| As a "sink" landscape on the land area, riparian buffer strip of reservoir also releases pollutants to water. On one hand, as the reduction of ecological function, a healthy riparian buffer zone can’t totally retain and transform the incoming nitrogen and phosphorus pollutants, but may brings some non-point pollutants into the water at the same time. On the other hand, plant litter plays an important role in maintaining soil function and improving soil fertility through decomposition of plant residues, but increases the risk of releasing nutrients into the water simultaneously. Studying potential of C and N mineralization has great significance for understanding carbon and nitrogen cycling of the ecosystem and predicting potential threat to water of belt along the shore-land of reservoir. Rich vegetation types including herbs and other plants grow in Danjiangkou reservoir shore. The net C and N mineralization was studied in a laboratory incubation experiment at25℃for61days. Typical yellow brown soil was collected, and four kinds of associated vegetation was sampled from Danjiangkou reservoir shore. The vegetation were grouped to citrus and cnidium group and fleabane and abutilon group. The objective of this paper was to evaluate, under the laboratory conditions, the effects of riparian plant initial residue composition on net C and N mineralization in riparian soil, and further to understand C and N dynamics in soils following the application of plant residues from riparian buffer strip in Danjiangkou Reservoir.(1) Vegetation has priming effect on soil carbon mineralization. Cumulative carbon mineralization amount of soil amended with plant residues was significant higher than the CK during the entire incubation period. During the61days of incubation, the soil amended vegetation released1478.53mg·kg-1to2448.36mg·kg-1CO2-C, and the CK released646.47mg·kg-1CO2-C. The citrus leaf (GL) had the highest cumulative C mineralization amount and the cnidium monnieri cauline root (SR) had the lowest one. The released CO2-C accounted for9.53%～14.54%of organic carbon in the cultivation matrix, which was0.54-1.36times higher than the control group. The cumulative C mineralization amount of soil amended with stem leaf was higher than that of root in the same plant. Organic carbon mineralization rate was the fastest in the first3days, the daily cumulative mineralization amount was76.5mg·kg-1to220.2mg·kg-1, which was significantly higher than the medium and later stage. The mineralization accumulation amount in the first3days accounted for15%～30%of the total amount for all plants. The dynamics of carbon mineralization preferably followed the first order kinetics equation.(2) The NO3--N content is7.58～20.34times of the NH4+-N content, so soil nitrogen mineralization was mainly composed of NO3--N. The N mineralization of stem leaf is significantly higher than that of root. By the end of incubation, Net N mineralization amount of citrus leaf (GL) and abutilon stem leaf (QL) is higher than other treatment, the order was GL (99.52mg·kg-1)> CK (79.53mg·kg-1)> QL (71.62mg·kg-1). The mineralization rate soared from the3rd day to the51th day, and then it kept stable. The mineralization amount of citrus leaf with fleabane stem leaf(GL+PL) and citrus leaf with citrus fleabane root(GL+PR) were negative in the previous stage (3-21d), then gradually increased after the21th day, their net N mineralization amount were46.34mg·kg-1and46.21mg·kg-1on the61th day. The soil organic nitrogen content of cnidium monnieri stem leaf with abutilon stem leaf (SL+QL) and Cnidium monnieri root with abutilon stem leaf (SR+QL) in the first41days were negative, mainly microbial immobilized and increased in the later stage. The nitrogen mineralization amount of root and mixed root samples varied from-7.82mg·kg-1to-6.86mg·kg-1throughout the incubation period. At the end of the incubation period, nitrogen mineralization amount of GL was99.52mg·kg-1, exceeded9.99mg·kg-1than that of the control group, while the others were less than the control group, indicated that adding citrus leaf (GL) promoted the soil nitrogen mineralization, whereas other plants had the inhibiting effect on soil N mineralization. The final N mineralization amount of citrus root (GR), fleabane root (PR), citrus root with fleabane stem leaf (GR+PL) and citrus root with fleabane(GR+PR) was negative.(3) The vegetation quality had a strong influence on carbon and nitrogen mineralization, the mineralization rate was positively correlated with nitrogen concentration of plant residues, whereas it was negatively correlated with lignin, C/N and L/N.(4) Composite vegetation was not significantly different with those of individual vegetation in carbon or nitrogen mineralization. There was no significant addition reaction between the two mixed vegetation. Consequently, individual plant can be used to estimate the dynamic change of carbon and nitrogen mineralization. |
PDF Full Text Request