Scale effect of climate on soil organic carbon in the Uplands of Northeast China

Purpose: Climate factors, considered significant factors in regulating soil organic carbon (SOC), are not equally important at all spatial scales. However, the scale which provides the optimal relationship between climate and SOC and how that relationship varies at multiple scales are still unclear. Thus, it is crucial to study the relationship between climate factors and SOC at multiple scales when attempting to accurately predict the SOC pool and evaluate the influence of climate change on global carbon cycling. The objective of this research is to examine the scale effect of climate factors on SOC content in the Uplands of Northeast China. Materials and methods: The relationship between climate factors and SOC content at the regional, provincial, city, and county scales was evaluated at 0-20 and 0-100 cm using correlation and regression analysis. Data for the study in the Uplands of Northeast China were examined using 1,022 profiles obtained from the Second National Soil Survey of China. A nested sampling scheme was adopted at four scales for this research. Results and discussion: Differences exist in the degree of correlation and relative importance of temperature and precipitation at different scales. Temperature is the main climate factor controlling SOC content at the regional scale. At the provincial scale, temperature is also the main climate factor controlling SOC content in the Uplands of Heilongjiang and Eastern Inner Mongolia. SOC content in Jilin and Liaoning is influenced jointly by temperature and precipitation. Additionally, obvious regional differences occurred in the relationship between climate factors and SOC content at the provincial scale. Although this scale differs from those by other researchers, similar results have been reported in China, Spain, and the USA. The reasons might be attributed to the differences in soil type, ecosystem, and topographic position. At both the city and county scales, weak or no relation was observed between climate factors and SOC content. Climate factors have limited ability to explain SOC content variability given that SOC is affected by multiple factors which were not taken into account by this research. Therefore, multiple scales should be considered when the feedback relationship between global climate change and SOC content is studied. Conclusions: The relationship between climate factors and SOC content weakens with decreasing scale, especially from the provincial to city scale. The main climate factors controlling SOC content vary with different scales. The provincial scale is optimal for studying the relationship between climate factors and SOC content in the Uplands of Northeast China. Recommendations and perspectives: Seasonal change of temperature and precipitation may also influence SOC. Thus, it is necessary to consider climate factors at multiple timescales. Moreover, further studies focusing on the scale effect of other factors (including climate) on SOC content variability will be carried out at different scales to determine the main factors controlling SOC content.