| Soil organic carbon (SOC) comprise around 1500 Pg C, twice that in the atmosphere, so the soil carbon pool plays an important role in global carbon balance, especially the soil organic carbon pool. Soil organic matter mineralization is a fundamental process, it’s a key process in the geochemical cycle, it’s important for us to grasp the mechanism of this process if we want to manage and utilize this giant carbon pool.In 1976, the paradox of SOC mineralization which is that even if 90% of the soil microorganisms are destroyed by CHC13 fumigation, following fumigant removal, SOC mineralization continues at the same rate as in the undamaged soil, challenges the generally recognized viewpoint that the mineralization rate of soil organic matter are controlled by soil microbial activity, therewith, a new theory called the ’Regulatory Gate Hypothesis’ was proposed to explain this phenomenon, it considered that mineralization of SOC is a two stage process:non-bioavailable humified SOC is altered by abiological processs to bioavailable forms (K1), the now bioavailable SOC is mineralized by the soil microbial biomass (K2).To provide evidence for the ’Regulatory Gate’ hypothesis in controlling soil organic matter mineralization, we tested the abiotic release of SOC from soil, the changes in soil microbial populations due to CHCl3, and the effect of soil environment factors (moisture, temperature, granular structure) on the rate of SOC mineralization. The main results are as follows:(1) We found a statistically significantly linear correlation (R2=0.97) between biomass C and ATP in aerobic soils, different type of soils had a similiar microbial ATP concentration, giving a mean biomass ATP concentration of 7.90 ± 2.24 μmol·g-1 biomass C. However, there was no discernable relationship between biomass C and ATP in soils incubated anaerobically, the comparable ATP concentrations in the naturally waterlogged paddy soils and the waterlogged upland soils strongly suggest no adaptation, the mean biomass ATP concentration was very much lower, at 2.83 ± 0.82 μmol ATP·g-1 biomass C, it may reflect differences in community structure between soils, soil redox potentials and/or differences in the volumes of air trapped in the pores of the soils.(2) To killed most of the microorganisms by 4 cycles of fumigation-incubation, slowly pumping CHCl3 saturated water to stop the activity of surviving microorganisms, meanwhile, collect and analyse any abiologically produced substrate carbon, after 60 days’ continuous perfusion, we found that six different type of soils would continuously released soluble organic carbon; After freeze drying, to add the extracts of four soils back to soil by the addition amount of 0.04%(W/W), the extra amount of CO2 during the incubation made up 53.02%,49.41%,39.97% and 44.04%, respectively. Even though we couldn’t make quantitative analysis and eliminate the interference of priming effect, while the result showed that there should be a part of the CO2 was from the mineralization of extracts. To inoculate the same amount of fresh soil into fumigated soils, and to treat the soils with multiple fumigation-incubations, there was no significant difference between different microbial population gradient. The ATP results of different fumigation-incubation cycles showed that only the first fumigation could destroy more than 85% of microbial population, the sbsequent fumigations can only kill less than 30% of the microorganisms.To combine the inoculation and multiole fumigation-incubation, it indicated that the rate of SOC mineralization is independent of microbial population.(3) Air-dry and rewet, freeze-thaw and sieving had different perturbations on moisture, temperature and particle structure, and had ifferent influence on microbial biomass, idirectly. Air-dry decreased 55.8 ± 1.4% of the microbial biomass, fumigation destroyed more than 80% of the microorganisms, the microbial population of -80℃ and -20℃ freezing declined -25.2 ± 2.2% and 15.6 ± 1.8%, respectively, while sieving had no effect on microbial biomass population. However, the rate of CO2 evolution still kept at the original level, and through high-throughput sequencing result, we found that the community structure of different treatments especially air dry-rewet and fumigation had significant differences.These results indicated that the rate of SOC mineralization was not controlled by microbial activity, and independent of microbial population and community structure, provided strong evidence for the ’Regulatory Gate Hypothesis’.
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