The Study On Formation And Transformation Of Soil Humus Under Special Incubation Condition

Soil humus is a special compound of a great amount of molecules in soil. It has important regulative function in soil fertility, structure and character. Its formation and transformation have relationship with environmental factors. In this paper, first, laboratory incubation experiment was used to study the changes of the dynamic amount and characters of soil microbial carbon (SMBC), soil organic carbon (SOC), humin (HM), humic acid (HA), fulvic acid (FA) and the changes of humus composition from chernozem added organic materials under the conditions of different oxygen (O₂) and carbon dioxide (CO₂) concentrations during organic materials decomposition. The responses of SOC and its compositions under the circumstances of different O₂ and CO₂ concentrations were discussed during organic materials decomposition. Second, the responses of SOC and its compositions on Free-air CO₂ enrichment were studied by Nanjing FACE experiment. All of studies not only had provided theoretical foundation for demonstrating the realationship between the mechanisms of formation, transformation of humus and driving factors of humus, but also probably had offered new information in order to reseach greehouse effects, which is of greatly scientific significance . Firstly, in soil system, CO₂ pressure increased because of CO₂ concentration enrichment in the atmosphere. Pressure difference between the atmosphere and the soil air made gas exchanging, therefore, CO₂ concentrations increased in the soil air. CO₂ concentration rised, meanwhile O₂ concentrations dropped because CO₂ and O₂ concentrations ebbed and flowed each other ,which restrained the activity of aerobe and made the ability that microorganism decomposes soil organic materials weakened, hence, SOC are accumulated. Secondly, FACE experiment was builded in the soil-plant system. On one hand, Growth of radicle was speeded with CO₂ concentration enrichment. During early days CO₂ concentrations enrichment promoted root biomass and the losing of root amounts was speeded during late days,which more root biomass transfered into the soil, so input more Carbon into the soil, on the other hand, CO₂ concentrations enrichment strengthened photosynthesis of plant and assimilation carbon rised in plant through photosynthesis. Rising assimilation carbon of defoliate also input more carbon into the soil. Rising carbon quantities enhanced the ratio of C/N, the activity of microorganism was restrained because of nitrogen shortage, therefore, SOC was accumulated.The major results were as follows:(1)Under simulating experiment indoors, the amounts of soil microbe and SMBC increased after adding certain amount of corn stalk ,and then the amount of SMBC decreased gradually with prolonging of incubation time .But different concentrations of gas incubation had different effects on SMBC. High O₂ and low CO₂ increased the amount of SMBC; the amount of SMBC was decreased under low O₂ and high CO₂.(2) SOC in all treatments increased after adding corn stalk ,and then the amount of SOC decreased gradually with prolonging of incubation time. Under different concentrations of gas incubation, high O₂ and low CO₂ accelerated decomposition, and made content of SOC decrease obviously ; low O₂ and high CO₂ did good to accumulation of SOC.(3) After adding some amount of corn stalk, WSOC of all treatments rosed, and then the amount of WSOC dropped with prolonging of incubation time. After the 180th day, the amount of WSOC tended to the steady state . Under different concentrations of gas incubation, high O2 and low CO2 were benifical to decomposition of WSOC ; low O2 and high CO2 were benificial to accumulation of WSOC.(4)The amounts of HE, HA, FA of all treatments increased previously and then decreased after adding of corn stalk, the turning time was respectively 7th day ,15th day ,7th day . Under different concentrations of gas incubation, high O2 and low CO2 were benificial to the formation and accumulation of HE, HA, whereas low O2 and high CO2 were benificial to the formation and accumulation of FA.(5)According to the former research on the relative amount of HA,FA and compositions of humus(PQ), after adding of corn stalk, the formation rate of FA was more than HA in the initial stages of decomposition , and HA was gradually more than FA with prolonging of incubation time, After the 180th day the composition of humus tended to the steady state. That is to say, the formation order of FA was earlier than HA.(6) During the corn stalk decomposition, under different concentrations of gas incubation low O2 and high CO2 were benificial to accumulation of HM.(7) AlogK of HA,FA increased in all treatments ,but RF decreased after adding corn stalk, which showed that the degree of soil humifiction fell down and the molecular of HA,FA became simplified. Under the conditions of different concentration of gas incubation high O2 and low CO2 were benificial to increase the degree of oxidation and aromaticity of HA and the molecular structure of FA became simplified. Low O2 and high CO2 were benificial to simplification of the molecular structure of HA and complexity of the molecular structure of FA.(8) After adding corn stalk, the degree of activation of HA,FA in all treatments were higher than CK, which showed that the proportion of aliphatic alkene was increased. Under different concentration of gas incubation, high O2 and low CO2 were benificial to complexity and aromaticity of the HA structure, and aliphaticity of the FA structure. Low O2 and high CO2 were benificial to aliphaticity of the HA structure.(9) Under the conditions of Free-air CO2 enrichment (FACE), the amounts of SOC ,FA incresed dramatically. The amounts of WSOC were much higher than CK in the 0-15 cm soil deepth. The amounts of SOC, WSOC, HA, FA, HM in the 0—15cm soil deepth were all more than in the 15—30cm deepth.(10) Under different O2 and CO2 incubation, SOC and WSOC was positive correlative notably, as well as SOC and SMBC, SOC and HE, SMBC and HE, HE and FA.During early days and metaphase of corn stalk decomposition, HA and FA was negative correlative notably. HA and FA ebbed and flowed each other. During anaphase of organic materials decomposition, HA and FA was positive correlative notably.