THE EFFECT OF TEMPERATURE AND NH3 CONCENTRATION ON NH3 OXIDISING ARCHAEA AND BACTERIA IN AGRICULTURAL SOIL

The aim of this study was to study the effect of temperature and NH4+concentration on NH4+oxidising activity and community structures of bacterial and archaeal NH4+oxidisers in Scottish soil. Microcosms were amended with low and high NH4+ concentration and incubated at five different temperatures (15, 20, 25, 30 and 35oC) for 28 days. Nitrification activity, AOA and AOB growth increased with temperature and AOB growth were greatest at 30oC in microcosms incubated with high NH4+ concentration, while AOA growth was detected, irrespective of soil NH4+ concentration and at all incubation temperature except 35oC. AOB growth was detected at 35oC even in microcosms incubated with low NH4+ concentration. There was a greater change in the community structure of AOA and AOB with an increase in temperature only. This probably suggests that NH4+ oxidation was dominated by AOA at low concentration between 15 - 30 oC and at 35 oC AOB were able to grow when the competition with AOA for NH4+ in soil was relieved by high temperature (35 oC) that inhibited AOA growth. The differences in AOA and AOB responses to temperature could suggest an additional niche differentiating factor between AOA and AOB. Temperature but not NH4+ is one of the key environmental factors responsible for changes in the relative abundance and community structure of AOA and AOB in soil.