Ocena oddziaływania związków selenu oraz benzyny na aktywność wybranych enzymów przemian związków azotu w glebie

W pracy przedstawiono wyniki oddziaływania benzyny oraz selenu (IV) i (VI), na aktywność wybranych enzymów przemian azotu w glebie. Badania prowadzono w doświadczeniu laboratoryjnym na glebie zakwalifikowanej jako piasek gliniasty o zawartości węgla organicznego 8,7 g·kg⁻¹ s.m. Do próbek gleby wprowadzono w różnych kombinacjach kwas selenowy (IV) lub kwas selenowy (VI) (ilość dodanego Se wynosiła 0,05 mmol·kg⁻¹ s.m.) oraz benzynę w ilościach 2, 10 i 50 g·kg⁻¹ s.m. Wszystkie próbki doprowadzono do 60% maksymalnej pojemności wodnej i inkubowano w stałej temperaturze 20°C. W 1., 7., 14., 28. i 56. dniu doświadczenia oznaczono spektrofotometrycznie aktywność reduktazy azotanowej, ureazy oraz proteaz. Wprowadzenie do gleby benzyny w dawce 2 g·kg⁻¹ s.m. wywołało stymulację aktywności ureazy oraz reduktazy, podczas gdy większe dawki benzyny inhibitowały aktywność enzymów przemian azotu w glebie lekkiej. Po dodaniu selenu, zwłaszcza Se (VI) do gleby zanieczyszczonej benzyną w dawkach 10 i 50 g·kg⁻¹ s.m. stwierdzono głównie stymulację oznaczanych enzymów, zwłaszcza reduktazy azotanowej.

This paper describes the impact of selenium in two oxidation states (IV and VI) and gasoline on activity of enzymes involved in nitrogen transformations in soil: nitrate reductase (EC 1.6.6.1), urease (EC 3.5.1.5) and proteases (EC 3.4.4.x). The experiment was carried out in laboratory conditions on a soil material taken from the topsoil of Brunic Arenosol. According to the classification of the United States Department of Agriculture, it was soil with a granulometric composition of loamy sand with organic carbon content of 8.7 g·kg⁻¹ d.m. and total nitrogen content 0.97 g·kg⁻¹ d.m. Different combinations of selenic (IV) acid or selenic (VI) acid (the Se amount was 0.05 mmol·kg⁻¹) and gasoline at the dosages of 2, 10 i 50 g·kg⁻¹ d.m. were added to soil samples. All samples were adjusted to 60% of the maximum water holding capacity and stored at a temperature of 20°C. Activity of nitrate reductase, urease and proteases was determined on days 1, 7, 14, 28 and 56 using spectrophotometer UV-1800 (Shimadzu) in three repetitions. The results were examined using Tukey’s HSD test (p <0.05) and two-way η² analysis. Basing on obtained results there was also calculated influence factor of selenium. Which equals to quotient of activity of enzyme in soil with selenium and activity in control sample or with contamination. Soil treatment with gasoline at the dosage of 2 g·kg⁻¹ d.m. increased activity of nitrate reductase and urease during whole experiment except day 1 for nitrate reductase. Higher gasoline dosages caused inhibition of all measured enzymes. Application of Se (VI) to soil contaminated with gasoline at dosage 10 g·kg⁻¹ d.m. caused stimulation of nitrate reductase and proteases in all days of experiment. Selenium (IV) in soil with gasoline at the dosage 50 g·kg⁻¹ d.m. caused stimulation of all measured enzymes except day 1 for protease and urease. The η² analysis showed that gasoline had higher effect on activity of assayed enzymes than selenium, and percentage participations of this factors in the formation of nitrate reductase, urease and proteases were 88.66, 81.07 and 51.16%, respectively. Percentage participation of selenium effect was considerably lower for all enzyme activities than gasoline impact.