| As an important part of global greenhouse gas,CO2 released by soil respiration has a far-reaching impact on global climate change.With the implementation of ecological civilization construction in loess plateau area,the land use changed,and then the hydrothermal condition and litter fall condition indirectly influenced the contribution of soil respiration to atmospheric CO2.Therefore,soil respiration and carbon source has a great significance for estimating the impact of ecological construction on the carbon balance in this region.Through selecting the soil of 5 kinds of typical land use in loess hilly-gully region as the research object,and adopting the combined method of field dynamic monitoring and laboratory experiments,the impact of soil respiration rate change and litter fall on CO2 released by soil respiration under different soil utilization in dry season and rainy season is analyzed.The law of carbon release in the soil respiration process is also revealed,and then the contribution ratio of carbon source of soil respiration is quantitatively calculated through the stable carbon isotope technology.The main conclusions are as follows:(1)The diurnal variation law that different lands use soil respiration rate is basically consistent,presenting a single peak curve,and the low peak and high peak value are at 2:00-5:00 and 11:00-14:00 respectively.The daily mean value of soil respiration rate in dry season is:shrub land>slope cropland>forest land>orchard>grassland.But in rainy season:grassland>forest land>shrub land>slope cropland>orchard.The daily mean value of soil respiration rate of each land(0.14?6.51 u mol·m-2?s-1)in rainy season is significantly higher than that in dry season(0.13?1.33 umol·m-2·s-1).(2)In 5 cm of surface soil,the main factors of affecting soil respiration are soil temperature and moisture,and there is a significant positive correlation between soil respiration rate and 5-cm soil temperature(P<0.05).Meanwhile,there is a negative correlation between soil respiration rate and 5-cm soil moisture(P<0.05).In addition,soil temperature single factor model.The resolution of soil temperature of different land use to diurnal variations of soil respiration in the dry season(44.30%?69.20%)is higher than that of soil moisture(7.50%?41.30%),the co-resolution of both to soil respiration is higher than that of soil moisture,and the co-interpretation of soil respiration is higher(56.50%?70.00%).In the rainy season,the soil respiration's temperature sensitivity is higher and the resolution of soil temperature and moisture to diurnal variations of respiration is higher than that of dry season.(3)The litter fall makes the soil respiration rate and temperature sensitivity of the land use change,which significantly weakened the response between soil respiration and soil water.In dry season,litter fall makes soil respiration increase,and makes the composite model fitting R2 value increase,and its contribution to the soil respiration of forest land is the highest(40.45%),followed by shrub land(33.89%),and the grassland is the minimum(22.71%);In rainy season,the contribution rate of litter to soil respiration of grassland is positive(21.88%),but its contribution rate to the soil respiration of shrub land and forest land is negative,and they are respectively-21.49%and-21.60%.The "shielding effect" of litter makes the composite model fitting R2 value of respiration and hydrothermal factor reduce.(4)?13C value of CO2 released by different land use soil respiration has a significant diurnal periodical change,and ?13C is more abundant during the day than at light.In the dry season,?13C value of CO2 released by soil respiration varies from-27.24‰ to-23.08‰,and the daily mean value is:forest land>shrub land>grassland>orchard>slope cropland;In the rainy season,the range of its value varies from-27.98‰ to-23.35‰,while the daily mean value is shrub land>grassland>forest land>orchard>slope cropland,613C value of CO2 released by soil respiration is less than that in the dry season,and the diurnal variations coefficient is smaller,and the dispersion degree of ?13C is also small.(5)The contribution rate of carbon source of soil respiration is determined by stable isotope technology.The carbon source of soil respiration of slope cropland and orchard mainly comes from root system,and the contribution ratio is between 73.79%and 93.76%,and the contribution rate of soil microorganisms is smaller,which is between 6.24%and 26.21%;Most of the carbon emitted from soil respiration is from the contribution of litters originally and directly in grassland,shrub land and forest land,with a ratio of 47.77%to 68.14%. |
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