Effect of carbon and nitrogen addition on nitrous oxide flux from temperate forest soils under different wetting intensity conditions

Packed soil-core incubation experiments were done to study the effects of carbon (glucose, 6.4 g Cm?2) and nitrogen (NH₄Cl and KNO₃, 4.5 g N m?2) addition on nitrous oxide (N₂O) fluxes from a mature broadleaf and Korean pine mixed forest (BKPF) soil and adjacent white birch forest (WBF) soil under two wetting intensities (55% and 80% WFPS). The results showed that with the except of the WBF soil added with NH₄Cl alone under high wetting intensity, increased wetting intensity and addition of carbon and nitrogen could significantly enhance N₂O fluxes from the two forest soils, singly and interactively (P<0.05). Glucose-induced N₂O fluxes from BKPF and WBF soils were 0.53-2.67 and 4.70-29.32 mg N₂O-N m?2, respectively, especially under high wetting conditions and from the WBF soil, which coincided with a significant decrease in soil inorganic N concentration, especially for the water-extractable NO₃? in the WBF soil under high wetting conditions. These illustrated that stimulating effect of glucose addition on the soil N₂O fluxes increased with increasing wetting intensity, particularly for the WBF soil. Under low wetting conditions, stimulating effect of glucose addition on the N₂O fluxes was partly inhibited by extraneous N addition during early stage of the incubation, and then it altered with types of forest vegetation and the N pools added. However, under high wetting conditions, stimulating effect of glucose was enhanced by N addition, particularly by KNO₃addition (P<0.05). Additionally, glucose addition could significantly increase microbial biomass carbon and the ratios of microbial biomass carbon to nitrogen in the both forest soils, thus suggesting the change in microorganism communities. Nitrogen addition of two types increased concentrations of water- and K₂SO₄-extractable DON in both soils, especially in BKPF soil, and there were no differences between the two types of N added. Stepwise regression analysis showed that 61% of the variability in the N₂O flux from WBF soil could be attributed to concentrations of WFPS, water-extractable NH₄⁺-N and DON and the ratio of microbial biomass carbon to nitrogen and influenced by the water-extractable DON mostly. Meanwhile, 50% of the variability in the N₂O flux from BKPF soil could be explained by the concentration of WFPS, the water-extractable NH₄⁺-N and microbial biomass carbon and influenced by WFPS mostly. From the results, it can be concluded that wetting-induced N₂O fluxes from temperate forest soils could be related to wetting intensity, microbial biomass and available N pools in soils.