Responses of soil ammonia oxidation and ammonia-oxidizing communities to land-use conversion and fertilization in an acidic red soil of southern China

Abstract

Ammonia oxidation, the conversion of ammonium (NH4+-N) to nitrite (NO2−-N), is the critical step of nitrification and performed by ammonia-oxidizing archaea (AOA) and bacteria (AOB). However, the effects of land-use conversion and fertilization on the AOA and AOB are not well documented, and the contribution of these two groups to soil ammonia oxidation is still debatable. This study aimed to explore how land-use conversion from rice paddies (RP) to citrus orchards (OR) and fertilization affect the abundance and communities of AOA and AOB, and whether AOA and AOB were correlated to ammonia oxidation. The potential ammonia oxidation (PAO) was measured by chlorate inhibition method, and the abundance and communities of AOA and AOB were quantified using quantitative real-time polymerase chain reaction (qPCR), terminal restriction fragment length polymorphism (T-RFLP) and cloning and sequence analysis. Land-use conversion from RP to OR tended to increase PAO, whereas fertilization increased PAO only in the OR. qPCR results demonstrated that land-use conversion significantly increased AOA abundance, but failed to affect the AOB abundance. The AOA abundance was increased in the OR but decreased in the RP after fertilization, whereas fertilization distinctly stimulated AOB abundance in the OR and RP. T-RFLP analysis showed that the communities of AOA and AOB were significantly changed after land-use conversion. Meanwhile, fertilization significantly affected the communities of AOB both in the OR and RP and only affected the communities of AOA in the OR. Phylogenetic analyses of amoA genes showed that group 1.1 a like lineage predominated archaea ammonia oxidizers in the acidic red soil, while all AOB clones were belonged to the Nitrosospira. Besides, soil ammonia oxidation was positively correlated to AOA and AOB abundance both in the OR and RP. Our findings imply that land-use conversion and fertilization could potentially alter the ammonia oxidation by regulating the growth of AOA and AOB in this acidic red soil.