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Urbanization has progressively intensified over the past few decades, transforming the structure and function of urban ecosystems and influencing the concentrations and spatial distributions of phosphorus (P) in the soil. This study collected 177 surface soil samples (to a depth of 20 cm) to understand the dynamics of soil P along a gradient of urbanization from a densely urbanized central city to less human-affected suburbs to a new exurban satellite in Chengdu, China. The results showed that concentrations of soil total P (TP) and its fractions (except Water-Po, NaOH-Pi, and Residual-P) in the central city and exurban satellite were significantly higher than in suburban areas ( p  < 0.05). Meanwhile, the concentrations of soil TP and its fractions (except Residual-P) significantly decreased with the increase in distance from the urban center ( p  < 0.05). These concentrations were significantly positively correlated with the densities of built-up areas and roads, and showed significant differences among different green space types. The results of generalized linear models indicated that the most decisive factors contributing to TP accumulation were the distance from urban center and green space type. Generally, green space type and density of built-up area were likely to be more crucial determinants governing soil inorganic P fractions compared with other factors, whereas the key factors affecting soil organic P fractions were varied. To conclude, urbanization is likely to lead to the accumulation of P and, thus, controlling the expansion of built-up areas and road areas is necessary to alleviate soil P accumulation in urban systems. [ABSTRACT FROM AUTHOR]

Complex and dynamic land-use patterns have been observed globally due to rapid urbanization and persistent human disturbance. Analyzing the effect of urbanization on carbon (C) stocks is a key step toward enhancing C sequestration and mitigating emissions of carbon dioxide. In a newly urbanized area of western Chengdu, China, we analyzed soil organic C (SOC), soil inorganic C (SIC) stocks down to 1 m, and aboveground vegetation C, and we discussed the effects of land use, density of construction and roads, and distance from the urban center on SOC and SIC density. The SOC, SIC stocks down to 1 m, and aboveground vegetation C stocks were 1.08 × 10 9 kg, 4.67 × 10 7 kg, and 1.58 × 10 7 kg, respectively. Our analyses of SOC and SIC density provided three results: (1) it was significantly higher in rural than in urban land-use types; (2) it tended to decrease as the density of construction and roads increased; and (3) it increased with distance far from the urban center. The results indicated that urbanization led to SOC and SIC loss in our study area. SOC and SIC loss will be alleviated by decreasing the construction and road density and increasing green space area. [ABSTRACT FROM AUTHOR]

Soil labile organic carbon fractions (LOCF) are valuable indicators of changes in soil quality and soil total organic carbon (TOC), and they are easily influenced by changes in soil management practice. To explore the sensitivity of LOCF and their enzymatic conversion under straw mulch for scientific management of crop straw use on the Chengdu plain, a straw mulch field experiment was conducted to observe the LOCF changes and explore their relationships with C-cycle enzymes during wheat growth. The treatments included no fertilizer or straw (Control), only mineral fertilizer (MF), 10% rice straw nitrogen (N) plus 90% fertilizer N (RS1), 20% rice straw N plus 80% fertilizer N (RS2), 30% rice straw N plus 70% fertilizer N (RS3), 100% rice straw (RS). The water-soluble organic carbon (WSOC) and microbial biomass carbon (MBC) under straw treatments in the 0–20 cm soil layer were significantly higher than those of Control and MF treatments from the seedling stage, and showed significant differences among straw treatments from the tillering stage. Correspondingly, the dissolved organic carbon (DOC) and permanganate oxidized carbon (POXC) showed no obvious differences among straw treatments in most growth stages. Therefore, WSOC and MBC were the most sensitive indicators for assessing soil organic carbon (SOC) change under straw mulch. Moreover, stepwise multiple linear regression revealed that cellulase and β-glucosidase were significantly positive impact factors for LOCF in the two soil layers, while polyphenol oxidase had both positive and negative impacts on WSOC at different soil layers, and peroxidase was a negative factor for LOCF. [ABSTRACT FROM AUTHOR]