Exploring the role of the rhizosphere in soil carbon cycling: impacts on pools and components of SOC along a chronosequence of Cryptomeria japonica plantations in subtropical China

Abstract

Background

The rhizosphere plays a critical role in forest soil organic carbon (SOC) dynamics. However, the patterns and drivers of SOC and its components within rhizosphere and bulk soils, as well as rhizosphere effects, remain unclear throughout stand development.

Methods

We examined SOC, particulate organic carbon (POC), and mineral-associated organic carbon (MAOC) contents in both rhizosphere and bulk soils, alongside fine root traits and associated soil and microbial parameters, across a 9- to 55-year chronosequence of Cryptomeria japonica plantations in subtropical China.

Results

SOC, POC, and MAOC contents increased from young (9-year-old) to mature (35-year-old) plantations in both rhizosphere and bulk soils. In over-mature stands (55 years old), MAOC content in rhizosphere and bulk soils decreased compared to maturity, while SOC and POC contents remained consistent. SOC and POC contents in the rhizosphere were 83.0% and 232.2% greater than those in bulk soil, respectively. The rhizosphere effect on SOC decreased with stand age, primarily driven by its impact on MAOC. This was associated with decreased rhizosphere effects on soil nutrient availability, microbial properties, and root traits. The rhizosphere effect on soil nutrient availability accounted for a larger proportion of the variance in the rhizosphere effect on SOC than root traits and microbial properties.

Conclusion

Extending plantation age can promote SOC sequestration but may compromise SOC stability. This study provides direct evidence of the crucial role that rhizosphere processes play in soil carbon dynamics and contributes valuable insights to the sustainable management of plantations and the mitigation of global climate change.