Changes Of Soc In Agricultural Soils And The Temperature Dependence On C Minrealization And CO₂ Evolution In Paddy Soils

The soil carbon pool is the biggest one in the earth surface system and the soil organic carbon (SOC) plays an important role in global carbon cycling. The global warming induced from the greenhouse effect and its impact on the terrestrial ecosystems is the focus on the international circles of geology, ecology, and environmental sciences, which is the key project in the frame of the Global Carbon Project, PAGES, IHDP and GCTE et al. Soils contain about 1500Pg (lPg=lGt=10¹5g) of organic carbon worldwide, which is about three times the amount of carbon in vegetation and twice the amount in the atmosphere. Soil carbon mineralization and the CO2 evolution has been paid attention due to its important effects on the global carbon cycle and terrestrial ecosystems.This paper deals with the effect of different crop rotation systems on the aggregates and their SOC accumulation in Paludalfs in North Huai Region; the effect of the cultivated leaf-harvesting Ginkgo on the SOC dynamics; and especially researches the effect of soil wanning on the SOC mineralization of the various paddy soil. The main results showed as follows:1. Organic Carbon Mineralization and CO2 Evolution of Paddy Topsoil and the Temperature Dependencea. The mean C mineralization rate of these paddy soils studied and the temperature dependence was relatively small compared to those of natural forest soils and grassland soils. This may support our previous finding of the SOC enhancement in paddy soils of China.b. C mineralization and O₁0 of paddy soils varied with soil type and soil N status. The labile C plays an important role in the mineralization of SOC in paddy soils while N bioavailability, to a lesser degree, also influence the C mineralization and the temperature dependence.c. Furthermore, our data here indicated that there was different sub-pool ofmineralizable C in the paddy soils which had different accessibility to mineralization and the response to wanning. When addressing the C mineralization and the CO2 evolution of paddy soil, labile C should be paid much attention and further study needed for modeling the response of paddy soils to global warming in the context of C mineralization and the temperature dependence.2. Response of the SOC of paddy soils with various fertilizer treatments on warming and daily variation of CO2 evolution in the fielda. The SOC of Huangnitu paddy soil in Tai Lake region is not sensitive to soil warming.b. Daily amount of soil respiration in spring and autumn are ranged from 271.78 to 409.17 mgC-CO2.m^-2.d^-1 and 197.26 to 336.72 mgC-CO₂.m^-2.d^-1. These data are much smaller than those in other lituratures.c. The daily amount of flux under the treatment of only applied inorganic fertilizer increase by 71% than of organic-inorganic fertilizer at most, which indicated long-term only application of chemical fertilizer may lead to significant increase of CO2 emissions and not be favor of carbon sequestration.3. Dynamics of SOC under the various crop rotation and land utilizationa. There is a signicfice in the particle size distribution, SOC contents and the natural abundance of ¹3C in these aggregates of Paludalfs under different crop rotation systems in North Huai region. Young carbon derived from corn tended to be accumulated in the coarse fractions as revealed by heavier stable carbon composition in those from deep layer under the rotation system containing corn crop.b. Land utilizatioin may affect the dynamics of SOC seriously.The effect of the cultivated leaf-harvesting Ginkgo on the SOC dynamics were studied. The results showed that when the agricultural soil (wheat) changed to the economic forests (Ginkgo), the content of SOC decreased yearly. Soil carbon should be paid attention in the research of global change as well as reclaiming soil fertility and food quality.