FIG 9.

Root and cropping system influences on ammonia oxidizer abundance and nitrification. (A to F) AOB amoA gene abundance (A); AOA amoA gene abundance (B); AOB/AOA ratio (C); potential nitrification activity (D); gross nitrate production (¹⁵NO₃ pool dilution) (E); nitrate pool sizes (F). Values are means plus standard errors of the means (SEM) (error bars). Separate two-way ANOVAs were performed on each treatment and are summarized in Table S3 in the supplemental material. Bars with different letters above the bars indicate significant differences at P < 0.05 based on Tukey’s HSD test.