Simulated nitrogen inputs influence methane and nitrous oxide fluxes from a young larch plantation in northern Japan

초록

Future increases in nitrogen (N) deposition have the potential to change underground nutrient dynamics in forest ecosystems and alter the soil-atmosphere exchange of greenhouse gases (GHGs), such as methane (CH4) and nitrous oxide (N2O). To clarify changes in soil CH4 and N2O fluxes following N application, N input was initiated at the onset of our experiment and included two treatments (0 and 50 kg N m(-2) yr(-1)) with four replicates in a young larch plantation in northern Japan. The N was added as an ammonium nitrate (NH4NO3) solution and distributed four times per year during two growing seasons. Soil GHG fluxes and soil variables were determined on ten occasions during a period that spanned the two growing seasons. Before the N application, no significant differences were observed in any of the soil variables between the two treatments. Ammonium-N (NH4-N) and nitrate-N (NO3-N) concentrations increased immediately after N applications in the 50 kg-N addition plot. With an increasing pool of inorganic-N, we found that soil CH4 uptake in the 50 kg-N addition plot decreased by 48% when compared to the Zero-N control plot. In particular, reduced CH4 uptake or CH4 emissions were observed in 50 kg-N addition soils immediately after N input events. Moreover, N inputs increased soil N2O emissions by an average of 69% in the 50 kg-N addition plot compared to the control during two growing seasons. At this experimental site, a negative spatial relationship was observed between soil CH4 uptake and the NH4-N concentration, and a positive spatial relationship was seen between soil N2O emissions and the NO3-N concentration, despite high inherent spatial variability in the soil CH4 flux. Overall, these results suggest that N deposition-induced increases in the availability of inorganic-N in the soil may affect processes linked to CH4 and N2O dynamics in cool-temperate forest soils, at least over the short term. (C) 2011 Elsevier Ltd. All rights reserved.

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