Effect of encapsulated and free-living cells of Chlorella vulgaris L. On nitrogen retention in soils

Abstract

We hypothesised that the addition of free-living and alginate-encapsulated algae Chlorella vulgaris to the soil would change the availability of soluble forms of nitrogen, increasing the retention of nitrates, which is especially important due to fertilisers misuse and nitrogen leaching. C. vulgaris were grown on Knop and Baslerowa-Dvorakova media. The best growth was observed on Knop medium in 25ºC. Three different soils (Brunic Arenosol, Haplic Umbrisol, Mollic Umbrisol) were tested in both flooded conditions and conditions corresponding to field water capacity. Capsules prepared with 1.0-2.5% sodium alginate and 0.5-5% CaCl2 kept shape and consistency, but at a different level of durability. From nine different concentrations of alginate used to form the capsules, 1% proved to be the most suitable. In contrast to encapsulated C. vulgaris, the addition of free-living algae had a positive effect on the reduction of NO3- in non-flooded soils, which can be beneficial in terms of reducing N leaching. Encapsulated microalgae seemed to have assimilated NH4+ under flooded conditions, but this effect was generally blurred by alginate capsule sorption/adsorption. In two sandy and one silty soil, encapsulated algae were rather ineffective, and their impact was limited to a minor reduction of NO3- and NH4+ content under flooded conditions.