| 摘 要： |
Soil carbon dioxide (CO2) efflux (F-s) and its carbon isotopic composition (delta(Fs)) based on the chamber methods are widely used to represent soil respiration and its carbon isotopic signature. However, the effects of diffusive transport-induced fractionation and measured random errors of the chamber system on the capture of diel delta(Fs), especially at a low F-s, remain unidentified. We aimed to investigate the did variations in delta(Fs) and improve the mechanistic understanding of delta F-s using the chamber methods. We developed a multi-chamber system with a Picarro carbon isotopic analyzer to measure did F-s and delta(Fs) in a subtropical plantation and conducted flux tests to verify the performance of our chamber system beforehand. The did delta(Fs) variations were disentangled with support from a non-steady state diffusion (NSS) model. There were no remarkable systematic errors using our chamber system, F-s was clear with a did amplitude< 4 mu mol M-2 s(-1), but delta(Fs) showed no did variation when random errors were greater than similar to 2 parts per thousand. The NSS model results showed that did trends of modeled delta(Fs) were highest in the morning and lowest in the afternoon, and the diffusive fractionation had a profound effect on the delta(Fs) variations, especially when F-s was low. Flux simulation tests and in situ measurements showed that measured random errors in delta(Fs) increased exponentially with decreasing F-s. The did variations in delta(Fs) might not be disentangled at low F-s when its random errors were beyond the amplitude of did delta(Fs) and were aggravated by the effects of diffusive fractionation. |
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