Legacy effect of elevated CO_(2) and N fertilization on mineralization and retention of rice (Oryza sativa L.) rhizodeposit-C in paddy soil aggregates

Rhizodeposits in rice paddy soil are important in global C sequestration and cycling.This study explored the effects of elevated CO_(2) and N fertilization during the rice growing season on the subsequent mineralization and retention of rhizodeposit-C in soil aggregates after harvest.Rice(Oryza sativa L.)was labeled with ^(13)CO_(2) under ambient(400 ppm)and elevated(800 ppm)CO_(2) concentrations with and without N fertilization.After harvest,soil with labeled rhizodeposits was collected,separated into three aggregate size fractions,and flood-incubated for 100 d.The initial rhizodeposit-^(13)C content of N-fertilized microaggregates was less than 65%of that of non-fertilized microaggregates.During the incubation of microaggregates separated from N-fertilized soils,3%–9%and 9%–16%more proportion of rhizodeposit-^(13)C was mineralized to ^(13)CO_(2),and incorporated into the microbial biomass,respectively,while less was allocated to soil organic carbon than in the non-fertilized soils.Elevated CO_(2) increased the rhizodeposit-^(13)C content of all aggregate fractions by 10%–80%,while it reduced cumulative ^(13)CO_(2) emission and the bioavailable C pool size of rhizodeposit-C,especially in N-fertilized soil,except for the silt-clay fraction.It also resulted in up to 23%less rhizodeposit-C incorporated into the microbial biomass of the three soil aggregates,and up to 23%more incorporated into soil organic carbon.These results were relatively weak in the silt-clay fraction.Elevated CO_(2) and N fertilizer applied in rice growing season had a legacy effect on subsequent mineralization and retention of rhizodeposits in paddy soils after harvest,the extent of which varied among the soil aggregates.