Dataset on Quantifying Relative Contributions of Dissimilatory Nitrate Reduction to Ammonium and Denitrification in Mangrove Soils
Description
This dataset comes from anoxic mangrove soil pre-incubation and incubation experiments (with ambient vs. iron-enriched conditions). It measures how much of the added nitrate is converted to ammonium via DNRA compared to how much is lost as nitrogen gas through denitrification.
Files
Steps to reproduce
1 Soil Collection and Preparation: Fifteen surface soil samples (0–5 cm depth) were collected from a mangrove forest (Zhangjiang Estuary Reserve, China). Samples were kept at 4°C in the dark during transport, then combined and homogenized into one mixed soil. The mixed soil was split into two parts: one for initial characterization (e.g., organic C and Fe content) and one for the incubation experiments. 2 Anoxic Pre-Incubation: The soil was mixed with sterile artificial seawater at a 1:3 (w/v) ratio to create a slurry, which was split into two treatments: raw mangrove soil (RMS) and iron-enriched mangrove soil (IEMS). Both were incubated at 25°C in the dark under anoxic conditions. After 4 days, FeCl₂ was added to IEMS to increase Fe(II) concentration by approximately 15 mM relative to RMS, and NaOH was added to adjust the pH to 7.7 (matching RMS). The slurries then continued anoxic incubation for 45 days until conditions stabilized. 3 Incubation Experiment: After pre-incubation, RMS and IEMS slurries were well-mixed and dispensed (30 mL each) into 120 mL serum bottles under anoxic conditions. Each bottle received one of three treatments: (i) Control (no added NO₃⁻ or NO₂⁻), (ii) +NO₃⁻ (NaNO₃ added to 2 mM), or (iii) +NO₂⁻ (NaNO₂ added to 1 mM). Bottles were sealed and incubated at 25°C in the dark for 144 hours (6 days). Each treatment was prepared in duplicate for both RMS and IEMS. 4 Gas and Slurry Sampling: At set intervals during the incubation, headspace gas and slurry samples were collected. Each bottle was gently shaken, then 0.5–1 mL of headspace gas was withdrawn with a gas-tight syringe and injected into a gas chromatograph (GC-ECD) to measure N₂O. Immediately after, the bottle was opened inside the anoxic chamber to sample the slurry. Slurry pH and Eh were measured with electrodes. For Fe(II) analysis, 100 µL of slurry was added to a sulfamic acid/HCl solution (to prevent Fe(II) oxidation) and shaken 2 h, then centrifuged (10,000 rpm, 10 min) and filtered (0.22 µm). The Fe(II) concentration in the extract was determined by a ferrozine colorimetric assay (absorbance of the Fe(II)-ferrozine complex). Dissolved Fe(II) was measured similarly, except the slurry was filtered (0.22 µm) prior to sulfamic acid treatment. 5 Nutrient and DOC Extraction/Analysis: After gas and Fe sampling, the slurry was used to extract inorganic N and dissolved organic carbon (DOC). The slurry was briefly bubbled with O₂ (2 min) to halt anaerobic reactions. Then, 6 mL of slurry was mixed with 30 mL of 2 M KCl (pH 7) to extract NO₃⁻, NO₂⁻, and NH₄⁺, and 4 mL was mixed with 20 mL of 0.5 M K₂SO₄ to extract DOC. Each mixture was shaken (2 h), centrifuged (10,000 rpm, 10 min), and filtered (0.22 µm for KCl; 0.45 µm for K₂SO₄). Nitrate, nitrite, and ammonium in the KCl extracts were measured using a continuous-flow autoanalyzer, and DOC in the K₂SO₄ extracts was measured with a TOC analyzer.
Institutions
- Fenyang College Shanxi Medical University