Spatial and temporal variability of N<sub>2</sub>O emissions in a subtropical forest catchment in China

Abstract

Subtropical forests in South China have received chronically large amounts of atmogenic nitrogen (N) causing N saturation. Recent studies suggest that a significant proportion of the N input is returned to the atmosphere, in part as nitrous oxide (N₂O). We measured N₂O emission fluxes by closed chamber technique throughout two years in a Masson pine-dominated headwater catchment with acrisols (pH ~ 4) at TieShanPing (Chongqing, SW China) and assessed the spatial and temporal variability in two landscape elements typical for this region: a mesic forested hill slope (HS) and a hydrologically connected, terraced groundwater discharge zone (GDZ) in the valley bottom. High emission rates of up to 1800 μg N₂O-N m⁻² h⁻¹ were recorded on the HS shortly after rain storms during monsoonal summer, whereas emission fluxes during the dry winter season were generally low. Overall, N₂O emission was lower in GDZ than in HS, rendering the mesic HS the dominant source of N₂O in this landscape. Temporal variability of N₂O emissions on HS was largely explained by soil temperature and moisture, pointing at denitrification as a major process for N removal and N₂O production. The concentration of nitrate (NO₃^−) in pore water on HS was high even in the rainy season, apparently never limiting denitrification and N₂O production. The concentration of NO₃^− decreased along the terraced GDZ, indicating efficient N removal, but with moderate N₂O-N loss. The extrapolated annual N₂O fluxes from soils on HS (0.50 and 0.41 g N₂O-N m⁻² yr⁻¹ for a year with a wet and a dry summer, respectively) are among the highest N₂O fluxes reported from subtropical forests so far. Annual N₂O-N emissions amounted to 8–10% of the annual atmogenic N-deposition, suggesting that forests on acid soils in South China are an important, hitherto overlooked component of the anthropogenic N₂O budget

Responses of nitrous oxide emissions to nitrogen and phosphorus additions in two tropical plantations with N-fixing vs. non-N-fixing tree species

“…The rates of N 2 O emission observed from the controls of AA and EU plantations (1.9 to 2.3 kg N 2 O-N ha −1 yr −1 ) are comparable with previous reports in (sub)tropical regions of southern China (2.0 to 4.8 kg N 2 O-N ha −1 yr −1 ) (Zhang et al, 2008;Zhu et al, 2013a), and also within the range of published results (1.2-2.6 kg N 2 O-N ha −1 yr −1 ) from other tropical forests (Werner et al, 2007;Gharahi Ghehi et al, 2012). Higher rates of N 2 O emissions (3.7-7.5 kg N 2 O-N ha −1 yr −1 ) than our study were also reported from tropical forests (Keller and Reiners, 1994;Kiese and ButterbachBahl, 2002).…”

“…In the study, N 2 O fluxes showed positive linear relationships with soil temperatures and WFPS, which were consistent with tropical and subtropical forests (Butterbach-Bahl et al, 2004;Zhang et al, 2008;Zhu et al, 2013a). There is a covariation between soil temperature and WFPS in the monsoon climate zone of southern China.…”

Nitrogen and phosphorus addition impact soil N2O emission in a secondary tropical forest of South China

“…This secondary tropical forest in wet seasons thus has favorable conditions for denitrification to emit considerable amounts of N 2 O, i.e., low oxygen content due to high water-filled pore-space (WFPS) and temperature high enough to allow microbial activity to occur. In some tropical and subtropical forests, denitrification contributed more than 70% of soil N 2 O emission43. In the present study, the SEM shows that soil NO 3 − was significantly associated with soil N 2 O emission, and the model totally explained 58% of the variation of soil N 2 O emission in wet seasons.…”

Humid Subtropical Forests Constitute a Net Methane Source: A Catchment‐Scale Study

“…The TSP catchment is mainly composed of hillslopes, characterized by well‐drained soils (Haplic Acrisol; WRB, ; Zhu et al, ). Water interflow over the argic horizon (which has a high clay content typical for Acrisols) on the hillslope is laterally discharged into the terraced valley bottom of the catchment, where soils are mainly Cambisols (WRB, ) with low hydraulic conductivity.…”

“…In the present study, we quantify CH 4 fluxes weekly to biweekly in a subtropical, N‐saturated forested catchment (Tieshanping, TSP) in SW China over a 3‐year period, including wet and dry summers. The catchment mainly consists of hillslopes with well‐drained soils, where interflow over the argic horizon is laterally transferred to a small area in the valley bottom (groundwater discharge zone), resulting in water saturation following intensive rain episodes (Zhu et al, ). Sampling was conducted along a topographic gradient at four landscape elements, including hillslope, foot of the hillslope, valley bottom, and groundwater discharge zone.…”