Urban development enhances soil organic carbon storage through increasing urban vegetation

Global distribution of surface soil organic carbon in urban greenspaces

Urban greenspaces continue to grow with global urbanization. The global distribution and stock of soil organic carbon (SOC) in urban greenspaces remain largely undescribed and missing in global carbon (C) budgets. Here, we synthesize data of 420 observations from 257 cities in 52 countries to evaluate the global pattern of surface SOC density (0-20 cm depth) in urban greenspaces. Surface SOC density in urban greenspaces increases significantly at higher latitudes and decreases significantly with higher mean annual temperature, stronger temperature and precipitation seasonality, as well as lower urban greenness index. By mapping surface SOC density using a random forest model, we estimate an average SOC density of 55.2 (51.9-58.6) Mg C ha-1 and a SOC stock of 1.46 (1.37-1.54) Pg C in global urban greenspaces. Our findings present a comprehensive assessment of SOC in global urban greenspaces and provide a baseline for future urban soil C assessment under continuing urbanization.

Impact of anthropogenic land uses on soil microbiological activity in a peri-urban landscape

Land use and land cover patterns impact soil properties and negatively affect soil microbial community and related processes. However, the information regarding the influence of urban land use on soil microbial composition and functioning is limited. Here, we investigated the impact of urban land use patterns on soil microbiological parameters by comparing five contrasting anthropogenic land use classes, i.e. agriculture, park, roadside plantation, street green, and bare land. Soil physicochemical properties, basal respiration (BR), microbial biomass carbon (MBC), and enzyme activities were estimated and correlated. The results revealed that soil physicochemical and microbiological properties greatly varied across the five land use classes. Among all the land use types, the roadside plantation had the highest nutrient content, i.e. soil organic carbon (SOC), total nitrogen (TN), and mineral nitrogen (MN) (1.33%, 0.13%, 84.0 mg kg-1, respectively), while the soil functional capacities measured in terms of BR, MBC, microbial quotient (QCO2), soil microbial activity (SMA), and dehydrogenase activity (DHA) (9.90 C µg g-1 h-1, 300 µg g-1, 0.045 µg h-1/ µg MBC, 9.0 µg ml-1, 1.30 TPF g-1 h-1, respectively) were highest in the park. Disturbed street greens were markedly nutrient depleted and apparently exhibited lower microbial activity. Variations in soil BR, MBC, and enzyme activity were revealed to be primarily influenced by soil moisture, available phosphorus, and SOC content. We concluded that the negative impacts of anthropogenic land use soil quality and microbiological functioning can be managed by integrating proper management approaches for various land use classes in urban systems.

Urban-rural disparities of carbon storage dynamics in China's human settlements driven by population and economic growth

China has experienced a rapid expansion of human settlement in both urban and rural areas over the past three decades. Regarding the impacts on carbon storage, previous studies that only focus on certain ecosystems cannot reflect urban-rural disparities, resulting in the carbon storage changes in human settlement remaining unknown. In this study, we aimed to explore China's urban-rural disparities in human settlement expansion and direct impacts on carbon storage by using the big Earth data technology. The results showed that from 1990 to 2018, the total amount of China's human settlement expansion reached 175,703.80 km², and the inner-city, peri-urban, and rural components accounted for 21.00 %, 20.18 %, and 58.82 %, respectively. Along with the general tendency of impervious surface area (ISA) growth, there was more soil organic carbon (SOC) (1254.33 TgC) being sealed beneath ISA (0-100 cm depth), compared to a huge reduction in vegetation biomass carbon (VBC) (91.44 TgC) during the study period. The results further indicated that the change density of either VBC or SOC presented a slightly rising trend along the urban-rural gradient, due to the increasingly common encroachment on vegetation and soil types with higher carbon content. We also found that socioeconomic drivers had a greater influence in urban areas than rural areas, and the related correlation exhibited a descending trajectory in both urban and rural areas. There is thus an urgent need to preserve lands with abundant carbon storage and contain the waste of land resources in rural areas. All stakeholders should pay more attention to concerted and targeted regulation policies for well-planned and eco-friendly human settlement expansion such as enhancing rural land use efficiency and promoting large-scale afforestation and continuous urban greening, which will be critical not only for guiding sustainable urbanization all over China but also for mitigating climate change for the entire world.

Sediment organic carbon dynamics response to land use change in diverse watershed anthropogenic activities

Sediment organic carbon (SOC) is a precious archive that synthesizes anthropogenic processes that remove geochemical fluxes from watersheds. However, the scarcity of inspection about the dynamic mechanisms of anthropogenic activities on SOC limits understanding into how key human factors drive carbon dynamics. Here, four typical basins with similar natural but significantly diverse human contexts (high-moderate-low disturbance: XJ-ZS and YJ-LS) were selected to reconstruct sedimentation rates (SR) and SOC dynamics nearly a century based on 200-cm corers. A partial least squares path model (PLS-PM) was used to establish successive (70 years) and multiple anthropogenic data (population, agriculture, land use, etc.) quantification methods for SOC. Intensified anthropogenic disturbances shifted all SR from pre-stable to post-1960s fluctuating increases (total coefficient: high: 0.63 < low: 0.47 < medium: 0.45). Although land use change was co-critical driver of SOC variations, their trend and extent differed under the dams and other disturbances (SOC mutated in high-moderate but stable in low). For high basin, land use changes increased (0.12) but dams reduced (-0.10) the downstream SOC. Furthermore, SOC mutation corresponded to soil erosion due to urbanization in both periods A and B. For moderate, SOC was reversed with the increase in afforestation and cropland (-0.19) due to the forest excitation effect and deep ploughing, which corresponded to the drought in phase B and the anthropogenic ecological project in A. For low, the increase in SOC corresponded to the Great Leap Forward deforestation in period B and the reed sweep in A, which suggested the minor land change substantially affected (0.16) SOC in fragile environments. Overall, SOC dynamics revealed that anthropogenic activities affected terrestrial and aquatic ecosystems for near the centenary, especially land use. This is constructive for agroforestry management and reservoir construction, consistent with expectations like upstream carbon sequestration and downstream carbon stabilization.

Spatio-Temporal Variation and Its Driving Forces of Soil Organic Carbon along an Urban-Rural Gradient: A Case Study of Beijing

Rapid urbanization has reshaped land cover and the ecological environment, potentially improving or deteriorating soil organic carbon (SOC). However, the response of SOC to urbanization has not yet been fully exploited. Herein, by using the land-use transfer matrix, the Sen & Mann-Kendall tests, the Hurst index, and a geographical and temporal weighted regression (GTWR) model, as well as an urban-rural gradient perspective, we assessed the dynamic response of SOC to Beijing's urbanization from 2001 to2015 and identified the main drivers. The results found that SOC stock decreased by 7651.50 t C during the study period. SOC density varied significantly along an urban-rural gradient, with high value areas mainly being located in remote mountainous rural areas and low value areas mainly being located in urban areas on the plains. There was an uneven variation in SOC density across the urban-rural gradient, with suburban areas (25-40 km away from urban cores) losing the most SOC density while urban areas and rural areas remained relatively unchanged. GTWR model revealed the spatio-temporal non-flat stability of various driving forces. Precipitation, the proportion of forest, the proportion of grassland, the population, distance to the urban center, the slope, and the silt content are the main factors related to SOC stock change. As a result, we suggest policy makers reconceptualize the uneven variation in the SOC between urban and rural areas, emphasize suburban areas as a target for controlling SOC loss, and take into consideration the spatial and temporal heterogeneity of the factors influencing SOC stock when evaluating policies.