Distribution And Sequestration Of Straw Carbon And Nitrogen In Soil Aggregates Under Plastic Film Mulching And Fertilization

The decomposition and sequestration of straw carbon（C）and nitrogen（N）in soil are affected by plastic film mulching（abbreviation as mulching）and fertilization treatments.However,the distribution and sequestration characteristics of straw C and N in soil aggregates under different mulching（including with/without mulching）and fertilization（including no fertilizer application,CK;single application of nitrogen fertilizer,N₄;organic fertilizer application combined with nitrogen fertilizer,M₂N₂）treatments were still not very clear.In this study,¹³C¹⁵N double-labeled technique was used to analyze the relative contribution of straw-derived C and N to total organic C and N of soil aggregates,quantify the distribution percentages of straw C and N in organic C and N fractions（particulate organic carbon,POC;particulate organic nitrogen,PON;mineral associated organic carbon,MOC;mineral associated organic nitrogen,MON）within soil aggregates,to clarify the main sequestration forms of straw C and N in soil aggregates,and further to explore the effects of mulching and fertilization on the distribution and sequestration of straw C and N within soil aggregates.This study would provide a basis for improving soil organic matter in the Black Soil area of Northeast China.The main research results were showed as follows:（1）Under no mulching,N₄treatment increased the content of straw-derived organic C(¹³C_agg)of>0.25 mm aggregate by 36.36%and 20.69%compared with M₂N₂ and CK treatments,respectively.Under mulching,the N₄ treatment increased the content of ¹³C_agg of each size aggregate by 22.87%～53.37%compared with the other treatments（M₂N₂ and CK）.Under no mulching,N₄ treatment decreased the content of straw-derived N(¹⁵N_agg)of<0.053mm aggregate by 31.01%compared with the CK treatment.Under the same fertilization treatment,the contribution percentages of straw C and N to total organic C and N of<0.053mm aggregates under the mulching were 34.81%and 17.50%less than those under no mulching,respectively.The average percentages of straw C and N distributed in>0.25 mm aggregate were22.22%and 42.14%,respectively.（2）The percentage of straw-derived POC(¹³C-POC)in ¹³C_agg was 64.70%and 47.59%,and that of straw-derived PON(¹⁵N-PON)in ¹⁵N_agg within>0.25 mm and 0.25-0.053 mm aggregates was 51.19%and 36.21%,respectively.N₄ treatment increased the content of ¹³C-POC within>0.25 mm aggregates,on average,by 55.39%compared with the other treatments（CK and M₂N₂）regardless of mulching or not.Regardless of mulching or not,the average percentages of straw C and N distributed in POC and PON within>0.25 mm aggregate were18.89%and 27.44%,and were increased by 51.98%and 48.30%in N₄ treatment compared with the other treatments,respcetively.（3）Under no mulching,the N₄ treatment reduced the contents of straw-derived MOC(¹³C-MOC)and straw-derived MON(¹⁵N-MON)within>0.25 mm aggregates,on average,by 24.18%and 40.49%compared with the other treatments（CK and M₂N₂）,respectively.Under mulching,the N₄ and M₂N₂treatments,on average,decreased the contents of ¹³C-MOC and ¹⁵N-MON within>0.25 mm aggregates by 19.74%and 23.13%relative to CK treatment,respectively.（4）The contribution percentage of straw C to MOC and that of straw N to MON within different sizes（>0.25 mm and 0.25～0.053 mm）aggregates were less than 13.00%.The average percentages of straw C distributed in MOC within>0.25 mm and 0.25-0.053 mm aggregates were 7.64%and 3.74%in all treatments,respectively.The average percentages of straw N distributed in MON within>0.25 mm and 0.25-0.053 mm aggregates were 20.19%and 9.22%in all treatments,respectively.In conclusion,straw carbon and nitrogen were mainly sequestrated in>0.25 mm aggregate and mainly existed as particulate organic carbon fraction after straw addition to soil.Single application of nitrogen fertilizer promoted the sequestration of straw carbon and nitrogen as particulate organic matter in>0.25 mm soil aggregates.No mulching promoted the renewal of carbon source in mineral associated organic matter within 0.25-0.053 mm aggregates,while mulching facilitated the renewal of carbon and nitrogen sources in mineral associated organic matter within>0.25 mm aggregates.