The Fate and Distribution of Microalgal Nitrogen When Applied as an Agricultural Soil Fertiliser and Its Effect on Soil Microbial Communities

Global estimates show that less than half the nitrogen fertiliser inputs to agricultural soil are taken up by crops. The remaining inorganic nutrients follow several pathways, with run off into nearby waterbodies being particularly problematic, contributing to the formation of algal blooms. A proposed solution is to recover the algae biomass from receiving waterbodies and apply it back to the land to replenish soil nutrients and enable a reduction in the need for inorganic fertilizers. A N-15 tracer study was performed under greenhouse conditions, where labelled algal N (55.75% atom% N-15) was added to soil at 15.8 mg N/500 g soil) to assess the fate of nitrogen derived from a common unicellular green alga, Chlorella vulgaris, into soil and wheat nitrogen pools, with an assessment of the impact on soil bacterial communities. The soil retained a higher amount of algal nitrogen (10.3%) compared to the wheat shoot (0.7%) after 30 days, corresponding to the results of the 16S rDNA sequencing, which demonstrated that the algal biomass increased microbial diversity after 30 days and changed the relative abundance of microbial taxa putatively involved in facilitating the breakdown of organic residues. These findings provide useful insights into the application of algae biomass to agricultural soils to influence nitrogen fertilization and improve soil health through the increase in soil microbial diversity.