| Soil organic carbon (SOC) is an essential part of soil organic matter. It plays a significant role in the maintenance of soil fertility and agroecosystem. Plant residue is the important source of SOC and affects the accumulation of SOC during its decomposition. While it is not clear about how plant residue carbon (C) from different parts of maize was distributed and sequestrated in soil and how soil different in fertility affected the turnover of residue C. Stable isotope tracing technique was employed to distinguish between plant residue C (exogenous new C) and soil native C (old C).13C labeled root, shoot and leaf were separately added into soil different in fertility and incubated in lab with constant temperature and moisture. This study analyzed the contents of residue carbon C in SOC, microbial biomass C (MBC) and soil aggregates. Results showed as follows:(1) The addition of root, shoot and leaf increased the content of SOC. And SOC content decreased gradually with incubation time. SOC content was higher in soil added with leaf than in soil added with root and shoot before 180 days. After 180 days, SOC content was higher in soil added with shoot than in soil added with root and leaf. At the end of incubation, significant different in SOC was found among in low fertility soil added with different residue (P＜0.05). The average of SOC content was 11.95 g kg-1,11.32 g kg-1 and 11.51 g kg-1 in low fertility soil added with shoot, root and leaf, respectively. In high fertility soil, the average of SOC content was 16.54 g kg-1,16.19 g kg-1 and 16.20 g kg-1 in soil added with shoot, root and leaf, respectively, but there was no significant among in different residue additions (P>0.05).(2) Exogenous new C content followed the same trend as SOC content in the two kinds of fertility soil. Exogenous new C was higher in soil added with leaf than in soil added with root and shoot before 1 day. At the end of incubation, exogenous new C was equal in the three treatments of the same soil fertility. The average of exogenous new C was 1.38 g kg-1 in low fertility soil and was 1.62 g kg-1 in high fertility soil. At the end of incubation, the residue rate was 33.01% in low fertility soil added with root, and that was lower than in low fertility soil added with shoot and leaf. However, the residues rate was 38.34% in high fertility soil added leaf, and that was lower than in high fertility soil added with root and shoot.(3) Microbial biomass C (MBC) decreased gradually with incubation time. MBC was lower in low fertility soil than in high fertility soil. The average of MBC was 45.33 mg kg-1 in low fertility soil added with root, shoot and leaf and there was no significant difference among in different residue additions (P>0.05). MBC was 45.12 mg kg-1 in high fertility soil added with leaf and was 69.43 mg kg-1 in that added with root and shoot. MBC derived from residue C increased gradually with incubation time during 1-7 days and 30-60 days, but it decreased gradually during other incubation periods in low fertility soil. MBC decreased gradually with incubation time in high fertility soil. Dissolved organic C (DOC) decreased gradually with incubation time. Dissolved organic C (DOC) derived from residue C accounted for 4%-10% of total DOC.(4) The addition of root, shoot and leaf increased the organic C content in soil aggregates. Firstly, exogenous new C enriched in 2-0.25 mm aggregates. The content of exogenous new carbon increased gradually in>2 mm aggregates with incubation time, and it increased by 30%-50% at the end of incubation. The exogenous new C decreased gradually with incubation time in 2-0.25 mm aggregates, and it decreased by 50%-65% at the end of incubation. The exogenous new C increased after the first reduction in the 0.25-0.053mm aggregates, while it decreased gradually with incubation time in<0.053 mm aggregates. The content of exogenous new C was higher in>0.25 mm aggregates of soil added with shoot than that added with root and leaf.All the results indicated that the distribution and sequestration of exogenous new carbon in soil and soil aggregates was controlled by its source and soil fertility level. It needs to further explore the microbial dynamics caused by different sources of residue C and soil fertility levels in soil aggregates. |
