The Apparent Soil Respiration Flux And Organic Carbon Mineralization Simulation In Typical Wetlands In Yellow River Delta

In this paper, apparent soil respiration fluxes were measured for24hours insuccession day and night using Li-8100Type Open-circuit Soil CO2Flux System forfour times. Measurements were carried out in September2012, January, April andJuly2013respectively in Phragmites wetland and bare land in typical wetlands inthe Yellow River Delta. The diurnal and seasonal variations of soil CO2fluxes andthe related influential factors were analyzed. The process of soil organic carbon(SOC) mineralization was simulated in the laboratory to study the organic carboncontent, water content, and salinity on soil mineralization. The results showed that:In January, Soil CO2Flux had no obvious diurnal variation, and the values were0.02±0.01and0.01±0.01μmol m-2s-1in Phragmites wetland and bare land,respectively. In April, July and September, CO2Flux in Phragmites wetland were0.14±0.44,0.42±0.08,0.39±0.16μmol m-2s-1，and0.05±0.02,0.22±0.13,0.01±0.02μmol m-2s-1in bare land, respectively. CO2Flux had significant difference in thesethree months (p<0.05). But they had the same daily variation characteristic, whichwas in a U-shaped curve. The maximum was observed at about12:00am, theminimum occurred at about6:00am. Soil CO2Flux in reed field was significanthigher than that in bare land at the same month (p<0.05). CO2Flux in the YellowRiver delta reed wetland was significantly lower than that in the Yangtze estuary(chongming dongtan).A signifcant exponential relationship was found between soil CO2Flux andtemperature (T), the regression equations wereF=0.042e0.085TP(R2adj=0.881，p<0.001) andF0.113NP=0.004eT(R2adj=0.799，p<0.001) respectively in Phragmites wetland andbare land, this means that T is the primary environment reason constrained soilrespiration flux. In addition, soil CO2Flux had significant negative correlationrelationship with soluble salt (R2adj=-0.745，p<0.01) and electricity conductivity(R2adj=-0.738，p<0.01), and a weak positive correlation with SOC.SOC mineralization simulation experiments which lasted for70days inlaboratory had showed that the mineralization rate dropped rapidly in the first10days, then, it decreased slowly (11-35day) until late in the steady state (36-70day).Cumulative mineralization amount of SOC increased exponentially with time. As theexperiment lasted for a long time, restricted carbon in soil began to decompose.None of the three kinds of classical dynamics model can describe organic carbonmineralization process effectively when SOC was0.8g kg-1. But when SOC washigher than9.5g kg-1, the double exponential model has good fitting (R2adj＞0.99)for restricted carbon was mineralizaed in an exponential form in later period ofculture.Multi-factor variance analysis showed that SOC content was the main reasonfor the difference of the mineralization (F0.05=3711, p<0.001), there was a significantpositive correlation relationship between them (R2adj=0.775, p<0.05). Among it, theactive carbon, DOC and light component of organic carbon (LFOC) content was themain reason for the differences of the cumulative mineralization (R2adj=0.660~0.894,p<0.01). For soil moisture, its effects on SOC mineralization was second only toorganic carbon content (F0.05=71.31, p<0.001), SOC mineralization rate increasedwith the increase of moisture when it was below125%WHC. The rate was restrainedin flooded condition (250%WHC), but still higher than in drought condition(45%WHC). For the reason that salt content was much higher in the cultivated soil,higher than the level of soil secondary salinization, therefore, salinity had lessadverse effect on SOC mineralization (F0.05=33.58, p<0.001), but still had significantnegative linear correlation between them (R2adj>0.85, p<0.01). Multiple regression analysis showed that the relationship among SOC mineralization, SOC, moisture andsalinity satisfied the following equation:F=0.0039W2+1.41W9.06S+26.56C(Radj2=0.964, n=48).