Enhanced soil potential N2O emissions by land-use change are linked to AOB-amoA and nirK gene abundances and denitrifying enzyme activity in subtropics

Conversion of forestland to intensively managed agricultural land occurs worldwide and can increase soil nitrous oxide (N2O) emissions by altering the transformation processes of nitrogen (N) cycling related microbes and environmental conditions. However, little research has been conducted to assess the relationships between nitrifying and denitrifying functional genes and enzyme activities, the altered soil environment and N2O emissions under forest conversion in subtropical China. Here, we investigated the long-term (two decades) effect of converting natural forests to intensively managed tea (Camellia sinensis L.) plantations on soil potential N2O emissions, inorganic N concentrations, functional gene abundances of nitrifying and denitrifying bacteria, as well as nitrifying and denitrifying enzyme activities in subtropical China. The conversion significantly increased soil potential N2O emissions, which were regulated directly by increased denitrifying enzyme activity (52 %) and nirS + nirK gene abundance (38 %) as shown by structural equation modeling, and indirectly by AOB-amoA gene abundance and inorganic N concentration. Our results indicate that converting natural forests to tea plantations directly increases soil inorganic N concentration, resulting in increases in the abundance of soil nitrifying and denitrifying microorganisms and the associated N2O emissions. These findings are crucial for disentangling the factors that directly and indirectly affect soil potential N2O emissions respond to the conversion of forest to tea plantation.