Exposure of mineral soils to atmospherically relevant concentrations of (13)CH(4) (2 ppmv) followed by (13)C-phospholipid fatty acid stable isotope probing allows assessment of the high-affinity methanotrophic bacterial sink in hitherto unattainable detail. Utilizing this approach, inorganic fertilizer-treated soils from a long-term agricultural experiment were shown to display dramatic reduction, by > 70%, of the methanotrophic bacterial cell numbers. Reduction in the methane sink capacity of the soils was slightly lower than the directly observed reduction in methanotrophic bacterial counts, indicating that the inhibitory effects on high-affinity methanotrophic bacteria are not fully expressed through CH(4) oxidation rates. The results emphasize the need to rigorously assess commonly applied agricultural practices with respect to their unseen negative impacts on soil microbial diversity in relation to terrestrial sinks for atmospheric trace gases.