| Summary: | Understanding the relationships between carbon; nitrogen, their stable isotopes δ<sup>13</sup>C and δ<sup>15</sup>N, and soil stoichiometry may further our understanding of the regulatory mechanisms of the soil quality index on the equilibrium on isotopic fractionation. Four plantations of <i>Zanthoxylum planispinum</i> var. <i>dintanensis</i> (5–7, 10–12, 20–22 and 30–32 years) in the karst plateau gorge area, Guizhou Province, China, were selected to determine the variation characteristics and interactions between leaves, leaf litter, soil carbon (C), soil nitrogen (N) and their isotopes with plantation age, and to explore the relationship between soil stoichiometry and the isotopes δ<sup>13</sup>C and δ<sup>15</sup>N. The results were as follows: (1) the δ<sup>13</sup>C in leaves, litter, and soil were −28.04‰ ± 0.59‰, −26.85‰ ± 0.67‰, and −19.39‰ ± 1.37‰, respectively. The contents of δ<sup>15</sup>N were 2.01‰ ± 0.99‰, 2.91‰ ± 1.32‰, and 3.29‰ ± 0.69‰, respectively. The contents of δ<sup>13</sup>C and δ<sup>15</sup>N were ranked in the order, soil > litter > leaf. (2) With increasing plantation age, the soil <sup>13</sup>C decreased; the leaf and the litter δ<sup>15</sup>N increased first then decreased, and the litter δ<sup>13</sup>C and the soil δ<sup>15</sup>N did not vary significantly. (3) The litter layer was positively correlated with soil δ<sup>13</sup>C and negatively correlated to δ<sup>15</sup>N. (4) Redundancy analysis showed that the soil microbial biomass carbon (MBC) and the bacteria/fungi (BAC/FUN) were the dominant factors affecting the natural abundance of C and N isotopes
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