| The low temperature condition in cold zones makes the soil accumulate organic carbon easily, and thus the density of soil organic carbon is relatively high; on the other hand, the warming extent in the regions with low temperature is obviously greater than that in warm regions. So, the change of soil carbon pool and the sensitivity of soil respiration were studied in several typical regions with low temperature in China. Using the National Multi-purpose Regional Geochemical Survey data, soil carbon reserves were estimated; the temporal and spatial variation of soil carbon pool were investigated combining with the historical data, and natural and artificial reasons for the change were analyzed. Soil respiration experiment were done in the laboratory, and the characteristics of soil respiration and its the temperature sensitivity in low-temperature regions were explored, so as to better understand the respond of soil organic carbon pool in low-temperature regions to the temperature change under global warming. In addition, different components of soil organic carbon were divided by three experimental methods. The main results are as follows:First, surface soil in the north area of the Songnen Plain was the carbon source from the whole aspect, with an average carbon-release ratio of 1479 t/km2, and the potential amount of soil carbon emission was 0.20 Gt in 20 years, which was equivalent to that of fossil fuel combustion 0.21 Gt; resulting from climate warming, land use and soil erosion, the values of soil organic carbon emission were 0.11 Gt, 0.09 Gt and 0.19 Mt, respectively. Under the existing mode of farming and land use, the potential of carbon sequestration in the Songnen Plain is negative.Second, the central and western area of Jilin was also the carbon source, and with a annual change rate of 0.199 tC ha-1·a-1, organic carbon was released from the soil into the atmosphere. Among the affecting factors, LUCC brought soil carbon sequestration; the change of carbon pool in the central and western area of Jilin was not obviously affected by temperature change, but it had a significant correlation with precipitation variation, which can largely explain that the SOC density is Northwest low, southeast high in spatial distribution, and gradually increases from northwest to southeast in trend.Third, soil respiration of different land use types showed significant positive feedback to temperature increase, which increases exponentially or in power-type as the temperature increase, while temperature sensitivity coefficient Q10 decreases with increasing temperature. The experiment of black soil in the Northeast area showed that at the same temperature, of different land use types, soil respiration in forest was highest, that in paddy field was higher than that in dry farmland, and that in grassland was between that in paddy field and that in dry farmland.Fourth, the feedback of permafrost samples in the Qinghai-Tibet Plateau and in the region of Mohe was sensitive to temperature increase; soil respiration increased exponentially or in power-type with the temperature, and temperature sensitivity coefficient was higher at low temperature. Using the model fitting methods of two pools and three pools, dynamic variation of soil carbon pool were fitted, and the result was that the contents of active carbon were 0.117~0.342 g/kg and 0.158~0.795 g/kg, respectively, and the proportion of active carbon to total amount of carbon pool were 0.17%~2.89% and 0.52%~8.75%, respectively.Fifth, by density separation, acid hydrolysis and chloroform fumigation, soil organic carbon was divided in the physical, chemical and microbiological sense, respectively. As to the same soil samples, the proportion of easily oxidized carbon measured by acid hydrolysis to soil dry weight was the highest, followed by that of light fraction carbon from density separation, and that of microbial biomass C measured by chloroform fumigation was the lowest.
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