Soil organic carbon mineralization of coastal soils with different salinity levels.

In order to accurately evaluate the SOC(soil organic carbon) mineralization characteristics of different salinized soils in the Yellow River delta, and their controlling factors, six salinized soils with different salinization levels(BZ1 and BZ2 were bare land soils, BZ3~BZ6 were farmland soils) were collected from sample sites at different distances from the sea, and the SOC(soil organic carbon) mineralization rate was determined by laboratory thermostatic incubation. The results showed that the salinization levels of the six soils tended to increase in line with the proximity of their respective sample sites to the sea. During the 255-day incubation period, the relationships between mineralization rates of SOC and duration of incubation in all the treatments fitted the logarithmic function equation(P<0.01), and the SOC mineralization rates of the bare land soils were much lower than those of the farmland soils(P<0.05). The dynamic variation of the cumulative SOC mineralization with incubation time fitted the first-order kinetics equation(P<0.01). The simulation results showed that SOC mineralization potentials differed significantly between the different salinized soils, and that SOC mineralization potentials of bare land soils were much lower than those of farmland soils(P<0.05). The correlation analysis showed that SOC mineralization was significantly positively correlated with SOC content, total nitrogen(TN) content, and microbial biomass(correlation coefficient:0.975, 0.954, and 0.893, respectively), and was significantly negatively correlated with soil total salt content(correlation coefficient:-0.813). There were significant negative correlations between soil total salt content and SOC, and TN and microbial biomass(correlation coefficients:-0.838, -0.876, and -0.843, respectively), while there was no significant correlation between soil total salt content and ratio of bacteria to fungi(correlation coefficient:0.784). Soil salinity may control SOC mineralization by affecting microbial biomass, or by affecting soil C and N sequestration. However, we did not find any significant influence of microbial community structure on SOC mineralization in this study.