[Multi-year measurement of soil respiration components in a subtropical secondary forest]

A four-year field experiment was performed from March 2010 to February 2014 in order to investigate the contribution of different respiratory components to soil respiration and the temperature sensitivity of different respiratory components. Four blocks were arranged in field, and there were trenched and un-trenched plots in each block. Trenching, which can exclude roots, was performed around the trenched plots. A portable soil CO2 fluxes system ( Li-8100) was used to measure soil respiration rates. Soil temperature and soil moisture were simultaneously observed when measuring soil respiration rates. The results showed that the heterotrophic respiration rate in the trenched plots and the soil respiration rate in the un-trenched plots had the same seasonal pattern. Soil respiration rate in the un-trenched plots was significantly (P < 0.001) higher than that in the trenched plots. Mean soil respiration rates in untrenched plots and mean heterotrophic respiration rate in trenched plots were (2.59 ± 0.48 ) and (1.74 ± 0.28) μmol x (M2 x s)(-1), respectively. There was no significant (P > 0.05) difference in the mean soil respiration rate or mean heterotrophic respiration rate between measurement years. The relationship between heterotrophic respiration and soil respiration could be fitted with a proportion function. Heterotrophic and autotrophic respiration contributed 65.9% and 34.1% to the soil respiration, respectively. The main contributor to soil respiration was heterotrophic respiration. The relationship between the ratio of heterotrophic respiration to soil respiration and measurement date could be fitted with a linear function. An exponential function could be used to fit the relationship between heterotrophic respiration and soil temperature, and between autotrophic respiration and soil temperature. The temperature sensitivity coefficient (Q10) for heterotrophic respiration was lower than that for autotrophic respiration.