Impact of lithology on protist diversity and community composition in Southwest China: Insights from forests and croplands

Protists are commonly considered to be drivers of soil microbial functional groups in terrestrial ecosystems. Although the impact of land use intensity on protist diversity and community composition has been well reported, the response of the protist community to different lithologies is less well understood. We conducted field sampling in forests restored for at least 60 years and long-term maize-cultivated croplands as control, assessing protist diversity, community composition, and interaction patterns in response to lithology across temperature gradients (with temperature differences exceeding 9 °C). In limestone, protist richness in forests and croplands was 22.1 % and 16.4 % significantly (one-way ANOVA, p < 0.05) higher, respectively, than in clastic rock. In croplands, compared to forests, protist richness, Shannon index, and Simpson index were 39.7 %, 24.7 %, and 6.6 % significantly (one-way ANOVA, p < 0.05) higher over limestone and 46.5 %, 20.8 %, and 4.5 % significantly (one-way ANOVA, p < 0.05) higher over clastic rock, respectively. These variations are associated with soil properties, such as soil pH and Ca2+ content. In limestone forest soils, the relative abundance of Cercozoa decreased while Lobosa increased with rising mean annual temperature, indicating their different adaptations to increasing temperature. Limestone exhibited more complex co-occurrence networks than clastic rock in forest environments, suggesting greater stability. This phenomenon is attributed to the crucial role of Apicomplexa, Cercozoa, Conosa, Lobosa, and Ochrophyta, which exhibited numerous connections to other groups in different ecosystems. Future functional studies on protists in fragile ecosystems, together with other microbiomes, carry significant implications for the region's resilience to climate change and the sustainability of ecological restoration efforts.