A Basic Study on the Microbial Mechanism of Soil Organic Carbon Accumulation Structures under Different Fertilization Treatments of Long-Term Argo-Ecosystem Experiments
|School||Nanjing Agricultural College|
|Keywords||Long-term fertilization Soil respiration Carbon sequestration Soil microbial|
Biological stabilization within accumulated soil organic carbon (SOC) has not been well understood, while its role in physical and chemical protection as well as of chemical recalcitrance had been addressed in Chinese rice paddies. In this study, topsoil samples were collected and respiratory activity measured in situ following rice harvest under different fertilization treatments of three long-term experimental sites across southern China in 2009. The SOC contents, microbial biomass carbon (SMBC) and nitrogen (SMBN) were analysed using chemical digestion and microbial community structure assessment via clony dilute plate counting methods.The main results were as follows:1. SOC and TN contents were consistently higher under compound chemical fertilization (Comp-Fert) or combined organic and inorganic fertilization (Comb-Fert) compared to N fertilization only (N-Fert) and no-fertilizationg. Compared to chemical fertilization, SOC under Comb-Fert was higher 7.3% and TN under Comb-Fert was higher 7.4%.2. There was significant different of micro biomass carbon(SMBC) and micro biomass nitrogen (SMBN) under different fertilization treatments. SMBC and SMBN contents were consistently higher under Comb-Fert compared to Comp-Fert and no-fertilization treatments. When subtracting the background effect under no fertilization treatment (Non-Fert), the increase both in SMBC and SMBN under fertilization treatment was found very significantly correlated to the increase in SOC over controls across the sites.3. According to results of clony dilute plate counting methods, the culturable bacteria population number, was ranging from 0.84×107CFU·g-1-6.90×107 CFU·g-1, and the culturable fungi population was ranging from 4.66×104 CFU·g-1-27.84×104 CFU·g-1. no significant differences was found in culturable bacteria population number under different fertilization treatments in all sites. Culturable fungi population number was higher under combined chemical and straw fertilization treatment of WJ site and combined chemical and manure fertilization treatment of JX site There was significantly higher fungal-bacterial ratio (F/B ratio) under Comb-Fert than under N-Fert and Comp-Fert. And the F/B ratio was well correlated with soil organic carbon contents in all samples across the sites studied.4. Soil respiration was ranging from 6.90 gCO2·m-1·d-1-16.84 gCO2·m-2·d-1. Mineralization intensity was ranging from 0.09gCO2-C·gSOC-1·m-2·d-1-0.27gCO2-C·gSOC-1·m-2·d-1. Metabolic quotient was ranging from 1.99 mgCO2-C-mgSMBC-1·m-2·d-1-14.27 mgCO2- C·mgSMBC-1·m-2·d-1. No significant regulary was found in the three indices above under fertilization treatments. Fertilization treatments made differences in diversity of fungi, which was higher in combined straw and chemical fertilization than other treatments. But no significant differences was found under fertilization in diversity of bacteria.5. While the ratio of culturable fungal to bacterial population numbers (F/B ratio) was well correlated with soil organic carbon contents in all samples across the sites studied, the increase both in SMBC and SMBN under fertilization treatment was also found very significantly correlated to the increase in SOC over controls across the sites. But the specific soil respiratory activity based on microbial biomass carbon was found in a significantly negatively correlation with the SOC contents for overall samples. That means SOC accumulation favoured a build-up the microbial community with increasing fungal dominance in the rice paddies under fertilization treatments.