不同林龄柳杉人工林土壤有机碳和根际效应的变化特征

[Objective]Complex root-soil interactions may cause variations in rhizosphere soil organic carbon(SOC)dynamics with stand development that differ from those in bulk soil.However,how stand age affects particulate organic C(POC)and mineral-associated organic C(MAOC)in the rhizosphere and bulk soil,as well as the rhizosphere effects on SOC pools,remains to be elucidated.[Method]Here,we investigated the contents of total SOC and its components(POC vs MAOC)in the rhizosphere and bulk soils and further assessed the patterns of the rhizosphere effects on SOC pools along a chronosequence(6,15,25,35,and 55 years)of Cryptomeria japonica var.sinensis plantations.[Result](1)The total SOC and POC contents in both compartments initially increased and then stabilized during stand development,despite a decrease in MAOC content in the 55-year-old stand,as the soil environment of the over-mature plantation slightly inhibited microbial growth and activity.(2)The POC/SOC decreased and MAOC/SOC ratios increased in bulk soil from 9-year-old to 35-year-old plantation,while contrasting trends were common in rhizosphere soil.(3)The total SOC content was 83.0%significantly higher in the rhizosphere compared to bulk soil while the rhizosphere effect on total SOC decreased with stand age,indicating substantial but diminishing rhizosphere capacity for organic C formation and accumulation during stand development.Moreover,the rhizosphere effects on POC and MAOC,mediated by root traits(related to chemistry and morphology),were directly related to soil and microbial properties,respectively,with the rhizosphere effect on total SOC primarily determined by the effect on MAOC.[Conclusion]Collectively,our findings indicate that over-mature plantations still promote SOC sequestration,and underscore that simultaneous tracking of the rhizosphere effects on POC and MAOC helps elucidate the mechanisms of root-induced organic C sequestration during plantation development.