Effect of Vegetation Succession on Organic Carbon, Carbon of Humus Acids and Dissolved Organic Carbon in Soils of Copper Mine Tailings Sites

Carbonofhumusacids(HSAC)anddissolvedorganiccarbon(DOC)arethemostactiveformsofsoilorganiccarbon(SOC)andplayanimportantroleinglobalcarbonrecycling.WeinvestigatedtheconcentrationsofHSAC,water-solubleorganiccarbon(WSOC),hotwater-extractableorganiccarbon(HWOC)andSOCinsoilsunderdifferentvegetationtypesoffourcopperminetailingssiteswithdifferingvegetationsuccessiontimeperiodsinTongling,China.TheconcentrationsofHSAC,WSOC,HWOCandSOCincreasedwithvegetationsuccession.WSOCconcentrationincreasedwiththeaccumulationofSOCinthetailings,andalinearlypositivecorrelationexistedbetweentheconcentrationsofHSACandSOCinthetailings.However,thepercentagesofHSACandDOCintheSOCdecreasedduringvegetationsuccession.TherateofSOCaccumulationwashigherwhenthesuccessiontimewaslongerthan20years,whereasthespeedsofsoilorganicmatter(SOM)decompositionandhumificationwereslow,andtheconcentrationsofHSACandDOCincreasedslowlyinthetailings.Thepercentageofcarbonofhumicacid(HAC)inHSACincreasedwithvegetationsuccession,andthevaluesofhumificationindex(HI),HAC/carbonoffulvicacid,alsoincreasedwiththeaccumulationofHSACandSOCinsoilsofthetailingssites.However,theHIvalueintheeachofthetailingswaslessthan0.50.ThehumificationrateofSOMwaslowerthantheaccumulationrateofSOM,andthelevelofsoilfertilitywasstillverylowinthetailingsevenafter40yearsofnaturalrestoration.