Spatial and temporal variability of N<sub>2</sub>O emissions in a subtropical forest catchment in China
Subtropical forests in southern 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 (N<sub>2</sub>O). We measured N<su...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2013-03-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/10/1309/2013/bg-10-1309-2013.pdf |
| Summary: | Subtropical forests in southern 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 (N<sub>2</sub>O). We measured N<sub>2</sub>O 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 hillslope (HS) and a hydrologically connected, terraced groundwater discharge zone (GDZ) in the valley bottom. High emission rates of up to 1800 μg N<sub>2</sub>O-N m<sup>−2</sup> h<sup>−1</sup> were recorded on the HS shortly after rain storms during monsoonal summer, whereas emission fluxes during the dry winter season were generally low. Overall, N<sub>2</sub>O emission was lower in GDZ than on HS, rendering the mesic HS the dominant source of N<sub>2</sub>O in this landscape. Temporal variability of N<sub>2</sub>O emissions on HS was largely explained by soil temperature (ST) and moisture, pointing at denitrification as a major process for N removal and N<sub>2</sub>O production. The concentration of nitrate (NO<sub>3</sub><sup>−</sup>) in pore water on HS was high even in the rainy season, apparently never limiting denitrification and N<sub>2</sub>O production. The concentration of NO<sub>3</sub><sup>−</sup> decreased along the terraced GDZ, indicating efficient N removal, but with moderate N<sub>2</sub>O-N loss. The extrapolated annual N<sub>2</sub>O fluxes from soils on HS (0.54 and 0.43 g N<sub>2</sub>O-N m<sup>−2</sup> yr<sup>−1</sup> for a year with a wet and a dry summer, respectively) are among the highest N<sub>2</sub>O fluxes reported from subtropical forests so far. Annual N<sub>2</sub>O-N emissions amounted to 8–10% of the annual atmogenic N deposition, suggesting that forests on acid soils in southern China are an important, hitherto overlooked component of the anthropogenic N<sub>2</sub>O budget. |
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| ISSN: | 1726-4170 1726-4189 |