The Response Of Soil Respiration In The Qinghai Lake Headwater Wetland To Warming And Thawing

The Qinghai-Tibet Plateau is a sensitive region of global climate change,which has a profound impact on soil freeze-thaw and soil carbon emission in this region.The response mechanism of soil respiration in alpine wetland to freeze-thaw alternation in non-growing season is still unclear.Therefore,this study took the wetland at the source of Qinghai Lake River（marsh meadow）as the research object,and carried out the OTC（Open-Top-Chamber）warming experiment for 2 years.Soil respiration rate,surface soil water heat and other indicators were monitored.The changes of freeze-thaw transition stage,the interaction characteristics of soil water and heat,and the changes of soil respiration during warming and freeze-thaw transition stage were analyzed.The results show that:（1）The alternation of freezing and thawing is mostly concentrated in the soil surface 5cm.Short-term warming increased the duration of freeze-thaw action in 5cm,10cm and 15cm soil during the early freezing period of autumn and winter.After long-term warming,the freeze-thawing time of soil surface 5cm increased,but the freeze-thawing duration of soil 10cm in autumn and winter early freezing period and winter and spring melting period decreased by 4d respectively.By increasing the volume water content（liquid water and frozen water）of soil surface 5cm,the freeze-thawing days of surface 5cm in winter and spring melting period,autumn and winter early freezing period and freezing period were increased.During the whole observation period,the soil temperature（Tw）of 5cm,10cm and15cm in the warming state was about 0.8°C,0.9°C and 0.86°C higher than that of the natural state.In the freeze-thaw transformation stage,the temperature increase in the non-freezing period is the highest.The surface volume water content increased by7.76%（P>0.05）,the 15cm volume water content increased by 9.21%（P<0.05）,and the10cm volume water content decreased by 2.33%（P<0.01）.There was a significant synergistic effect between soil moisture and soil temperature in winter and spring melting period,autumn and winter early freezing period and freezing period,and temperature and moisture were positively correlated.In the non-freezing period,the root biomass of 0-10cm in the soil surface accounted for43%of the root biomass of 30cm in the soil surface,so that the soil 0-10cm formed a temperature and water variation zone,and the root layer of 0-10cm played a good role in maintaining the hydrothermal stability of the soil below 10cm.（2）During the whole observation period,the mean soil respiration rate（Rsw）was1.298μmol·m^-2·s^-1 under warmer state and 1.055μmol·m^-2·s^-1 under natural state,which was 23.03%higher than that under natural state（P<0.05）.In winter and spring melting period,freezing period,non-freezing period,autumn and winter early freezing period,the increase of 69.78%,47.37%,20.56%and 4.11%compared with the natural state,respectively.During the observation period,soil respiration was regulated by soil temperature of 10cm in the warming state and 5cm in the natural state.In terms of the transformation of freeze-thaw pattern,the winter and spring melt period and the autumn and winter early freeze period under increasing temperature were mainly regulated by soil moisture at 10cm,and the freezing period and non-freezing period were mainly regulated by soil temperature at 10cm.In the natural state,the winter and spring melting period,the non-freezing period and the autumn and winter early freezing period are mainly controlled by the soil temperature of 5cm,and the freezing period is controlled by the soil volume water content of 5cm.The diurnal dynamic characteristics of soil respiration were affected by freeze-thaw in autumn and winter early freezing period,freezing period and winter and spring melting period.The"stimulating effect"of freeze-thaw on soil respiration was more significant than that of the natural state.The soil carbon emission model changed from the exponential model of non-freezing period with temperature rise to the"pulse"emission model of freezing period.（3）The average annual cumulative CO2 emissions were 1824.52 g CO₂·m^-2 and1484.03 g CO₂·m^-2 under warming and natural conditions,respectively.Increasing temperature increased the proportion of cumulative carbon emissions in non-growing season（melting period in winter and spring,early freezing period in autumn and winter,freezing period）,and decreased the proportion of cumulative carbon emissions in growing season（non-freezing period）.（4）During the observation period,temperature increase decreased the Q₁₀ value of soil respiratory temperature sensitivity coefficient of 5cm and 10cm,but increased the Q₁₀ value of soil respiratory temperature sensitivity coefficient of 15cm.The sensitivity coefficient Q₁₀ of soil respiration temperature was higher in non-growing season than in growing season when the temperature increased and in natural state.Increasing temperature decreased the soil respiratory temperature sensitivity coefficient Q₁₀ value in winter and spring melting period and freezing period,but increased the soil respiratory temperature sensitivity coefficient Q₁₀ value in non-freezing period.（5）The average values of Rs in the hot thaw sinkhole zone and the natural state during the observation period were 3.59μmol·m^-2·s^-1 and 4.52μmol·m^-2·s^-1,respectively,and the natural state was 25.9%higher than that of the hot thaw sinkhole zone（P<0.05）.The Q₁₀value of soil respiration in the hot melt sinkhole was 2.47,while that in the natural state was 2.16.The hot melt sinkhole is a sensitive area susceptible to climate change disturbances for many years.The OTC zone has higher temperature and volumetric water content than the natural state,and releases heat continuously to the surrounding area,which triggers the accelerated thawing of the surrounding permafrost zone.