Quantifying and mapping threats to soil biodiversity in Nanjing, China

- A framework of multiple factors affecting soil biodiversity was proposed.
- Composite threats to soil biodiversity decreased with distance from the city centre.
- Soil pollution was the biggest threat to soil biodiversity in Nanjing.
- The main threats to soil biodiversity can used to guide urban planning.

As one of the largest biodiversity pools, soil biodiversity is affecting ecosystem services significantly. However, soil biodiversity is hidden below ground and has often been overlooked. It is extremely urgent for us to protect soil biodiversity. Here, we briefly illustrate the relationship among factors affecting soil biodiversity and the mechanisms of these factors influencing soil diversity. After evaluating seven factors expected to affect soil biodiversity (land-use change, organic carbon loss, agriculture/land-use intensity, soil erosion, soil compaction and sealing, soil pollution and soil acidification), we quantified and mapped the composite threats to soil biodiversity in Nanjing using a weighted sum method. The correlative relationships between the composite threats index and the seven factors were also used to identify the main threats to soil biodiversity. We found that threats to soil biodiversity generally decreased with distance from the city centre. Soil pollution, agriculture/land-use intensity and soil compaction were the main threats to soil biodiversity in Nanjing. Some suggestions for urban planning are also tentatively provided based on the main threats to soil biodiversity in urban, suburban and rural areas. The quantification of threats to soil biodiversity can provide a useful tool for decision-making and improving ecosystem services.