Temporal patterns of carbon-water coupling of a subalpine peatland in subtropics: Insights from a seven-year eddy covariance monitoring

Study region: A well-preserved subalpine peatland in the subtropics, the Dajiuhu peatland, in Shennongjia, Hubei Province, China. Study focus: Over a seven-year period, constant in-situ carbon flux monitoring was conducted using the eddy covariance method. The patterns of CO2 and H2O fluxes were analyzed, encompassing both daytime and nocturnal period observations, spanning both growing and non-growing seasons, and the interconnection between carbon and water within the Dajiuhu peatland. Furthermore, this investigation identified meteorological parameters shaping these flux dynamics. New hydrological insights for the region: The water source function was more resilient to the effects of extreme weather events and showed higher stability when compared to the carbon sink function. Daytime carbon-water coupling presented a pronounced negative correlation during the growing season, contrasting with a more complex trinomial relationship evident during the non-growing season; however, nocturnal periods did not reveal any apparent correlation. Relative humidity (RH), water table depth (WTD), and evapotranspiration (ET) emerged as key variables impacting jointly on both CO2 and H2O fluxes. Furthermore, net radiation (Rn) magnifies the hysteresis loops associated with net ecosystem exchanges of CO2 (NEE) during the growing season, with WTD being the prime determinant influencing seasonal fluctuations in hysteresis related to H2O fluxes. These findings exemplify the complexities inherent in the management of carbon and water resources within subalpine peatlands, underscored by their intricately intertwined and inseparable relationship.