Evaluating soil carbon stability by combining δ13C and soil aggregates after afforestation on agricultural land and thinning management

Abstract

Background and AimsAfforestation 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 13 C. MethodsSoil 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. ResultsWe found that afforestation on agricultural land signi cantly 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 signi cantly 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 δ 13 C, controlled by soil aggregates, signi cantly decreased in each soil aggregate after afforestation while increased after thinning. Additionally, the carbon concentrations, C/N and δ 13 C of small-size particles (< 0.25 mm) and the distribution of SMAC are important for soil carbon indicators (SOC, C/N, CO 2 uxes and δ 13 C). ConclusionWe conclude that soil aggregate distribution shows a recovery tendency for soil carbon, suggesting that increasing thinning intensity is bene cial for the accumulation of older carbon and the e ciency of nitrogen in more stable fractions.