Sustainability of microalgae fertilization above and belowground

The microalgae have attracted interest as a promising approach for the implementation of a sustaina-ble wastewater treatment technology because of its high effectiveness in recovering nutrients and low-cost. We focused our work on closing the cycle of comprehensive understanding of what is the impact of microalgae, produced from toilet human waste, as a biofertilizer aboveground accessing the atmosphere with the impact of greenhouse gases (GHG) emissions, and belowground for the soil chemistry and microorganisms for bulk and rhizosphere including specific functions of nitrogen cycle and middle-ground with plant productivity and quality. Here, we applied a greenhouse experiment to assess the impact of different nitrogen sources (control without fertilization, NPK, and microalgae biofertilizer) on active soil microbiomes (bacteria and protists) in different time points targeting different plant development stages to access the rhizosphere and its surrounding. Overall, microalgae application showed same plant productivity but also higher grains nutrients concentration than NPK. Furthermore, we observed that area-scale cumulated on average 4.6-fold higher nitrous oxide (N2O) emission, main GHG emitted from agriculture practices, to organic compared to inorganic treatment indicating nitrification as likely pathway responsible for N2O emission. We also found that the application of nitrogen fertilizers affected both bacterial and protozoan communities, but this outcome was masked because of the plant effect in the distinct developments stages. Although distributed differently through time, we observed that all three treatments enriched similar orders showing stability mainly for bacteria across the growth period. Together, our results suggest that microalgae is an optional fertilizer for increase productivity and has no visible unsatisfactory primary impact on bacterial and protozoan community and productivity, but as expected for an organic fertilizer, more studies are needed to rationalize it is application to reduce N2O emissions.