Abbott GD

Böttcher J

Heumann S

Leinweber P

Rimmer DL

Schlichting A

Recently, indirect evidence was obtained for inhibition of soil net N mineralization by sterols in soil organic matter, which could have been caused by their antioxidant or antimicrobial properties. The objective of this study was to test the effect of potential inhibitors (i.e., individual compounds with known antioxidant and/or antimicrobial properties) on soil microbial mineralization processes during incubation for 7 and 14 d. A sandy agricultural soil was amended with four substances: two phenolic acids differing in their antioxidant capacity (AOC) (acetovanillone with no AOC, ferulic acid with large AOC), Trolox, an analogue of vitamin E (large AOC), and b-sitosterol (no AOC, but potential antimicrobial properties). The two compounds with large AOC (ferulic acid and Trolox) showed no significant inhibition of C and net N mineralization; and the Trolox amendment actually caused a significant increase in C and net N mineralization after 7 d of incubation. Acetovanillone with no measurable AOC caused a significant increase in C mineralization (109% of substance C added), indicating degradation of the substance, and a very pronounced negative net N mineralization within 7 d (–356%), which was interpreted as N immobilization. Only b-sitosterol showed strong inhibition of net N mineralization after 7 and 14 d (–59% and –26%, respectively) which was not interpreted as N immobilization, since there was no concomitant increase in C mineralization. Thus, an antimicrobial effect of b-sitosterol specificly on microorganisms of the N cycle was suggested, but there was no clear inhibitory effect caused by the antioxidant compounds

Effects of potentially inhibiting substances on C and net N mineralization of a sandy soil – a case study

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