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The current problem with phosphorus fertilizers are shortage of rock phosphate from which it is produced and adverse impact of their production and use on the environment. A promising solution is use of phosphorus-rich biomass of microalgae as biofertilizer, but possible impact of such fertilizers on the biological activity and microbiome of soils remain unknown in many aspects. We investigated the effect of Chlorella vulgaris IPPAS C-1 (Chlorophyceae) biomass application on yield, biological activity, efficacy of the rhizobia- and cyanobacteria-based growth promoting formulations, as well as the microbiome of the soil during cultivation of beans (Phaseolus vulgaris L.) cvr. “Strela.” Total and specific yield, actual nitrification and denitrification, carbon dioxide and methane emission were determined for soil samples from the rhizosphere. The taxonomic structure of the prokaryotic community of the bean rhizosphere was determined by NGS of 16s rRNA gene amplicons on the Illumina platform. The metagenomic data were analyzed using software tools QIIME and VAMPS. It was found that the application of biomass of C. vulgaris IPPAS C-1 as a phosphorus biofertilizer increased the bulk yield of beans. It also allowed to achieve the specific yield (per plant) level provided by traditional fertilizers. The biomass application did not (i) impact the biological activity of the soil, (ii) did not increase the level of denitrification, and (iii) did not increase significantly the soil emission of the “greenhouse gases.” The Chlorella biomass application hamper the growth-promoting effect of the bacterial preparations made from rhizobia and cyanobacteria. Also, no significant changes in the taxonomic composition of the soil of the rhizosphere microbiome upon the application of the Chlorella biomass were revealed. Collectively, the results indicate the possibility of at least partial replacement of chemical fertilizers with phosphorus biofertilizers from microalgae biomass in the field growing of beans.

Studies of the impact of inorganic phosphorus (Pi), an important nutrient, on the growth and physiological parameters of single-celled algae are important for investigations of the dynamics of phytoplankton abundance and productivity in natural ecosystems as well as in industrial systems for the cultivation of microalgae. Difficulties in carrying out such studies are associated with the complex kinetics of Pi uptake by cells and the ability of microalgae to store phosphorus in their cells. This situation necessitates efficient methods for express monitoring of microalgal cultures, such as the methods based on the registration of optical properties of cells, in particular absorption and scattering of light and fluorescence of chlorophyll contained in the cells. Here, the results of monitoring the cultures of the chlorophyte Chlorella vulgaris IPPAS C-1 starving for phosphorus are described. It was found that both optical (light absorption in the bands of the key pigments—chlorophylls and carotenoids) and luminescent (variable fluorescence of chlorophyll) parameters closely reflect the culture condition. Registration of optical properties required correction for the contribution of light scattering to the overall extinction of light by microalgal cell suspensions. At the same time, the light scattering signal is an accurate measure of the total number of suspended particles in the suspension. However, it is difficult to monitor cultures containing a significant amount of light-scattering particles lacking photosynthetic pigments (such as heterotrophic bacteria). For such cultures, the use of variable fluorescence- based parameter Fv/Fm reflecting the maximum photochemical efficiency of the photosystem II is advisable.