Climate Sensitivities of Carbon Turnover Times in Soil and Vegetation: Understanding Their Effects on Forest Carbon Sequestration

The high uncertainty associated with the response of terrestrial carbon (C) cycle to climate is dominated by ecosystem C turnover time (tau(eco)). Although the relationship between tau(eco) and climate has been extensively studied, significant knowledge gaps remain regarding the differential climate sensitivities of turnover time in major biomass (tau(veg)) and soil (tau(soil)) pools, and their effects on vegetation and soil C sequestration under climate change are poorly understood. Here, we collected multiple time series observations on soil and vegetation C from permanent plots in 10 Chinese forests and used model-data fusion to retrieve key C cycle process parameters that regulate tau(soil) and tau(veg). Our analysis showed that tau(veg) and tau(soil) both decreased with increasing temperature and precipitation, and tau(soil) was more than twice as sensitive (1.27 years/degrees C, 1.70 years/100 mm) than tau(veg) (0.53 years/degrees C, 0.40 years/100 mm). The higher climate sensitivity of tau(soil) caused a more rapid decrease in tau(soil) than in tau(veg) with increasing temperature and precipitation, thereby significantly reducing the difference between tau(soil) and tau(veg) (tau(diff)) under warm and humid conditions. tau(diff), an indicator of the balance between the soil C input and exit rate, was strongly responsible for the variation (more than 50%) in soil C sequestration. Therefore, a smaller tau(diff) under warm and humid conditions suggests a relatively lower contribution from soil C sequestration. This information has strong implications for understanding forest C-climate feedback, predicting forest C sink distributions in soil and vegetation under climate change, and implementing C mitigation policies in forest plantations or soil conservation.

Automated summary

The high uncertainty associated with the response of terrestrial carbon (C) cycle to climate is dominated by the ecosystem C turnover time. The differences in climate sensitivities of turnover time in major biomass and soil pools are poorly understood, and their effects on vegetation and soil C sequestration under climate change remain unclear. This study conducted observations and model-data fusion in Chinese forests to explore the relationship between climate and turnover time. It was found that both vegetation and soil turnover time decreased with increasing temperature and precipitation, and soil turnover time was more sensitive than vegetation turnover time. The smaller balance between soil C input and exit rate under warm and humid conditions suggests a relatively lower contribution from soil C sequestration.