Thermal Sensitivity Of Forest Soil Organic Carbon Mineralization Under Constant Vs.varying Tempeautre Regimes And Their Mechanisms In Changbai Mountain

Take two kinds forest soil in changbai mountain（"coniferous forest " and " broad-leaved forest "）,and each of two soil layers（layer "A" and "O"）,for the soil sample.Respectively incubation under the “constant temperature high”（“constant high”,30 ℃）、“constant temperature low”（“constantlow”,10 ℃）and 10 30 ℃ circulating temperature conditions（“Variable high”and “Variable low”）for 4 months.Determination the soil respiration rate（RS）in different periods,and thus calculate the Q₁₀ by the constant and varying temperature pattern.In order to explore mechanism of temperature sensitivity characteristic differences,also in the different periods of soil water soluble organic carbon（WSOC）and the content of lignin and polyphenols.The research shows that RS under different processing consistent Performance for “VLow” < "CLow","VHigh" > "CHigh"（p < 0.001）,and the Q₁₀ of constant temperature（average 2.23）was significantly higher than the Q₁₀ of varying temperature（average 1.51）（p < 0.001）.Different forest types and soil layers RS was also sensitive to temperature changes,its present that “coniferous forest” > “broad-leaved forest” and layer "A" > layer "O".These differences may be related to constant and variable temperature cultivation mode of soil microbial community structure and variation on the substrate availability.Therefore,when measuring the soil respiration Q₁₀ should consider the effects of temperature changes.In terms of WSOC,total WSOC content in the soil under different temperature model overall decline are smaller and the difference was not significant（p > 0.05）.But in the cold water soluble organic carbon（CWSOC）or hot water soluble organic carbon（HWSOC）,constant between low and high constant or variable temperature at the beginning of the incubation（the first month）there were significant differences（p < 0.001）.In terms of CWSOC,its characterized was “CLow” > “Chigh ”≈ varying temperature.But HWSOC’s characterized is “CLow” < “Chigh” ≈varying temperature.Its shows that the soil water soluble organic carbon under different temperature patterns of consumption as well as the differences between soil microbial activity.In addition,WSOC content of different kind of forest between the difference temperature changes was sensitive to not significant（p > 0.05）,but there are still significant differences between the soil layer : layer “O” > layer “A”（p < 0.001）.In lignin,the lignin content in the soil under different temperature pattern also showed a sharp decline on the whole,and difference reached significant level（p < 0.001）.Specific conditions for “CLow” < “Chigh” ≈ varying temperature.In addition,in lignin oxidation degree of each index in the reaction,all show rise firstly and fall later,this may be associated with similar-lignin formation.And as one of the main degradation products of lignin,the temperature has less effect on the results of polyphenol’s content,than the difference of forest type or soil layers.But the influence has reached significant level（p < 0.001）.And also presents “CLow” < “Chigh” ≈ varying temperature.And the highest polyphenol content was in the first month——its also the period of maximum degree of oxidation of lignin,this is Conform to the theory of the polyphenols in soil mainly comes from the decomposition of lignin.As a whole,soil carbon mineralization of temperature sensitivity is different for the forest soils of changbai mountain under the constant temperature and varying temperature: the latter is higher than the former,and this regular exists in different forest types and soil layer.In the process,the easy mineralization in soil carbon pool——represented by WSOC,and hard mineralized carbon pool——represented by lignin were all be consumed.but the former in different temperature mode has a lager different by the sequence and the degree of consumption,while the latter is not obvious in this respect.The main reason of difference between two kinds of carbon mineralization temperature sensitivity characteristics should be derived from the thermal adaptability of microorganism and the change of soil quality of it caused.