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

Abstract To quantify N 2 O fluxes between soil and atmosphere and understanding those processes driving them, is crucial if we aim to reliably predict one of earth's important greenhouse gases' origin and fate. Soil moisture has been identified as one major driver of N 2 O fluxes, drought has been observed to decrease soil N 2 O emissions and accounts for soil N 2 O consumption. We monitored N 2 O 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 N 2 O fluxes during the growing season 2010 and determined N 2 O concentrations and δ 15 N values along soil profiles in the dry and monsoon season for a sandy-loam site. We observed N 2 O consumption at all of our study sites during early summer drought, which turned into N 2 O emission during the monsoon season. The N 2 O balance of the sandy-loam site remained slightly negative during the entire vegetation period. Soil moisture explained most of the measured N 2 O fluxes. For a sandy-loam forest soil we calculated a switch between N 2 O 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. N 2 O concentration and δ 15 N N 2 O values along the soil profiles suggest that those processes driving the N 2 O fluxes at the soil/atmosphere interface most likely occurred in the topsoil. Our results contribute to our knowledge on the global N 2 O budget, because monsoon affected forests cover large areas worldwide and their soils' N 2 O emissions have so far been uninvestigated.