| Understanding soil organic carbon (SOC) dynamics, sequestration mechanism and itsinfluencing factors is meaningful for further exploring the potentials and ways of carbonsequestration. In order to reveal spatial-temporal distribution of SOC and the maininfluencing factors under different influencing factors (terrace age, soil type, altitude, slopeaspect, etc) after slope cropland changed into terraces in the hilly loess plateau of easternGansu Province, the terraces with different ages were chosen based on the way of interactionof time and space. By analyzing changes of the soil aggregates composition and theaggregates organic carbon contents, SOC sequestration mechanism in terrace was discussed.The main conclusions were as follows:1. The results demonstrated that the SOC content in0–60cm soil layer of the loessialsoil in terraces is continuously accumulated in a way of being slow down after quick in nearly50years after the terraces building. A carbon sink of0.78Tg was obtained after cultivatedloessial slope soil changed into terrace.（1）The content of SOC was increased significantly and exceeded the SOC content ofslope cropland with the increase of terrace ages during the initial8years（P＜0.01）.Significant increase of SOC was found after24years but there was no significant change later.Compared with the SOC content of slope cropland, the increasing ranges of SOC in20–40cmand40–60cm soil layers in50years later were increased by54.6%and52.4%, while theincreasing rage of0–20cm soil was only33.7%(P＜0.05), and the average accumulation rateof SOC was respectively247.9kg/(hm2a),66.7kg/(hm2a) and52.1kg/(hm2a).Compared with the SOC content of the slope land, the SOC stock of0-60cm soil layer ofcultivated loessial soil increased by0.78Tg after48years in Zhuanglang country, with anincreasing rage of38.5%.(2)The contents and accumulation rates of SOC were different indifferent soil types and terrains with the terrace age. The content of SOC in0–60cm layer ofthe dark loessial soil was maximum, followed by the red clay soil and cultivated loessial soil. The SOC accumulation in0–20cm layer of the loessial soil was the most obvious comparedwith the lower layers, whereas, there were significant increases of SOC in20–40cm and40–60cm layers in the red clay soil (P＜0.05). The SOC content in0–20cm layer in thenorthward slopes was higher than that in the southward slopes. Compared with the southwardslopes, the average of SOC in the northward slopes was increased by22.1%after25years.The SOC expressed an increasing trend with the increase of altitude.2. The bulk density increased after slope cropland changed into terraces, and thendecreased gradually and keep stable with the increase of terrace ages.(1)The bulk density of20-40cm soil layer was more than40-60cm soil layer, and thebulk density was the minimum. The bulk density of each soil layer was less than the level ofslopeland after restoration for16years.(2)The bulk density of the red clay soil was more thanthe dark loessial soil, and the bulk density of the cultivated loessial soil was the minimum.(3)The bulk density of0-20cm soil layer of the cultivated loessial soil in the sorthward slopeswas firstly decreased and later increased with the increase of altitude. The bulk density in thenorthward slopes was increased with the increase of altitude.3. The spatial-temporal variance of SOC was mainly influenced by soil types whichcould explain62.0%of the organic carbon variance. The slope aspect and altitude couldexplain20.4%of the variance in all, and the terracing age and organic fertilizer could explain11.7%and5.8%of the variance respectively.4. The content of>5mm soil aggregates accounted for the most majority of soilaggregates, aggregates and soil organic carbon have poor correlation,>5mm water-stableaggregates and SOC exist significant correlation.(1) The content of>5mm water-stable aggregates showed a trend that first increasedand kept stable with the increase of terrace ages.5-2mm,2-1mm,1-0.5mm and0.5-0.25mm water-stable aggregates expressed a trend that first decreases and then kept stable withthe increase of terrace ages. The content of>5mm water-stable aggregates was more thanother size water-stable aggregates. Destruction rate of soil aggregates changed in5.39%~29.15%, the aggregate destruction rate of new terrace soil destruction would be the maximum.(2)The content of>5mm water-stable aggregates in the sorthward slopes increased with theincrease of altitude, while the content of5-2mm,2-1mm,1-0.5mm and0.5-0.25mmwater-stable aggregates expressed a decreasing trend. The content of>5mm water-stableaggregates in the northward show a maximum of64.33%at1800-1900m.(3)There was asignificant positive correlation between>5mm water-stable aggregates and SOC, while5-2mm,2-1mm,1-0.5mm and0.5-0.25mm water-stable aggregates exhibit negativecorrelation. 5. It showed a significant correlation between large particle size aggregates organiccarbon and soil organic SOC, SOC mainly depended on the content of>5mm sizewater-stable aggregate. The changing characteristics of different particle size aggregatesorganic carbon in the same soil layer showed similar trends with the increase of terrace ages.(1)The average content of the same particle size aggregates organic carbon in thedifferent soil layers trended to be decreasing with the decrease of particle size level.(2)Theaggregates organic carbon in different particle size decreased with increase of soil layer depthunder different soil types. The aggregates organic carbon in0–60cm soil layer of the darkloessial soil was more than the red clay soil, and the cultivated loessial soil trends to be theminimum.(3)The aggregates organic carbon in the sorthward slopes increases with increaseof altitude, and5-2mm particle size aggregates organic carbon show a significant change.The organic carbon contents of aggregates in the northward slopes had a maximum at1800-1900m.(4) There was a positive correlation between aggregates organic carbon invarious particle size and SOC. The content of aggregates organic carbon of>5mm particlesize and SOC showed most significant positive correlation. |
PDF Full Text Request