[Variations of CO2 concentration and δ13C and influencing factors of Quercus variabilis plantation in low hilly area of North China].

The off-axis integrated cavity output spectroscopy technique was used to measure air CO2 concentration and stable carbon isotope ratio (δ13C) above (11 m) and at the bottom (6 m) of canopy of a Quercus variabilis plantation in a low hilly area of North China. The variations of CO2 concentration and δ13C value in Q. variabilis plantation canopy and the influencing factors were analyzed at hourly timescale. The results showed that diurnal variation in the CO2 concentration had a trend, while there was no obvious similar tendency in the diurnal change of δ13C value. Daytime atmosphere stability frequency during the experiment time was 70.2%. With the combined effects of photosynthesis and turbulent in the canopy, CO2 concentration at the bottom of canopy was 1.70 μmol · mol(-1) higher than that above the canopy, while the δ13C value was 0.81 per thousand lower than that above the canopy. Atmosphere stability frequency was 76.2% at night. The CO2 from leaf was not easy to move because of weak turbulent. Thus, CO2 concentration at the bottom of canopy was 1.24 μmol · mol(-1) higher than that above canopy, while the δ13C value was 0.58 per thousand lower than that above canopy. The difference of CO2 concentration between above and at the bottom of the canopy was strongly correlated with their δ13C difference both in daytime and at nighttime. Stepwise regression analysis indicated that solar radiation and relative humidity in daytime were the main environmental factors causing CO2 concentration and δ13C difference between above and at the bottom of the canopy, whereas at nighttime temperature was a key environmental factor influencing δ13C value. The above environmental factors strongly influenced CO2 concentration and δ13C value in air above and at the bottom of Q. variabilis plantation canopy by increasing or decreasing photosynthesis and respiration.