Seven-year experimental warming decreases labile but not recalcitrant soil organic carbon fractions in a coastal wetland.

Purpose: The response of soil organic carbon (SOC) fractions to climate warming plays an important role in influencing the fate of soil C stocks. Coastal wetlands have high C sequestration; however, complex water and salt stress conditions lead to a large uncertainty in the effects of warming on SOC dynamics. Further, numerous short-term warming studies cannot provide an unbiased estimate of the warming impacts and mechanisms. Methods: In our study, the topsoil (0–10 cm) and subsoil (20–40 cm) were collected to assess the changes in SOC dynamics after seven-year experiment warming in a coastal wetland in the Yellow River Delta. Additionally, we conducted a short-term dynamic temperature ramping incubation experiment to evaluate the SOC decomposition rate and its temperature sensitivity. Results: Warming significantly decreased the SOC content by 38.7% in the topsoil but had no effect in the subsoil. Warming significantly decreased the labile SOC fractions, including dissolved organic C (DOC) and particulate organic C (POC) in the topsoil but not in the subsoil. By contrast, warming did not alter the recalcitrant mineral-associated organic C (MAOC) fraction in both topsoil and subsoil. Warming-induced elevated soil salinity caused a decrease in labile SOC fractions, presumably through weakening the quantity of plant inputs. In addition, warming significantly increased the SOC mineralization rate in the topsoil, but did not change its temperature sensitivity in both the topsoil and subsoil. Conclusions: Overall, our findings highlight the importance of considering the varying responses of labile and recalcitrant SOC fractions to warming, which would aid in obtaining more accurate projections of SOC dynamics in coastal wetlands under future climate change. [ABSTRACT FROM AUTHOR]