Dynamics and underlying mechanisms of NO and NO emissions in response to a transient land-use conversion of Masson pine forest to tea field.

Nowadays, there has been a rapid expansion of tea field converted from forestry for pursuing higher economic benefits. However, few researches focus on the effects of transient land-use conversion from Masson pine forest to artificial tea fields on soil NO and NO emissions and the underlying mechanisms. A parallel field experiment was conducted from Masson pine forest and a newly converted tea plantation from Masson pine forest from 2013 to 2017 in subtropical central China. Masson pine forest conversion to tea field dramatically increased soil NO and NO emissions (up to 4.00 ± 0.43 and 1.93 ± 0.45 kg N ha yr, respectively) in the first year possibly due to enhanced soil organic N mineralization. With the extension of tea planting age, NO and NO emissions showed an upward trend (ranged from 1.19 to 5.28, and 0.15 to 1.78 kg N ha yr, respectively) influenced by fertilization and soil organic matter accumulation. The direct emission factors for NO and NO in the newly converted tea fields were the largest in the first year (2.64 and 1.07%, respectively) after land-use conversion, and higher than the default value recommended by IPCC. The NO/NO ratio was mainly lower than 1 in the fertilized tea field, and soil NO and NO emission peaks mainly occurred in tea-growing season (wet season) with higher soil moisture and NH-N concentrations, and dominated by amoA-containing bacteria (AOB), suggesting nitrifier-denitrification could be the dominant process involved in soil nitrogenous gases emissions in tea field. These results can be summarized as dramatically increased soil NO and NO emissions during the transient land-use conversion from Masson pine forest to tea field were possibly due to the substantial net soil organic N mineralization and the enhanced abundance of nitrification functional genes (AOB).