| Under the background of global warming,understanding the responses of soil organic carbon decomposition to temperature change is of great significance for clarifying the relationship between soil carbon cycle and global climate change.With incubation test,this paper studied the effects of different temperatures(10,30 and 50℃)on the soil organic carbon mineralization and humus composition in six major crop soils(dark brown soil,albic soil,sandy soil,alluvial soil,meadow soil and black soil)at Jilin province.The results are as follows:1.CO2 releasing rate was fast during the earlier phase of incubation,and then slow during the later phase of incubation.CO2 accumulative releasing amount increased with the extension of incubation time.With increasing incubation temperatures,CO2 releasing rate and accumulative releasing amount increased gradually in several types of soil under the condition of not adding corn straw.In addition to alluvial soil and meadow soil,organic carbon mineralization rate of the rest of soils were in the order of 30℃>50℃>10℃during the earlier phase of incubation(0~13d),and were in the order of 50℃>30℃>10℃after 13 days under the condition of adding corn straw.CO2 accumulative releasing amount under the condition of adding corn straw was higher than the condition of not adding corn straw.With increasing incubation temperatures,soil organic carbon mineralization rate increased.Soil organic carbon mineralization rate under the condition of adding corn straw was higher than the condition of not adding corn straw.The above results indicated that temperature increasing was not conducive to sequestration of soil organic carbon.2.Under the condition of not adding corn straw,the temperature sensitivity coefficient(Q10)of sandy soil,alluvial soil,meadow soil and black soil in low temperature range(10~30℃)were lower than that of high temperature range(30~50℃),but dark brown soil and albic soil were opposite.Under the condition of adding corn straw,the value of Q10 in low temperature range(10~30℃)were higher than that of high temperature range(30~50℃)in several types of soil.3.With increasing incubation temperatures,soil and its humus components carbon(HEC,HAC,FAC and HUC)contents decreased generally.The contents of water soluble organic carbon(WSOC)was the highest at 50oC.The ratio of humic acid carbon and fulvic acid carbon(HAC/FAC)decreased generally with increasing incubation temperatures under the condition of not adding corn straw.Incubation temperatures had not identical effect for the HAC/FAC ratio under the condition of adding corn straw.Soil and its humus components carbon contents and the HAC/FAC ratio at the condition of 10℃and 30℃under the condition of adding corn straw were higher than the condition of not adding corn straw.These results indicated that the high temperature(50℃)was beneficial to the accumulation of WSOC,but was not conducive to the accumulation of soil and its humus components carbon.Adding corn straw could increase the contents of soil and its humus components organic carbon.4.With increasing incubation temperatures,the proportion of 2–0.25 mm aggregate,the mean weight diameters(MWDs)of water-stable aggregates and the soil organic carbon(SOC)contents in the different aggregate size fractions were tended to decreased.The above results indicated that the high temperature had a negative impact on soil aggregation and aggregate stability,and was not favorable for the accumulation of soil aggregate organic carbon.5.Across different moisture levels,soil and its humus components carbon(HAC,FAC and HUC)contents decreased and the ratio of humic acid carbon and fulvic acid carbon increased with increasing incubation temperatures.The contents of WSOC was the highest at 50oC.Across different incubation temperatures,the soil total organic carbon(TOC)contents decreased and the ratio of humic acid carbon and fulvic acid carbon increased with increasing moisture levels.The above results indicated that the increase in temperature and moisture was generally not favorable for the accumulation of TOC and was more favorable for the formation of HA.Temperature increase was not favorable for the accumulation of HAC,FAC and HUC.High temperature was favorable for the accumulation of WSOC.6.With increasing incubation temperatures,the ratios of alkyl C/O-alkyl C,aliphatic C/aromatic C,hydrophobic C/hydrophilic C,and O-alkylC/aromatic C in HA all tended to decreased.The ratios of aliphatic C/aromatic C and O-alkylC/aromatic C in HU also decreased,whereas the ratios of alkylC/O-alkyl C and hydrophobic C/hydrophilic C tended to increase with the increase in temperature.These results indicated that an increase in temperature induced the HA structure to be less alkylated,aliphatic,and hydrophobic and more decomposed,whereas the HU structure tended to be less aliphatic and more decomposed,alkylated,and hydrophobic.Across different moisture levels,aliphatic C/aromatic C and O-alkyl C/aromatic ratios in HA tended to decrease,whereas hydrophobic C/hydrophilic C ratio tended to increase with increasing incubation temperature.Aliphatic C/aromatic C and O-alkyl C/aromatic ratios in HU tended to decrease,whereas hydrophobic C/hydrophilic C ratio tended to increase with increasing incubation temperature.The above results indicated that across different moisture levels,an increase in temperature induced the HA and HU structure tended to be less aliphatic,more decomposed,and more hydrophobic. |
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