Effects Of Precipition Patterns On Soil Respiration In A Subtropical-warm Temperate Typical Coniferous And Broadleaved Mixed Forest

Since the Industrial Revolution,human activities have led to rising concentrations of greenhouse gases and global temperatures.Global warming leads to changes in global precipitation patterns through the global hydrological cycle.The changes in temperature and precipitation patterns have far-reaching impacts on terrestrial ecosystems and human socio-economic development.Forest ecosystem is an important part of terrestrial ecosystem carbon cycle,and its changes under global climate and precipitation changes also reflect global climate.The subtropical-warm temperate climate transition zone is the climate transition zone between north and south of China.The typical mixed coniferous and broadleaved forest in subtropical and warm temperate zones is also an important part of forest ecosystem in China,which is sensitive to climate change due to its special geographical location.Soil respiration dynamics are critical to understanding the ecosystem carbon cycle and its feedback to climate change.However,the mechanism about response to soil respiration under precipitation changes timing is still not clear.Therefore,it is extremely urgent to explore the response of soil carbon emissions to precipitation timing and precipitation intensity changes under precipitation pattern changes,and relevant results and mechanisms will help to understand and predict the carbon cycle pattern of terrestrial ecosystems under precipitation pattern changes in the future.We carry out precipitation control experiments（decrease precipitation 30%,natural precipitation and increase precipitation 30%）in the early winter and early spring in the coniferous and broad-leaved mixed forest in the Qinling-Huaihe regional subtropical-warm temperate climate transition.The following two questions were explored:（1）.The response of soil carbon emission to precipitation timing change in coniferous and broadleaved mixed forest,（2）.The key influencing factors of soil carbon emissions changes under different precipitation timing.The main results were as follows:Precipitation changes in early winter or early spring did not affect the winter or spring mean soil temperature and soil respiration.30%precipitation reduction in early winter reduced winter mean soil moisture.30%precipitation increase in early spring significantly increased spring mean soil moisture.Annual mean soil respiration was from 2.34-3.09μmol m^-2S^-1.Compared with natural precipitation treatment,30%precipitation reduction in early winter increased annual mean soil respiration by 13.84%significantly,and 30%precipitation reduction in early spring reduced the annual mean soil respiration by1.85%.The precipitation changes in early winter or early spring did not affect the annual soil temperature.The change of precipitation in early winter had no significant effect on the interannual soil moisture,while the change of precipitation in early spring had significant effect on the interannual soil moisture.The precipitation changes in early winter affected soil nutrients,microbial biomass carbon and microbial PLFAs significantly.30%precipitation reduction in early winter significantly enhanced microbial biomass carbon and microbial PLFAs and the ratio of dissolved organic carbon to available nitrogen.30%precipitation increase in early winter only increased the ratio of dissolved organic carbon to available nitrogen.Compared with natural precipitation,30%precipitation reduction in early spring increased soil total PLFAs,bacterial PLFAs,fungal PLFAs and AMF PLFAs.The soil temperature single-factor model explained 30.6%-47.8%of soil respiration changes,and precipitation changes in early winter increased the temperature sensitivity of soil respiration.Soil temperature and moisture linear model explained soil respiration changes by 20.5%-41.1%.The two-factor index model of soil temperature and moisture explained 16.4%-34.9%of soil respiration variation.Soil respiration was positively related to soil temperature,available phosphorus,soil microbial PLFAs（total PLFAs,fungal PLFAs and AMF PLFAs）,and was a significant negative correlation with the ammonium content in soil.Compared natural precipitation,the annual soil CO₂emission was significantly higher under 30%water reduction in early winter and 30%water reduction in early winter and 30%water reduction in early spring.Precipitation changes in special seasons can have a great impact on the annual soil CO₂emissions,even though they have little impact on the annual cumulative precipitation.These results suggest that the timing of precipitation may be a more important factor than precipitation in the assessment of annual soil respiration in north subtropical and warm temperate forest ecosystems.This process mainly due to non-linear response of soil moisture to precipitation and microbial community activity.The above research results showed that effects of precipitation changes in different precipitation timing on soil CO₂emissions are asymmetrical.In the prediction of soil carbon cycling under precipitation changes of different timing,precipitation change timing should be fully considered.