Effects of litter addition from common greening tree species in northern China on organic carbon composition characteristics of urban soils

This study aimed to establish a scientific basis for the utilization of litter from greening tree species to enhance the content and composition characteristics of urban soils. As such, litter from eight common greening tree species, including Salix babylonica L., Acer pictum subsp. mono (Maxim.) H. Ohashi, Ginkgo biloba L., Sophora japonica L. var. japonica f. pendula Hort., Pinus tabuliformis Carrière, Juniperus formosana Hayata, Platycladus orientalis (L.) Franco, and Picea asperata Mast., was collected. The litter was then mixed with the disturbed surface soil from urban areas of Yan’an City at a 2% ratio (litter/soil, dry weight) and incubated for 120 d under conditions simulating natural soil density and moisture levels. Subsequently, changes in soil organic carbon, its components, and carbon pool indices were analyzed, along with their relationships with the chemical properties of the litter. Results revealed significant increases in soil organic carbon content with the addition of most litters, except for A. pictum subsp. mono and J. formosana, as well as significantly increased stable component content from other species except A. pictum subsp. mono, G. biloba, and J. formosana, with nearly all types of litter also markedly enhancing the moderately and highly activated components. In addition, treatment with S. babylonica, P. orientalis, P. asperata, and P. tabuliformis litter significantly increased the carbon pool index of the soil, with nearly all types of litter significantly increasing the lability index and carbon pool management indices of soil, but only P. orientalis litter treatment significantly increasing the carbon recalcitrant index. Correlation analysis identified negative associations between the levels of litter N and amino acids and both the content and components of soil organic carbon, as well as positive correlations between litter total phenols, soluble sugars, and C to N, C to P, and N to P ratios with the soil content of highly/slightly activated and stable carbons. Additionally, the content of litter organic acids, P, C, terpenes, phenols, and the C to N ratio exhibited positive relationships with moderately activated carbons in soil. To enhance the content, activity, and stability of organic carbon in urban soil, P. orientalis litter may be the preferred soil amendment, followed by litter from S. babylonica, P. asperata, and P. tabuliformis.