Carbon Source/Sink Dynamics and Trend of Larix chinensis in Northern Slope of Qinling Mountains Based on BIOME-BGC Model

Abstract:

Climate change and elevated CO₂ concentration affect productivity and carbon balance of forest ecosystems. Timberline tree, Larix chinensis is extremely sensitive to climate change. In order to understand the carbon source/sink dynamics, the BIOME-BGC model was used to simulate the productivity, carbon storage and carbon use efficiency (CUE) of Larix chinensis in the northern slope of Qinling Mountains during 1959-2016, and the future trend of carbon source/sink function was projected by climate scenario setting method. The results showed that in the past 58 years, the average NPP, GPP and NEP were 328.59, 501.56 and 31.42 g C m^-2a^-1, respectively. The average carbon storage was 35.38 kg C m^-2a^-1, and the average CUE was 0.65. Except that 1960-1961, 1969-1970 and 1997-1999 were "carbon source" years, the rest were "carbon sink" years, showing the characteristics of "carbon source-carbon sink-carbon source" during the whole year. Overall, carbon storage increased and the potential carbon sequestration capacity was relatively stable. The positive effects of GPP, NPP and carbon storage were in the order of temperature increment > CO₂ concentration enhancement, while the opposite effect of NEP had adverse order. Rainfall enhancement had counteraction on productivity and carbon storage, and temperature increment had a negative effect on CUE. Temperature and CO₂ concentration were the limiting factors for the growth of L. chinensis in northern slope of Qinling Mountains, and the limitation of temperature was stronger than that of CO₂ concentration. In the future, the increase of temperature or CO₂ concentration will benefit the function of carbon sink, and the increase of precipitation will weaken the effect of carbon sink. In the RCP4.5 and RCP8.5 scenarios, the productivity and carbon storage of L. chinensis showed an upward trend in 21 century, and RCP8.5 increased slightly more than RCP4.5. The potential carbon sequestration capacity was still strong. January to March, October to December would be "carbon source" month, and May to September would be "carbon sink" month. These revealed the effects of temperature, precipitation and CO₂ concentration on carbon source/sink of L. chinensis under the background of climate change. The increase of temperature and CO₂ concentration were the promoting factor for carbon sink of L. chinensis, while the increase of precipitation was the limiting factor.