Abstract
Soil pH is a major ecological factor influencing archaeal communities involved in ammonia oxidation within soil. The relative balance of Nitrososphaerales (NS) and Nitrosotaleales (NT) across soil pH gradients in North America remains poorly characterized. Motivated by observed NS predominance in soil samples taken from a Virginia orchard under regenerative management, we extended the analysis to 351 National Ecological Observatory Network (NEON) soil cores spanning 40 North American sites, with water pH ranging from 3.48 to 9.57. NS and NT were identified from SILVA order-level assignments, and their relative balance was evaluated with NS share, 100 × NS / (NS + NT). Each retained core contained at least 50 combined NS and NT reads. Across the continental dataset, NS share generally increased with pH, shifting from broad variation in acidic soils to clustering near 100% at higher pH. Above pH 6.5, 107 of 111 cores (96.4%) had NS shares of at least 99%, revealing a striking compositional shift across geographically and environmentally heterogeneous soils. Thirteen samples from a distressed orchard soil under regenerative management in Virginia were evaluated as an independent case comparison. Their pH ranged from 6.5 to 7.6, and 11 of 13 samples had NS shares of at least 99%, placing most farm observations within the high-pH range. These results identify a prominent continental pH-associated transition in NS–NT composition.