Is nitrate reduction to nitrite possible in glucose-amended alkaline saline soil under aerobic conditions?

Abstract

A phylogenetic analysis of the archaeal community in the soil of the former Lake Texcoco showed that some of the clones identified were affiliated to Archeae that reduce nitrate (NO 3 −) to nitrite (NO 2 −) and NO 2 − to unknown products under aerobic conditions. Previous research suggested that this indeed might occur when an easily decomposable C-substrate is available, but little is known about the factors that control the possible processes involved. The sandy clay loam soil with pH 10 and electrolytic conductivity 56 dS m −1 was spiked with 1000 mg glucose-C kg −1 soil (GLUCOSE pre-treatment), 200 mg NO 3 −-N kg −1 soil (NITRATE pre-treatment), or left unamended (CONTROL pre-treatment) and conditioned for eight days. Pre-treated soil was then added with 1000 mg glucose-C kg −1 soil and 200 mg NO 3 −-N kg −1 soil and amended with ammonium (NH 4 +) (AMM treatment) and l-glutamine (GLUT treatment), acetylene (C 2H 2) (ACE treatment), oxygen (O 2) (OXI treatment), left untreated (CON treatment) or sterilized. No abiotic factors affected concentrations of NH 4 +, NO 2 − or NO 3 −. In the CONTROL pre-treatment, concentration of NO 3 − decreased 170 mg N kg −1 soil within 72 h, in the GLUCOSE pre-treatment with 182 mg N kg −1 soil within 2 h and in the NITRATE pre-treatment with 272 mg N kg −1 soil within 168 h. Mean concentration of NO 2 − was 3.2 mg N kg −1 soil in unamended soil, 5.7 mg N kg −1 soil in the CONTROL pre-treatment, but >20 mg kg −1 soil in the GLUCOSE pre-treatment and ≥40 mg kg −1 in the NITRATE pre-treatment. The application of NO 3 − and glucose increased the mean concentration of NH 4 + compared to the unamended soil independently of pre-treatment. It was found that microorganisms in the alkaline saline soil of the former Lake Texcoco can reduce concentrations of NO 3 − while releasing NO 2 − under aerobic conditions when an easy decomposable substrate is available without it being directly related to microbial activity and this being more outspoken when glucose or nitrate were previously added.