A b s t r a c t. The actual denitrification to N 2 O and denitrification capacity to N 2 O after flooding of different soil samples stored for over 25 years in air-dry conditions and fresh, air dried samples were compared in our study. Zero N 2 O release was observed from the stored soils but the fresh soil samples had very low actual denitrification to N 2 O. NO 3 -addition significantly increased the amount of N 2 O (denitrification capacity to N 2 O) released after flooding, which depended on the length of storage and type of soils and was much higher in stored soils. Prolonged exposure of the soils to drought conditions caused a greater decrease in the Eh value compared with the fresh soil. The total cumulative release of N 2 O from the stored and fresh soils was correlated with the reduced NO 3 -and organic C content in soils enriched with NO 3 -. Some soils showed the capability of N 2 O consumption. CO 2 release depended on the length of storage and type of soils under flooding after prolonged drought. On average, CO 2 release was higher from the stored rather than fresh soils. The organic C content in the stored soils was generally lower than in the fresh soils, probably due to the storage effect. The cumulative CO 2 release from the stored soils was well correlated with the organic C while no correlation was observed for the fresh soil samples.K e y w o r d s: actual denitrification to N 2 O, denitrification capacity to N 2 O, long-and very short-storage time, soil respiration, archived soil INTRODUCTIONBiological activity in soil can be represented by several different parameters such as respiration, enzyme activity, ammonification, nitrification, denitrification, and emission of gaseous metabolites as well as oxidation-reduction processes (Bieganowski et al., 2013;W³odarczyk et al., 2011).Soils are subjected to temporal variations in temperature and moisture that can cause changes in physicochemical properties. Soil dry/wet cycles result from natural variations in soil moisture driven by environmental and biophysical processes such as precipitation, evapotranspiration, and drainage. Management factors such as irrigation, tillage and land cover (ie. vegetation type) can moderate or accentuate the amplitude of these natural cycles (Oliveira et al., 2005).Under in situ conditions, denitrification rates depend on oxygen availability, soil moisture, soil type, pH, NO 3 -concentration, but also on the availability of labile carbon compounds in soil (Burford and Bremner, 1975; Senbayram et al., 2009). Nitrate (NO 3 -) is a key node in the network of the assimilatory and respiratory nitrogen pathways. For bacteria, it is both a nitrogen source and an electron acceptor (Hayatsu et al., 2008). In agriculture and wastewater treatment, NO 3 -respiration by microorganisms is an important process in respect to economics, greenhouse gas emission, and public health. Several microbial processes compete for NO

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% CaCl 2 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 NO 3 in non-flooded soils, which can be beneficial in terms of reducing N leaching. Encapsulated microalgae seemed to have assimilated NH 4 + 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 NO 3 and NH 4

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