Distribution characteristics and influencing factors of soil CO2 in different land use patterns in loess hilly region in summer

The Loess Plateau has a deep soil layer and contains a huge inorganic carbon pool. In order to understand the effects of different land use patterns on soil CO2 content, the physical and chemical properties of soil from different land use types (fruit trees, field crops, wasteland) and the CO2 distribution characteristics and their influencing factors at different depths of soil in the loess hilly region were analyzed. The results showed that there were no significant differences in total phosphorus and total potassium content in three different land use types of fruit trees land, field crops land and wasteland. The contents of soil organic carbon has the order of field crops land (2.95±1.19 g·kg-1) > wasteland (2.63±1.36 g·kg-1) >fruit woodland (2.38±0.78 g·kg-1), while the content of soil inorganic carbon has the order of field crop land (14.36±5.17 g·kg-1) > fruit woodland (14.16±1.32 g·kg-1) > wasteland (12.40±4.04 g·kg-1). Similarly, soil total nitrogen content is highest in field crops land , and the other two land use patterns have roughly the same total nitrogen content. Different land use types have a great impact on the CO2 volume fraction of the soil profile. The soil CO2 content in the depth of 0-20 cm in the fruit trees land is higher than that in the field crops land and wasteland. The reason for this is that on the one hand, the surface of the fruit trees land has more litter, and the surface organic carbon results in a large amount of CO2 under the action of microbial decomposition; On the other hand, the artificial disturbance of fruit trees land is small, while the field crops land are highly disturbed. The concentration of CO2 in soil depends to a greater extent on the management practices of cropland and the varieties of crops. The soil CO2 content in the soil at 80 cm in the three land use patterns suddenly decreased, which may be caused by the absorption of soil CO2 by rainwater infiltration and the action of lower carbonate minerals. That is, the dissolution process of carbonate minerals consumes soil CO2. Soil temperature and humidity all affected the production of soil CO2 to some extent, but the correlation was not significant. The reason is that soil respiration response in the study area is highly dependent on soil water content, and the rate of soil CO2 production is more affected by the coupling of hydro-thermal factors.