These results suggested that about half or more than half SOC stock accretions under fertilization were induced by increase in non- labile SOC fractions. The corresponding changes of the sum of very labile and labile SOC fractions were 8.6, 6.8, 6.6, 3.2 and -1.6 Mg ha-1 at QY, GZL, ZZ, CQ and JX, respectively. Also, NPKM increased total SOC stock by 18.3, 16.2, 14.4, 10.5, and 6.5 Mg ha-1 at QY, GZL, ZZ, CQ and JX, respectively. The corresponding changes of the sum of very labile and labile SOC fractions were 2.6, 2.0, 1.8, 0.8 and -0.5 Mg ha-1 at ZZ, QY, GZL, CQ and JX, respectively. Results showed that SOC stocks varied among sites (GZL, JX, CQ > ZZ, QY) and generally increased with fertilizations (CK-1 at ZZ, GZL, QY, CQ and JX, respectively.

Based on five two-decade Chinese long-term fertilization experiments (GZL: Gongzhuling ZZ: Zhengzhou CQ: Chongqing JX: Jinxian QY: Qiyang) under three fertilization treatments (CK: cropping with no fertilizer input NPK: chemical nitrogen, phosphorus and potassium fertilizers and NPKM: NPK with manure input), we quantified very labile, labile, non- labile and total SOC stocks at 0-20cm soil depth. Soil organic carbon (SOC) storages are altered under long-term fertilization in croplands, it however remains unclear how fast- to slow-cycling SOC fractions each respond to fertilization practices. Labile and Non- labile Soil Carbon Fractions Equally Contributed to Carbon Changes under Long-term Fertilization

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