Quantifying soil nitrous oxide emissions in spring freezing-thawing period over different vegetation types in Northeast China

Environmental changes significantly alter the structure, diversity and activity of soil microbial communities during spring freezing-thawing period, leading to changes in the soil microbial nitrogen cycle. Changes in N₂O fluxes after land use conversion from primary forest to secondary forest, Korean pine plantation and cropland in northeast China have not been quantified. Field experiments were conducted to measure soil N₂O fluxes in a primary forest, two secondary forests, a Korean pine plantation, and one maize field in a temperate region in northeast China from 2017-03-06 to 2017-05-28. During the experimental period, the soil was exclusively a nitrogen source for all land uses. We found that N₂O emissions ranged from 15.63 to 68.74 μg m⁻² h⁻¹, and cumulative N₂O emissions ranged from 0.33 to 2.10 kg ha⁻¹ during the period. Cumulative N₂O emissions from the maize field were significantly higher than that from primary forest, Korean pine plantation, hardwood forest, and Betula platyphylla forest by 262.1% to 536.4%. Compared with other ecosystems in similar studies, the N₂O emission rates of all ecosystem types in this study were low during the spring thaw period. Stepwise multiple linear regression indicated that there were significant correlations between N₂O emissions and environmental factors (air temperature and soil temperature, soil water content, soil pH, NH₄⁺-N, NO₃⁻-N, and soil organic carbon). The results showed that conversion of land use from primary forest to hardwood forest, Korean pine plantation or maize field greatly increased soil N₂O emissions during spring freezing-thawing period, and N₂O emissions from primary forest were almost the same as those from Betula platyphylla forest.