Characterization of Soil Respiration in a Shrubland Ecosystem of Artemisia ordosica in Mu Us Desert; [毛乌素沙地油蒿灌丛生态系统的土壤呼吸特征]

Objective: We investigated the characteristic of soil respiration rate and its responses to soil temperature and soil moisture in a shrubland ecosystem in Mu Us Desert to provide a scientifics basis for predicting soil carbon emission in semiarid region. Method: The trench method has used in a typical Artemisia ordosica community in Yanchi County to separate the components of soil respiration. Using an automated chamber system, soil respiration rate was measured continuously from April to October 2014 in both trenched and control plots. An exponential function was used to fit the relationship between soil respiration rates and soil temperature (Ts), and a linear regression was used to test the relationship between soil water content (SWC) and temperature normalized soil respiration rates (the ratio of observed values to estimated values). Result: At the diurnal scale, autotrophic respiration ratio (RA) showed a middy depression, and reached the peak value earlier (11:00) than Ts (15:00), while heterotrophic respiration ratio (RH)peaked in consistent with Ts. During mid-growing season (Jun-Aug), the temperature sensitivity (Q10) of total soil respiration ratio (RT), RA and RH was 1.51, 1.40, and 1.88, respectively. However, the response of RA to Ts was modified by SWC. When SWC < 8%, Ts explained only 36% of the variation in RA (Q10=1.10) and temperature normalized RA showed a significant linear relationship with SWC. When SWC > 8%, RA increased exponentially with increasing Ts (R2 =0.75,Q10 =1.88), and there was no significant relationship between temperature normalized RA and SWC. In contrast to RA, SWC had little effect on the relationship between RH and temperature, RHincreased exponentially with increase of Ts under different water conditions (R2 > 0.65). The contribution of RA to RT (RA/RT) showed a middy depression at diurnal scale. At the seasonal scale, RA/RT showed clear seasonal variation. RA/RT averaged 54% during May-Aug and was higher (69%) during Sep-Oct. Conclusion: At the diurnal scale, RA was decoupled from Ts, while RH was primarily controlled by Ts. At the seasonal scale, RH was primarily controlled by Ts with a higher Q10 than that of RA. However, the response of RA to Ts was regulated by SWC. The variations in RA/RT at diurnal and seasonal scales are most likely derived from the different responses of RA and RH to environmental factors. Our result could help understand the dynamics in soil respiration and provided a scientific basis for predicting carbon budget in semiarid regions. © 2018, Editorial Department of Scientia Silvae Sinicae. All right reserved.