Abstract
Ammonia-oxidizing archaea (AOA) dominate nitrification in acidic soils, and the split between neutrophilic Nitrososphaerales (NS) and acidophilic Nitrosotalea (NT) is the clearest ecological division within the group, though its response to pH has never been fitted as a continuous curve. We estimated it using 351 soil cores from 40 NEON terrestrial sites, joining amoA-assigned 16S data to same-core measured pH.
The turnover completes before soils reach neutrality. NS holds 17.9% of the archaeal ammonia-oxidizer pool below pH 4.5 and 99.8% above pH 6.5, rising steeply in a segmented model (+0.93 per pH unit, z = 4.70) to a breakpoint near pH 6.1 before flattening, a fit gaining 36.6% of log-linear deviance against a no-threshold null (P < 0.005). NT declines log-linearly across the entire gradient with no breakpoint, and because the amoA reference names it better as pH rises, that decline is a floor, not an estimate.
The share of a core's nitrogen sitting in the mobile, leachable form rises across the whole gradient with no plateau, unlike nitrification efficiency; together the two curves place the last demonstrable conversion gain from liming at pH ≈ 6.25, near where a projected pH-resolved N₂O emission factor also peaks under every yield shape tested.