Strain-Specific Biostimulant Effects of Chlorella and Chlamydomonas Green Microalgae on Medicago truncatula

Abstract

Microalgae have been identified to produce a plethora of bioactive compounds exerting growth stimulating effects on plants. The objective of this study was to investigate the plant-growth-promoting effects of three selected strains of eukaryotic green microalgae. The biostimulatory effects of two Chlorella species (MACC-360 and MACC-38) and a Chlamydomonas reinhardtii strain (cc124) were investigated in a Medicago truncatula model plant grown under controlled greenhouse conditions. The physiological responses of the M. truncatula A17 ecotype to algal biomass addition were characterized thoroughly. The plants were cultivated in pots containing a mixture of vermiculite and soil (1:3) layered with clay at the bottom. The application of live algae cells using the soil drench method significantly increased the plants’ shoot length, leaf size, fresh weight, number of flowers and pigment content. For most of the parameters analyzed, the effects of treatment proved to be specific for the applied algae strains. Overall, Chlorella application led to more robust plants with increased fresh biomass, bigger leaves and more flowers/pods compared to the control and Chlamydomonas-treated samples receiving identical total nutrients.

Foliar Spray or Soil Drench: Microalgae Application Impacts on Soil Microbiology, Morpho-Physiological and Biochemical Responses, Oil and Fatty Acid Profiles of Chia Plants under Alkaline Stress

“…Microalgae are used as biofertilizers because of their high content of bioactive components, including pigments (chlorophyll a, b, β-carotene, phycobilin, phycoerythrin, and xanthophyll), phenolics, peptides, and lipids [ 54 ], as well as high protein content and levels of micronutrients, polyamines, natural enzymes, carbohydrates, amino acids, and vitamins [ 55 ], all of which affect overall plant metabolism, synthesis of photosynthetic pigments, and enzymatic activity, causing an improvement in plant growth and productivity. Furthermore, microalgae contributed to an increase in endogenous hormone content, which is responsible for branch development, postponing leaf senescence, and floral transition [ 56 ]. Under stress conditions, microalgal can alter certain biochemical processes to produce antagonistic compounds, leading to plant tolerance [ 57 ].…”

“…Soil drenching application provides plants with the required nutrients slowly, enhances the nutrient availability in the root zone, and improves the yield traits [ 64 ]. Soil drenching appears to primarily affect the Krebs cycle in terms of carbon metabolism, as seen by the simultaneous increase in citrate synthase and malate dehydrogenase enzymes [ 56 ]. These results are in line with the findings obtained by Mohamadineia et al [ 65 ], Faheed and Abd-El Fattah [ 66 ], Agathokleous et al [ 67 ], Puglisi et al [ 68 ], and Suchithra et al [ 69 ], but disagree with Li et al [ 70 ], who found that foliar application of microalgae extract was more successful than soil drenching in promoting the growth and quality of seeds.…”

Saline‐alkali land amendment and value development: Microalgal biofertilizer for efficient production of a halophytic crop ‐ Chenopodium quinoa

“…Besides, the chlorophyll synthesis and photosynthetic activity in photosystem II of quinoa were all improved when treated with algal additions (Figure 4). The soil drench of living Chlorella cell was also proved that can improve the pigment content of Medicago truncatula and Abelmoschus angulosus (Gitau et al, 2021; Umamaheswari & Shanthakumar, 2020). The production of more chlorophyll enhances the photosynthesis in living organism that is the process wherein solar energy is used to synthesize organic compounds for main biomass and nutrient accumulation (Hou et al, 2021).…”

“…For microalgal biostimulant, the applications of microalgal products provide protection for crops against saline environment, for instance, wheat using Spirulina and Chlorella extracts, and pepper using Dunaliella and Phaeodactylum extracts, which might be attributed to the stimulation of antioxidant systems including enzyme activity, carotenoid, tocopherol, phenolic, and protein, leading to a reduction in superoxide radical production (Abd El‐Baky et al, 2010; Arroussi et al, 2018; Guzmán‐Murillo et al, 2013). For microalgal living cell biofertilizer, the application of living Chlorella cell led to more robust plants (Gitau et al, 2021), and furthermore, Solanum lycopersicum after Acutodesmus dimorphus culture treatment showed more positive effects on seed germination and plant growth than the extract (Garcia‐Gonzalez & Sommerfeld, 2016). In conclusion, it is not difficult to speculate that the survival ability of microalgae in special habitats is the precondition for their optimal effects.…”

Photosymbiotic tissue engineering and regeneration

“…It is a mutualistic relationship whereby the photosynthetic partner, known as symbiont, supplies photosynthetic products such as O 2 and glucose to its host which, in turn, provides a nutrient-rich microenvironment and protection from predators [76]. One of the known examples of photosymbiosis involves the photosynthetic microalgae that form symbioses with bacteria [77], ciliates [78], fungi [79], plants [80], and vertebrates including sloths [9] and spotted salamanders [8,81]. A unique photosymbiotic association occurs between microalgae, Oophila amblystomatis, and embryos of the spotted salamander whereby microalgae enter the cells of the salamander during early development [82].…”