Forest Soil Profile Inversion and Mixing Change the Vertical Stratification of Soil CO₂ Concentration without Altering Soil Surface CO₂ Flux

• Main Authors: Xiaoling Wang, Shenglei Fu, Jianxiong Li, Xiaoming Zou, Weixin Zhang, Hanping Xia, Yongbiao Lin, Qian Tian, Lixia Zhou
• Format: Article
• Language: English
• Published: MDPI AG 2019-02-01
• Series: Forests
• Subjects: CO₂ production and diffusion; soil properties; CO₂ emission; surface soil layer
• Online Access: https://www.mdpi.com/1999-4907/10/2/192

In order to gain more detailed knowledge of the CO₂ concentration gradient in forest soil profiles and to better understand the factors that control CO₂ concentration along forest soil profiles, we examined the soil surface CO₂ flux, soil properties and soil profile CO₂ concentration in upright (CK), inverted and mixed soil columns with a depth of 60 cm in two subtropical forests in China from May 2008 to December 2009. The results showed that: (1) The SOC (soil organic carbon), TN (total N) and microbial biomass were higher in the deeper layers in the inverted soil column, which was consistent with an increase in CO₂ concentration in the deeper soil layer. Furthermore, the biogeochemical properties were homogenous among soil layers in the mixed soil column. (2) CO₂ concentration in the soil profile increased with depth in CK while soil column inversion significantly intensified this vertical stratification as the most active layer (surface soil) was now at the bottom. The stratification of CO₂ concentration along the soil profile in the mixed soil column was similar to that in CK but it was not intensified after soil was mixed. (3) The soil surface CO₂ flux did not significantly change after the soil column was inverted. The surface CO₂ flux rate of the mixed soil column was higher compared to that of the inverted soil column but was not significantly different from CK. Our results indicated that the profile soil CO₂ production was jointly controlled by soil properties related to CO₂ production (e.g., SOC content and soil microbial biomass) and those related to gas diffusion (e.g., soil bulk density and gas molecular weight), but the soil surface CO₂ flux was mainly determined by soil surface temperature and may be affected by the intensity of soil disturbance.