Variation characteristics of organic carbon fractions within macroaggregates under different fertilization regimes in the reclaimed soil

To better understand the mechanism of soil organic carbon (SOC) sequestration and provide a scientific basis for improving soil fertility and quality in the reclaimed coal mining subsiding region,it was investigated the response of variation characteristics of organic carbon (OC) fractions within macroaggregate to fertilization regimes in the reclaimed soil.Topsoil samples (0-20 cm) were collected from the different treatments of a 6 year reclaimed field.The variation characteristics of OC fractions within macroaggregates (coarse particulate organic carbon referred to as cPOC,fine particulate organic carbon referred to as fPOC,intra microaggregate particulate organic carbon referred to as iPOC and mineral associated organic carbon referred to as MOC) and relationships between them and SOC concentration were analyzed using physical fractionation method.Four different fertilization treatments were no fertilizer (CK),chemical fertilizer with nitrogen,phosphorus and potassium (NPK),organic manure alone (M) and chemical fertilizer combined with manure (MNPK).Compared with CK,the application of chemical fertilizers (NPK) had no effect on the OC contents in any macroaggregate fractions.However,the application of manure alone (M) significantly decreased MOC content by 36.45%.Application of manure combined with chemical fertilizers (MNPK) markedly increased cPOC and fPOC contents,which were 4 and 2 times higher than CK,but it greatly decreased MOC content by 39.01%.Among the four fractions,only cPOC and fPOC contents were significantly positively correlated with SOC concentration,indicating that SOC was primarily sequestered in the unprotected OC fractions within macroaggregates in the reclaimed soil.The SOC sequestration rates in the treatments of CK,NPK,M and MNPK are 0.82,0.68,1.36 and 1.58 mg/(ha·a).SOC sequestration rate was significantly positively correlated with annual carbon input (R2=0。58,P