全新世年代框架约束下的东北地区土壤有机碳储库时空格局

SPATIOTEMPORAL VARIATION OF WELL-DATED SOIL ORGANIC CARBON POOL IN NORTHEAST CHINA DURING THE HOLOCENE

土壤有机碳储库是全球碳循环的重要单元,明确土壤有机碳储库的时空分布及其与气候的关系是有效发挥土壤碳封存作用的前提。本研究以东北地区半湿润-半干旱气候梯度带22个全新世实测土壤剖面为对象,在AMSC、 OSL年代约束下,以千年窗口碳密度为框架建立区域全新世土壤有机碳密度的时空分布模式,从剖面序列和区域尺度分析全新世气候变化对土壤有机碳密度时空分布的影响。结果显示,东北地区土壤有机碳密度自全新世以来明显增加,12~9 ka、 9~6 ka、 6~3 ka和3~0 ka时段累积的土壤有机碳密度分别为2.21 kg/m^(2)、 4.28 kg/m^(2)、 6.92 kg/m^(2)和9.83 kg/m^(2);在空间上,全新世土壤有机碳密度整体上自西南向东北呈增加趋势,东北部高值区为35~50 kg/m^(2),西部低值区为4~9 kg/m^(2)。无论在空间分布还是时间分布上,东北地区全新世土壤有机碳密度均受气候要素(尤其湿度)控制。这表明,全新世生物生产力较为稳定,当气候偏冷湿时有利于土壤有机碳的积累,这也意味着未来气候变暖不利于区域土壤有机碳的积累封存。

Soil organic carbon pool plays a critical role in regulating atmospheric COconcentration,as soils offer promise for carbon sequestration. However,the adding of chronology to dynamic changes in soil organic carbon pool on a regional or global scale is scarce. It is clear that more research is needed to obtain spatio-temporal variation of soil organic carbon storage. For Northeast China,it is one of the continuous distribution areas covered by mollisol in the world,and plays an important role in the global carbon cycle. Thus it can offer the effective sections to investigate temporal and spatial variation of soil organic carbon storage and its relation with regional climate.Here,we compiled 22 Holocene soil sections along the semi-humid and semi-arid climatic gradient in Northeast China( 38° 40’ ~ 53° 30’N,115° 05’ ~ 135° 02’E),including 18 new sampled sections( MTGX,TQX,QQHEE1,QQHEC2, BAB3, DQB1, NJC4, NHA1, BAC2, SHE1, BQE2, HEBA1, QQHED1, JMSA2,JMSB1,SYA5,SYB1 and SYC2) and 4 published sections( XLHT,TPS,BLZ,NRTA). These sections are mainly constituted of mollisol,loess-paleosol and sandy paleosol,which developed during the Holocene. They are used to reconstruct the temporal and spatial distribution of soil organic carbon density( SOCD) during the Holocene based on works of14C and OSL dating,together with measurement of total organic carbon content( TOC),soil bulk density( BD) and soil thickness( h). In detail,408 TOC data from 16 sections from the age of the Holocene and248 TOC data from 22 sections from the depth intervals of 1. 0 ~ 0 m were used to estimate the SOCD. The SOCD of a 1000-year bin width( SOCD1 ka) was calculated as: SOCD1 ka= TOC1 ka×BD1 ka×h1 ka×10,where TOC1 ka,BD1 kaand h1 kaare respectively the average values of TOC,BD and h for the interval. In addition,the spatial and temporal distribution of SOCD during the Holocene were generated using ArcGIS 10. 5 and the inverse distance weight( IDW) method. Further,both the magnetic susceptibility and the color index of MTGX section are measured for tracing the Holocene climate change in the study region,with regional lake records. Ultimately,we explore how and to what extent climate affects the temporal and spatial patterns of the Holocene SOCD in the region.The results showed that the SOCD in Northeast China increased significantly during the Holocene,and the cumulative carbon density was 2. 21 kg/m^(2) ,4. 28 kg/m^(2) ,6. 92 kg/m^(2) and 9. 83 kg/m^(2) respectively during the interval of 12 ~ 9 ka,9 ~ 6 ka,6 ~ 3 ka and 3 ~ 0 ka. From 10 ka to 3 ka,the cumulative rate is more remarkable. In case of the spatial variation,the Holocene SOCD exhibited an increased trend from southwest to northeast,with a high value of 35 ~ 50 kg/m^(2) in the northeast region and with a low value of 4 ~ 9 kg/m^(2) in the west region. Similarly,the SOCD of the depth intervals of 1. 0 ~ 0 m also exhibited an increased trend from southwest( 3 ~ 5 kg/m^(2) ) to northeast( 15 ~ 23 kg/m^(2) ). The spatial variation of SOCD of the depth intervals of 1. 0~0 m is similar to that of the interval of 9 ~ 0 ka,with an inverse pattern of the interval of 12 ~ 9 ka in the study region. For temporal and spatial variation of SOCD in Northeast China,the carbon density is closely related to climate during the Holocene,especially it is roughly proportional to increases in precipitation( spatial domain: R^(2) = 0. 22;temporal domain: R^(2) =0. 44) and cold-wet index( spatial domain: R^(2) = 0. 26;temporal domain: R^(2) = 0. 66). Inversely there is a negative correlation between the Holocene SOCD and both temperature( spatial domain: R^(2) = 0. 24;temporal domain: R^(2) =0. 001) and dryness index( spatial domain: R^(2) = 0. 22) in the region. Moreover,the relationship between cold-wet index and the Holocene carbon density was stronger than that of other climate variables. A significant inference from the results is that a colder and wetter climate may have favored organic carbon accumulation during the Holocene,when gross primary productivity was stable. We speculate that the ongoing global warming would result a loss of soil organic carbon. In addition,the Holocene SOCD accumulated by the 1000-year bin width is higher than that of the depth intervals of 1. 0 ~ 0 m in Northeast China. It implies that the approach to estimate the SOCD with a reliable chronological framework can act as a significant reference for the future investigation of soil organic carbon storage.