| Long-term fertilization leads to the differences in water,heat,nutrients and microbial activities between topsoil and deep soil,which changes the decomposition and turnover of straw carbon（C）in soils.Soil aggregates are the sites for organic C retention.However,the distribution and sequestration of straw C in topsoil and deep soil aggregates were not very clear.Based on a long-term experimental station in Shenyang Agricultural University,the topsoil（0～20 cm）and deep soil（40～60 cm）samples from different fertilization treatments（organic manure combined with chemical nitrogen fertilizer,M2N2;chemical nitrogen fertilizer,N4;no fertilizer,CK）were mixed with 13C-labeled straw for in-situ incubation.We analyzed the content of organic C and itsδ13C value among soil aggregates（>0.25 mm,0.25～0.053 mm and<0.053 mm）and organic C fractions（particulate organic C,POC;mineral associated organic C,MOC）within soil aggregates（>0.25 mm and 0.25～0.053 mm）,qualified the relative contribution of straw-derived organic C to total organic C of the aggregates in topsoil（0～20 cm）and deep soil（40～60 cm）,compared the difference in the distribution of straw C in organic C fractions within aggregates between topsoil and deep soil,and investigated the effect of fertilization on the sequestration characteristics of straw C in aggregates of topsoil and deep soil.This research would provide references for soil C sequestration and soil sustainable development.The main results were showed as follows:（1）Compared with fertilization treatments（N4 and M2N2）,CK treatment increased the content of straw-derived organic C of<0.053 mm aggregate in the topsoil by 106.67%and that of>0.25 mm aggregate in the deep soil by 34.25%.The contribution percentage of straw-derived C to total organic C of>0.053 mm aggregate in the deep soil was about two times of that in the topsoil.About 22.57%and 11.39%of straw C was distributed to the>0.25 mm and<0.25 mm aggregates of topsoil,respectively.And about 29.35%and 8.74%of straw C was distributed to the>0.25 mm and<0.25 mm aggregates of deep soil,respectively.（2）Compared with CK treatment,fertilization treatments（N4 and M2N2）increased the contents of straw-derived MOC and straw-derived POC witnin 0.25～0.053 mm aggregate of deep soil,on average,by 81.25%and 71.43%,respectively.The contents of straw-derived MOC and straw-derived POC within>0.25 mm aggregate of the deep soil were,on average,63.64%and 21.94%larger than that within>0.25 mm aggregate of the topsoil,respectively.（3）The average percentage of straw C distributed to POC within>0.25 mm aggtegate was 15.83%and 19.21%,and that distributed to MOC within>0.25 mm aggtegate was 6.20%and 10.14%in the topsoil and deep soil,respectively.Regardlass topsoil or deep soil,the percentage of straw C distributed in MOC and POC within 0.25～0.053 mm aggregate was less than 5.00%.The average percentages of straw C distributed in POC within>0.25 mm aggtegate of topsoil and deep soil were 21.31%and 51.46%larger in the CK treatment than those in the fertilization treatments,respectively.The average percentages of straw-derived POC contributed to total POC within>0.25 mm and 0.25～0.053 mm aggregate of deep soil were 82.14%and 52.39%,and were increased by 216.65%and 70.26%compared with the topsoil,respectively.In conclusion,straw carbon remains as particulate organic carbon fractions in soil macroaggregates,and straw addition promotes the regeneration and sequestration of carbon in deep soil macroaggregates.In deep soil,feilization improves the incorporation of straw carbon into organic carbon fractions of 0.25～0.053 mm aggregate,which would play an impartant role in stabilization and sequestration of deep soil organi carbon. |
