Urea amendment decouples nitrification in hydrocarbon contaminated Antarctic soil

Area of Science:

• Environmental Microbiology
• Soil Bioremediation
• Polar Science

Background:

• Hydrocarbon contamination in polar regions threatens ecosystems.
• Engineered biopiles effectively remediate contaminated soils in Antarctica.
• Urea fertilizers, while aiding bioremediation, increase soil pH, ammonium, and nitrite.

Purpose of the Study:

• To investigate the impact of sustained nitrite accumulation on nitrifier communities in Antarctic biopiles.
• To understand the relationship between nitrite levels, soil chemistry, and nitrifier abundance.
• To identify alternative biostimulants to prevent nitrite buildup.

Main Methods:

• Field monitoring of Antarctic biopiles.
• Amplicon sequencing to assess microbial communities.
• Microfluidic quantitative PCR (qPCR) on field samples.
• Laboratory soil microcosms at controlled temperatures (7°C and 15°C).

Main Results:

• Persistent high nitrite levels (up to 76 ± 57 mg N/kg) were observed in urea-amended biopiles.
• Low Nitrospira to ammonia-oxidizing bacteria (AOB) ratios (<1:1) correlated with Nitrobacter inhibition and nitrite accumulation.
• Laboratory microcosms at 7°C replicated nitrite accumulation seen in field biopiles.
• Diammonium phosphate amendment prevented nitrite accumulation.

Conclusions:

• Urea-based fertilization in cold, alkaline Antarctic soils can lead to detrimental nitrite accumulation by inhibiting key nitrifying bacteria.
• The ratio of nitrite-oxidizing bacteria (NOB) to AOB is critical for managing nitrite levels.
• Diammonium phosphate is a promising alternative biostimulant for Antarctic soil bioremediation, avoiding excessive nitrite buildup.