Effects of Tiankeng topography on ecological strategy of karst evergreen and deciduous broad-leaved mixed forest

Tiankeng negative topography is a magnificent landscape located in karst evergreen and deciduous broad-leaved mixed forests. It has garnered increasing attention due to its geomorphological features, natural species refuge, and biodiversity conservation. Given its unique nature, it is likely that ecological strategy for resource allocation, key factors influencing species strategies, and underlying coexistence mechanisms of species in this habitat may differ from those found in general karst forests. Thus, we established three types of forest plots (The inside of Tiankeng forest, the fringe of Tiankeng forest and nearby typical karst forest) on two contrasting topographies (Tiankeng and mountain) and measured plant leaf functional traits and soil characteristics in a karst evergreen and deciduous broad-leaved mixed forest of southwest China. Based on measurements of leaf area, leaf dry matter content and specific leaf area in the "StrateFy" tool, we compared the effects of variations in ecological strategy by using Grime's competitor (C), stress-tolerator (S), and ruderal (R) theory. The results showed that unique species in the inside of Tiankeng forests were 10.87%-17.98% higher than those in the nearby karst forests, and the soil phosphorus in the inside of Tiankeng forests was significantly higher than those in the nearby karst forests (P < 0.05). CSR strategies components were significantly different in the three forests. The component C and R in the inside of Tiankeng forests were higher than that in fringe of Tiankeng forests and nearby karst forests, indicating that the inside of Tiankeng forests can recruit more C-and R-selected species from the nearby forests. Furthermore, Tiankeng negative topography affected the distribution of species CSR strategy by altering soil characteristics, and the soil total phosphorus was the principal driver of species ecological strategy in the inside of Tiankeng forests. Our findings highlight the naturalness and specificity of Tiankeng species in evergreen and deciduous broad-leaved mixed forests, and differentiation in ecological strategy maybe one mechanism facilitates species coexistence. We suggest that the conservation of Tiankeng should not only focus on in-situ preservation of biodiversity but also consider the role of nearby karst forests in promoting sustainable development of Tiankeng.