Carbon Dynamics in Natural Grasslands in China

Abstract

China has acknowledged carbon sequestration as a potential mitigation measure for CO2 emissions. Government funded research projects found that grasslands are the second largest carbon sink of the country, indicating their potential to capture large amounts of carbon. However, climate change effects, such as water availability extremities and increased temperatures, affect carbon fluxes that determine carbon sequestration. In an attempt to gain a concise overview of carbon fluxes under the threat of global warming, this study attempted to identify the average strength and direction of the relationships between water availability and temperature, and carbon fluxes. Additionally, it acknowledged the spatial variability of water availability and temperature by addressing whether, and how, the studied relationships differ across grassland types. This study conducted a meta-analysis, including 21 papers which gave 105 regression coefficients as data points. These were used to calculate the average relationships between water availability and GPP, water availability and ecosystem respiration, temperature and GPP and temperature and ecosystem respiration. Additionally, ANOVAs were conducted to identify whether these average relationships differ across grassland types. Key findings from this study have shown that the relationships between water availability and temperature, and carbon fluxes in China grasslands mostly comply with existing knowledge. Overall, positive relationships were identified, and average magnitudes were higher for the relationships between water availability and carbon fluxes, than for the relationships between temperature and carbon fluxes. Surprisingly, the results indicated that grasslands may switch from a carbon sink to a carbon source under conditions of increased water availability. Lastly, differences were found between typical steppes and alpine steppes, with respect to the studied relationships. However, not all differences were significant, and the results were based on few datapoints, limiting this study in some respect. This study has provided insight into the average relationships between water availability and temperature, and carbon fluxes via the means of a meta-analysis. The findings may contribute to environmental decision-making in China, regarding policy design for carbon sequestration as a mitigation measure for CO2 emissions