Nematode diversity loss and community change in urban green spaces explained by alterations in soil pore structure and chemical properties

• Micro-computed tomography reveals detailed soil pore characteristics in urban environments versus forests. • Urban green spaces exhibit significant soil porosity reduction affecting nematode communities. • Soil pore structure alterations critically influence nematode diversity beyond chemical property changes. • Increased urbanization correlates with decreased nematode community richness and altered composition. • Enhancing soil porosity can promote healthier nematode communities and urban ecological resilience. Due to various urban stressors, urban green spaces often fail to maintain soil biodiversity when compared to natural forests. Previous studies attributed this reduction to chemical changes in the soil. However, many human activities in urban environments can lead to soil compaction and changes in soil pore structure, which have been poorly investigated. Here, we compared the diversity of nematode communities, a key indicator of soil health, in soils collected from natural forests and urban green spaces (parks and green belts). We characterized pore structures using micro-computed tomography (Micro-CT) alongside chemical properties, to assess the contribution of these soil changes to variations in nematode communities. Our findings revealed significant changes in soil chemical properties (mainly in soil pH) and a substantial loss of soil porosity by 84.88 % in urban green spaces, accompanied by fragmentation of the morphology of habitable pore space. Specifically, the volume of soil pores decreased by over 95 %, with a decline in the proportion of macropores (over 79 %) and a more than 160 % increase in mesopores. These physical alterations, driven by urbanization intensity, negatively affected nematode communities, leading to significant declines in community diversity, shifts in community composition, and reduced network complexity. Importantly, changes in soil pore structure were as critical as chemical properties in explaining the effects of urbanization on nematodes. This study provides guidance for urban planning and management, focusing on improving soil chemical and physical characteristics to preserve soil biodiversity and ecological resilience in urban environments.