Regulating effects of climate, net primary productivity, and nitrogen on carbon sequestration rates in temperate wetlands, Northeast China

Temperate wetlands in the Northern Hemisphere have high long-term carbon sequestration rates, and play critical roles in mitigating regional and global atmospheric CO2 increases at the century timescale. We measured soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) from 11 typical freshwater wetlands (Heilongjiang Province) and one saline wetland (Jilin Province) in Northeast China, and estimated carbon sequestration rates using 210Pb and 137Cs dating technology. Effects of climate, net primary productivity, and nutrient availability on carbon sequestration rates (Rcarbon) were also evaluated. Chronological results showed that surface soil within the 0-40 cm depth formed during the past 70-205 years. Soil accretion rates ranged from 2.20 to 5.83 mm yr−1, with an average of 3.84 ± 1.25 mm yr−1 (mean ± SD). Rcarbon ranged from 61.60 to 318.5 gC m−2 yr−1 and was significantly different among wetland types. Average Rcarbon was 202.7 gC m−2 yr−1 in the freshwater wetlands and 61.6 gC m−2 yr−1 in the saline marsh. About 1.04 × 108 tons of carbon was estimated to be captured by temperate wetland soils annually in Heilongjiang Province (in the scope of 45.381-51.085°N, 125.132-132.324°E). Correlation analysis showed little impact of net primary productivity (NPP) and soil nutrient contents on Rcarbon, whereas climate, specifically the combined dynamics of temperature and precipitation, was the predominant factor affecting Rcarbon. The negative relationship observed between Rcarbon and annual mean temperature (T) indicates that warming in Northeast China could reduce Rcarbon. Significant positive relationships were observed between annual precipitation (P), the hydrothermal coefficient (defined as P/AT, where AT was accumulative temperature ≥10 °C), and Rcarbon, indicating that a cold, humid climate would enhance Rcarbon. Current climate change in Northeast China, characterized by warming and drought, may form positive feedbacks with Rcarbon in temperate wetlands and accelerate carbon loss from wetland soils.