são organismos fotoautotróficos com crescimento rápido e capacidade de adaptação a diferentes ambientes. Eles convertem dióxido de carbono em biomassa e, por isso, são considerados com um grande potencial biotecnológico. A biomassa de algas pode ser usada na indústria alimentar e de compostos bioactivos, na produção de biocombustíveis, na biorremediação e biofertilização. Como biofertilizantes, as microalgas clorófitas e cianófitas produzem polissacarídeos (mucilagem) que podem evitar a erosão, melhorar a estrutura e o conteúdo de matéria orgânica do solo, e aumentar a concentração de iões nas culturas, reduzindo assim a necessidade de fertilizantes químicos convencionais. O uso dessas microalgas como biofertilizantes é chamado de algalização. Durante este processo, usam-se eles ​​principalmente clorofíceas por sua alta taxa de crescimento, facilidade de cultura em larga escala, e sua adaptação às condições do solo. A Chlorella é de grande interesse porque vários estudos têm mostrado que pode auxiliar na fixação do nitrogênio, melhorar as propriedades físicas e químicas do solo, e produzir substâncias que promovem o crescimento das plantas e o controle de infecções. Por esta razão, as microalgas do gênero Chlorella representam uma alternativa viável para a biofertilização, gerando benefícios não só para a produção agrícola, mas também para o meio ambiente.Resumen Las microalgas son organismos fotoautótrofos con un rápido crecimiento y la habilidad de adaptarse a diversos ambientes. Convierten el dióxido de carbono en biomasa y debido a esto, se considera que tienen gran potencial biotecnológico. La biomasa algal puede usarse en la industria alimenticia y de compuestos bioactivos, en la producción de biocombustibles, en la bioremediación y biofertilización. Como biofertilizantes, las microalgas clorofitas y cianofitas, producen polisacáridos (mucílago) que pueden evitar la erosión, mejorar la estructura y el contenido de material orgánica de los suelos, y aumentar la concentración de iones en los cultivos. Reduciendo de esta forma la necesidad de fertilizantes químicos convencionales. El uso de estas microalgas como biofertilizantes se denomina algalización. Durante este proceso se usan principalmente clorofitas por su alta tasa de crecimiento, la facilidad de su cultivo a gran escala, y su adaptación a las condiciones del suelo. El género Chlorella es de gran interés porque diversos estudios han mostrado que puede ayudar en la fijación del nitrógeno, mejorar las propiedades físicas y químicas del suelo, y producir sustancias que promueven el desarrollo de la planta y el control de infecciones. Por esta razón, las microalgas del género Chlorella representan una alternativa viable para la biofertilización, generando beneficios no solo para la producción agrícola sino también para el medio ambiente