NH4NO3 N-addition overstates steppe microbe effects
In Inner Mongolian steppe, acidic NH4NO3 and (NH4)2SO4 shifted soil bacteria and carbon-gene profiles more than urea or NH4HCO3, so NH4NO3-only experiments can overestimate real N-deposition effects.
Source
Nitrogen deposition experiment mimicked with NH<sub>4</sub>NO<sub>3</sub> overestimates the effect on soil microbial community composition and functional potential in the Eurasian steppe
Inspect source passages
NH4NO3 N-addition overstates steppe microbe effects
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NH4HCO3 raised Actinobacteria 9.68% versus 24.97% for NH4NO3.
For example, when the addition of NH 4 HCO 3 increased the relative abundances of phylum Actinobacteria by only 9.68% (Table ), adding NH 4 NO 3 resulted in an increase of 24.97%.
What shortcut do >50% of N-deposition experiments use?
mimicked N deposition by adding NH 4 NO 3
What they did
Authors applied control, NH4NO3, (NH4)2SO4, urea, slow-release urea, and NH4HCO3 in a Eurasian steppe (four replicates) and compared plant biomass, soil chemistry, 16S composition, and microbial functional genes.
What they found
Only acid N salts clearly acidified soil, raised NH4+, cut belowground biomass, and shifted bacteria (more Actinobacteria/Alphaproteobacteria, fewer Acidobacteria/Chloroflexi) plus recalcitrant-C genes. NH4NO3 raised Actinobacteria 24.97% versus 9.68% for NH4HCO3.
The limits
What it doesn't show
A single-steppe, multi-compound addition is not a full map of atmospheric N speciation everywhere; plant community composition did not shift even where microbes did.
Key terms
- N deposition
- Atmospheric nitrogen from fertilizer and fossil-fuel sources landing on ecosystems.
- NH4NO3 mimic
- Common experimental shortcut adding ammonium nitrate as if it represented all deposited N.
- Acid N compounds
- NH4NO3 and (NH4)2SO4, which acidify soil more than urea or NH4HCO3.
- Eurasian steppe
- Grassland biome here represented by an Inner Mongolia field experiment.
- Functional genes
- Microbial genes for carbon degradation and other processes, profiled beyond taxonomy.
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Quiz yourself
NH4NO3-only N-addition experiments here:
Common questions
Why not use only NH4NO3?
Real deposition is a mix; NH4NO3 overstated microbial change versus NH4HCO3.
Which compounds hit microbes hardest?
Acid salts NH4NO3 and (NH4)2SO4.
Main soil correlate of bacterial composition?
Soil NH4+-N content.
Did plants’ species mix change?
No significant plant-composition effect.
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