Monsoon rains, drought periods and soil texture as drivers of soil N2O fluxes – Soil drought turns East Asian temperate deciduous forest soils into temporary and unexpectedly persistent N2O sinks

To quantify N2O fluxes between soil and atmosphere and understanding those processes driving them, is crucial if we aim to reliably predict one of earthʹs important greenhouse gasesʹ origin and fate. Soil moisture has been identified as one major driver of N2O fluxes, drought has been observed to decrease soil N2O emissions and accounts for soil N2O consumption. We monitored N2O fluxes occurring at the soil/atmosphere interface of three temperate deciduous Korean forest sites experiencing a pronounced early summer drought followed by heavy East Asian monsoon rains. Because soil texture can enhance or mitigate soil drought effects, we selected sites which were different in topsoil texture. Therefore, we took closed chamber measurements of N2O fluxes during the growing season 2010 and determined N2O concentrations and δ15N values along soil profiles in the dry and monsoon season for a sandy-loam site. We observed N2O consumption at all of our study sites during early summer drought, which turned into N2O emission during the monsoon season. The N2O balance of the sandy-loam site remained slightly negative during the entire vegetation period. Soil moisture explained most of the measured N2O fluxes. For a sandy-loam forest soil we calculated a switch between N2O emission and consumption at an intermediate soil moisture (pF level of 3.02) which corresponds to a water filled pore space (WFPS) of 36%, but at half an order of magnitude moister soil (pF level: 2.57; WFPS 50%) at a loamy site. N2O concentration and δ 15 N N 2 O values along the soil profiles suggest that those processes driving the N2O fluxes at the soil/atmosphere interface most likely occurred in the topsoil. Our results contribute to our knowledge on the global N2O budget, because monsoon affected forests cover large areas worldwide and their soilsʹ N2O emissions have so far been uninvestigated.