Abstract
Abstract. 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 (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 hillslope (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 on 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 (ST) 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 (0.54 and 0.43 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 southern China are an important, hitherto overlooked component of the anthropogenic N2O budget.
Highlights
Earth System SciencesThe global atmospheric concentration of nitrous oxide (N2O), an important greenhouse gas and decomposer of stratospheric ozone, has increased from a pre-industrial level of 270 ppbv to 322 ppbOv cine2a00n8 S(WcMieOn, c20e09)
N2O emission rates recorded after the heavy rainstorm in 2009 are the highest found for forest ecosystems so far and exceed rates reported fortropical forests which typically vary between 11 to 600 μg N2O-N m−2 h−1 (Liu et al, 2011a; Zhang et al, 2008; Silver et al, 2005; Ishizuka et al, 2005; Koehler et al, 2009; Rowlings et al, 2012; Kiese and Butterbach-Bahl, 2002)
Large smallscale spatial variability of N2O emissions is often reported for forest soils (Robertson and Klemedtsson, 1996; Bowden et al, 1992; Werner et al, 2007b) and is commonly attributed to small-scale variation in mineral N availability, litter quality and soil moisture
Summary
Earth System SciencesThe global atmospheric concentration of nitrous oxide (N2O), an important greenhouse gas and decomposer of stratospheric ozone, has increased from a pre-industrial level of 270 ppbv to 322 ppbOv cine2a00n8 S(WcMieOn, c20e09). The global source strength is estimated to be 17.7 Tg N yr−1, with agriculture contributing 2.8 (1.7–4.8) Tg N yr−1 and soils under natural vegetation 6.6 (3.3–9.0) Tg N yr−1 (IPCC, 2007; Hirsch et al, 2006). Both estimates based on bottom-up approaches (Stehfest and Bouwman, 2006) and on observations of the N2O atmospheric columSno(KlidortEetaalr.,th2011; D’Amelio et al, 2009; Hirsch et al, 2006) suggest that 50–64 % of the atmospheric N2O derive from the (sub)tropical zone 0◦ to 30◦ N. Large parts of southern China are situated in the humid subtropics and the dominant forest types are evergreen broadleaf and coniferous forest, many of which are found as patches in densely populated areas with intensive agriculture.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
