Evaluate soil C stability by combining δ13C and soil aggregates after afforestation and thinning on larch plantations

Abstract

Background and Aims Afforestation and thinning management are effective ways to mitigate global warming. The mechanism of soil carbon recovery is effectively explored by linking soil aggregate and isotopic 13C. Methods Soil samples were collected from nearby agricultural land (AL) and larch plantations (established in 1965 and thinning in1995, UT: 2500 tree ha− 1, MT: 1867 tree ha− 1, and ST: 1283 tree ha− 1). The soil was separated into three aggregates (LMAC: >2 mm, SMAC: 2-0.25 mm, MIC: 0.25 − 0.053), minerals associated with organic matter (MAOM: <0.053 mm), and carbon fractions within macroaggregate. Results We found that afforestation on agricultural land significantly increased mean weight diameter (MWD). But thinning intensifying decreased MWD resulting from the distribution of LMAC replaced by SMAC. Moreover, after afforestation, the carbon concentration in soil aggregates and MAOM was significantly decreased, and the C stability of macroaggregates was weakened, while could be strong after thinning. Thinning decreased the C/N in soil aggregates and MAOM and the effect of thinning intensity on C/N was obvious with the shrinking of particle size. The δ13C, controlled by soil aggregates, significantly decreased in each soil aggregate after afforestation while increased after thinning. Additionally, the carbon concentrations, C/N and δ13C of small-size particles (< 0.25 mm) and the distribution of SMAC are important for soil carbon indicators (SOC, C/N, CO2 fluxes and δ13C). Conclusion We conclude that soil aggregate distribution shows a recovery tendency for soil carbon, suggesting that increasing thinning intensity is beneficial for the accumulation of older carbon and the efficiency of nitrogen in more stable fractions.