Liming enhances the abundance and stability of nitrogen-cycling microbes: the buffering effect of long-term lime application

Lime application (liming) has historically been used to ameliorate soil acidity in grasslands. Liming effectively improves soil pH, plant productivity, and soil physicochemical properties, but the long-term impact of acidity control by liming on key microbial nitrogen (N)-cycling genes in semi-natural grasslands is unknown. We investigated the effect of 65 years of liming on N-cycling processes in the limed and control plots of the Ossekampen long-term grassland experiment in the Netherlands. These plots have not received any other fertilizers for 65 years. Soil sampling and nitrous oxide (N₂O) emission measurements were conducted three times in spring and four times in summer, and quantitative real-time PCR was performed to determine the absolute abundances of N-cycling genes, including ammonia-oxidation (amoA-AOB, amoA-AOA, amoA-comammox), denitrification (nirS, nirK, nosZ), nitrate ammonification (nrfA), and N-fixation (nifH) genes. Long-term liming increased the absolute abundances of nitrifiers, denitrifiers, and nitrate ammonifiers. Soil N₂O emissions did not differ significantly between liming and control treatments. Additionally, liming had a buffering effect that maintained the population of N-cycling microbes against seasonal variations in abundance. Our results indicate that improving soil acidity through liming potentially facilitates microbial N-cycling processes without increasing N₂O emissions.