Stand age amplifies greenhouse gas and NO releases following conversion of rice paddy to tea plantations in subtropical China

Increasing demand of commercial markets for tea products is driving the conversion from rice paddies to tea plantations in subtropical China. So far, however, little is known on how this land-use change, along with the age of plantation establishment, will affect the fluxes of greenhouse gases (GHG) methane (CH4) and nitrous oxide (N2O) and the air-pollutant nitric oxide (NO). Thus, we measured CH4, N2O and NO fluxes over an entire year from two tea plantations (one- and five-year-old plantations) and a native rice-fallow system under two system specific nitrogen fertilizer options. On an annual scale, comparable or higher GHG emissions were measured for tea plantations as compared to the rice-fallow system. Besides the pollution swapping from CH4 being the dominating GHG in rice paddies to N2O in tea plantations, annual NO emissions increased significantly. Annual direct emission factors of N2O and NO in tea plantations were 2.47-5.80% and 2.00-3.99%, respectively, significantly higher than in the rice-fallow system (N2O: 1.05-2.05%; NO: 0.033-0.051%). Differences in N fertilizer inputs and soil environmental conditions (e.g., soil water regime, pH and organic carbon) due to contrasting managements of these systems and their interactions are clearly driving the stimulation of N2O and NO emissions and contributing to the significant CH4 reductions. Furthermore, we observed that increasing tea stand age, particularly under organic fertilization, further stimulated N2O and NO emissions that varied significantly intraannually. Nevertheless, the higher N2O and NO emissions of tea plantations and the increasing emission strength with stand age deserve further research attention and consideration for future land-use conversions.