Population Size of Ammonia-Oxidizing Bacteria in Soil Trench Systems

Abstract

The nitrogen removal mechanism of soil trench systems is considered to involve coupling of nitrification and denitrification in different soil layers; however, the distribution and population sizes of the nitrifying and denitrifying bacteria present in it have not been clarified. The primary objective of this research was to spatially quantify the population size of ammonia-oxidizing bacteria (AOB) in a soil trench system in Sasagi (Tsukuba, Japan) by using potential nitrification activity and the real-time PCR method. From the potential nitrification activity analysis, it was found that nitrification occurred predominantly in the depths above 40 cm and decreased with an increase in the depth except at the 10-cm depth. AOB were found at all depths by real-time PCR except at the depths of 50 cm and 60 cm, which was explained by the very low saturated conductivity and high bulk density unsuitable for the growth of AOB. At depths above 40 cm, the AOB population size estimated by potential nitrification activity and the real-time PCR method had nearly the same tendency to decrease with an increase in the depth except at the 10-cm depth. The vertical distribution of the total bacteria was also estimated by real-time PCR. Moreover, the population sizes of AOB and total bacteria increased near and below the depth of 70 cm where influent flows in.