川西高寒山地土壤有机碳与铁、铝矿物复合体分布特征

Distribution of soil organic carbon associated with Al and Fe minerals within alpine mountain soils in western Sichuan

为了量化川西高寒山地土壤与铁、铝矿物相关的有机碳含量以及探讨川西高寒山地土壤铁、铝矿物对有机碳稳定性和累积方式的影响,采用选择性提取法研究了川西高寒山地的山地灰化土(MP)和高山草甸土(AM)中土壤有机碳与晶质金属氧化物(DH)提取、短程有序(HH)提取、矿物复合体以及有机—金属配合物(PP)提取中的有机碳和铁、铝的分布。结果表明,MP中DH,HH和PP提取的碳含量分别为(10.91±6.23)g/kg、(5.92±1.66)g/kg和(8.76±2.29)g/kg,分别占有机碳的20.92%,12.07%和19.93%;而AM中DH、HH和PP提取的碳含量分别为(9.05±1.33)g/kg、(5.52±1.02)g/kg和(9.12±3.21)g/kg,分别占有机碳的21.04%、12.47%和19.34%。3种提取剂提取的碳含量以及其占有机碳的百分比在MP和AW的A层土壤中均表现为PP>DH>HH,而在B层土壤中则表现为DH>PP≈HH。随着土壤深度的增加,深层土壤中次级矿物和晶体矿物丰度的显著增加,导致有机碳与铁、铝矿物复合体由有机—金属配合物主导转变为有机碳与晶质金属氧化物形成的复合体主导。PP提取的碳和其所占有机碳的百分比表现为A层高于B层,而DH和HH提取的碳含量和其所占有机碳的百分比大体表现为A层低于B层。由于MP特殊的土壤性质,这种差异在MP中更为明显。3种提取剂提取的金属(Al+Fe)含量在两种土壤中均表现为DH>HH>PP。而其提取的碳与金属的摩尔比表现为DH<HH<PP,说明随着铁、铝矿物的结晶度增加,其与有机质的作用从共沉淀、络合而向吸附作用转变。DH,HH和PP提取的碳与SOC的相关分析表明,MP中土壤有机碳的累积在一定程度上受晶质铁、铝矿物与有机质的相互作用而驱动;AM中土壤有机碳的累积在一定程度上受短程有序矿物与有机质的相互作用以及有机—金属配合物的驱动。本文研究表明,土壤中的铁、铝矿物与有机碳形成的复合体在一定程度上驱动着川西高寒山地土壤有机碳的积累,不同土壤类型中,与矿物相关的有机碳的分布不同,其有机碳的积累方式也不同。

The chemical protection mechanism of soil organic carbon(SOC)was explored to quantify the distribution of organic carbon protected by iron(Fe)and aluminum(Al)minerals in two alpine soils.Selective extraction methods were used in mountain podzolic(MP)soil and alpine meadow(AM)soil to investigate the distribution of SOC,as well as Fe and Al contents of SOC associated with crystalline metal oxides extracted by(dithionite-HCl,DH),short-range-order minerals extracted by(hydroxylamine-HCl,HH)and organo-mineral complexes extracted by(Na-pyrophosphate,PP).Results showed that the carbon concentrations extracted by DH,HH,and PP in MP soils were(10.91±6.23)g/kg,(5.92±1.66)g/kg,and(8.76±2.29)g/kg,respectively.These oxides,minerals,and complexes accounted for 20.92%,12.07%,and 19.93%of SOC,respectively.Comparatively,the carbon concentrations for DH,HH,and PP in AM soils were(9.05±1.33)g/kg,(5.52±1.02)g/kg,and(9.12±3.21)g/kg,accounting for 21.04%,12.47%,and 19.34%of SOC,respectively.The distribution of carbon contents and their proportions to SOC extracted through three extractants showed an order of PP>DH>HH in the A horizon and an order of DH>PP≈HH in the B horizon,for both MP and AM soils.An increase in soil depth,together with increasing abundance of secondary minerals and crystalline minerals in deeper soils,leads to organo-mineral associations changing from being dominated by organo-metal complexes to being dominated by the crystalline mineral-associated organic carbon.PP-extracted carbon contents and its relative proportion to SOC were higher in the A horizon than those in the B horizon,whereas DH-and HH-extracted carbon contents and their proportions to SOC were generally lower in the A horizon than those in the B horizon.These differences were more pronounced in MP because of its special soil property.The distribution of metal(Al+Fe)contents extracted by the three extractants showed the order DH>HH>PP in both soil types.However,the molar ratio of carbon-to-metal showed the order DH<HH<PP,suggesting that as the degree of mineral crystallization increases,the interaction between minerals and carbon changed from precipitation dominant to adsorption dominant.A correlation analysis of DH,HH,PP,and SOC suggested that the accumulation of SOC was driven to a certain extent by the association of crystalline Fe and Al minerals and organic matter in MP,as well as the association of short-range-order minerals and organic matter as well as organo-metal complexes in AM soils.The organomineral associations are,to some extent,driving the accumulation of SOC in alpine mountain soils in western Sichuan.The distribution of organic carbon associated with minerals and the accumulation ways of organic carbon is different across various soil types.