Effects of Engineered Nanoparticles On Soil Nitrogen Mineralization and Nitrification.

Engineered nanoparticles (ENPs) can show antibacterial activity in pure culture conditions, which implies that ENPs may be important environmental toxins. However, little is known about the effects of ENPs on complex microbial communities and processes in terrestrial ecosystems. Nitrogen (N) mineralization and nitrification are two processes in the soil N cycle. These processes supply most of the N used by terrestrial plants, and nitrification is critical in regulating N₂O and NO fluxes to the atmosphere. This study aims to quantify the effects of two widely-used nanoparticulate metal oxides (TiO₂ and ZnO) on soil N mineralization and nitrification by incubating microcosms (for 15, 30, 45 and 60 days) with different concentrations of TiO₂ (0, 500, 1000 and 2000 µg g^-1 fresh soil) and ZnO (50, 100 and 500 µg g^-1 fresh soil). We measure net mineralization and nitrification, and use ¹⁵N dilution to measure gross NH₄⁺ and NO₃^- turnover rates. Total respiration by CO₂ production is measured from the headspace of sealed bottles prior to periodic venting. We also measure dehydrogenase, protease and chitinase activities for assessing overall community metabolism, and intra- and extracellular N depolymerization, respectively. Overall microbial and nitrifier community composition and diversity are examined by PCR T-RFLP, while biomass is measured by substrate induced respiration (SIR), the amount of total extracted DNA, and real-time PCR using group-specific primers. The bioavailability of ENPs is assessed by extracting the soil solution, then analyzing it by ICP-MS for total Ti and Zn. This study is advancing our understanding of the environmental and ecological risks of ENPs in terrestrial ecosystems.