Chin J Plan Ecolo ›› 2007, Vol. 31 ›› Issue (3): 380-385.doi: 10.17521/cjpe.2007.0046

• Research Articles • Previous Articles     Next Articles

EFFECTS OF LINEAR AND EXPONENTIAL FITTING ON THE INITIAL RATE OF CHANGE IN CO2 CONCENTRATION ACROSS THE SOIL SURFACE

WEN Xue-Fa1; SUN Xiao-Min1; LIU Yun-Fen1; LI Xiao-Bo2   

  1. 1Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China; 2 Beijing Ecotek Technology Company Limited, Beijing 100035, China
  • Online:2007-05-30 Published:2007-05-30
  • Contact: WEN Xue-Fa

Abstract:

Aims Soil CO2 flux is driven primarily by the CO2 diffusion gradient across the soil surface. Ideally, the soil CO2 flux measurement should be made without affecting the diffusion gradient across the soil surface. With the closed chamber system, the soil CO2 diffusion rate (əc/ət) is required to estimate the soil CO2 flux. To obtain the əc/ət, the chamber CO2 concentration must be allowed to rise. Consequently, the əc/ət will be affected by the CO2 diffusion gradient across the soil surface because of the decreased CO2 diffusion gradient in the soil chamber. Additionally, the əc/ət will also be affected by the diurnal variation of the CO2 concentration across the soil surface. Our objective was to compare linear and exponential fitting methods to estimate əc/ət.
Methods Currently, the əc/ət are commonly estimated using linear fitting regression. Instead of using the linear fitting method, an exponential fitting method is used to fit the time series of chamber CO2 concentration adopted in the LI-8 100 automated soil CO2 flux system.
Important findings The əc/ətestimated from the linear slopes was consistently underestimated as compared to that from exponential initial slopes. Nighttime əc/ət was significantly negatively correlated with soil surface CO2 concentration, suggesting that the decreased CO2 diffusion gradient across the soil surface strongly influences the əc/ət. For the closed-chamber method, linear curve fitting significantly underestimated the əc/ətrate during the nighttime. These results demonstrated the importance of estimating the əc/ət at ambient soil surface CO2 concentration. The response of the əc/ət to air temperature exhibited significant asymmetry characteristic, showing that it is a better way for exponential fitting to make long-term and continuous soil CO2 flux measurement to elucidate the magnitudes and processes of soil CO2 flux in the typical terrestrial ecosystem.

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