Responses of N2O production and associated functional genes to increasing temperature and moisture in surface and subsurface soils of a temperate forest

Abstract

The effects of increasing temperature and moisture on soil nitrous oxide (N₂O) emissions across different soil horizons remain poorly understood. Here, we investigated how increased temperature (15 °C and 25 °C) and moisture (30 %, 45 %, and 60 % water-filled pore space (WFPS)) influence N₂O emissions from surface (0–5 cm) and subsurface (5–20 cm) soils in a temperate forest. We found that increasing temperature and moisture promoted N₂O production from subsurface soil due to the stimulation of both nitrification- and denitrification-derived N₂O production. However, in surface soil, the effect of increasing temperature on N₂O production is soil moisture dependent, increasing it at 30 % WFPS but decreasing it at 60 % WFPS. This reduction was caused by decreased denitrification-derived N₂O production. Nitrification was identified as the dominant source of N₂O production in both soils, rather than denitrification. Denitrification-derived N₂O production was positively related to nirK gene abundance but not nirS gene abundance, suggesting that nirK-type denitrifiers may be more active than nirS-type denitrifiers. Furthermore, the proportion of nitrified N emitted as N₂O decreased with rising temperature in both soils. Our results underscore the importance of incorporating variable proportions of nitrified N emitted as N₂O in Earth system model to more accurately predict soil N₂O emission in the context of global climate changes.