Phylogenetic relationships versus environmental impacts on the distribution and traits of Laureae (Lauraceae) species within and outside karst tiankengs

Premise

A karst tiankeng, a unique sinkhole-like terrain with a rare and distinctive habitat, is often likened to an isolated island because of its limited contact with the external environment. This distinctive landscape potentially shapes the evolution and distribution of the associated plant species. However, the relative contributions of environmental impacts versus phylogenetic relationships in shaping plant adaptations to the tiankeng environment remain unclear. We analyzed trait divergence within Laureae, a dominant group in a tiankeng forest, to discern whether trait variations among Laureae populations within and outside the tiankeng were shaped predominantly by environmental influences or phylogenetic heritage.

Methods

We reconstructed a phylogenetic tree for Laureae within and beyond the Baise Tiankengs using plastid genomes to estimate dispersal times, trace ancestral distributions, and model distributional shifts under various climatic scenarios. We also compared leaf and fruit traits of plants within and outside the tiankeng.

Results

The uplift of the Qinghai-Tibet Plateau affected the climate in South China, shaping Laureae traits. A discernible phylogenetic signal indicated environmental factors significantly drive trait variations in Laureae in the tiankeng. A markedly smaller leaf length/width ratio endows the Laureae populations in the tiankeng with enhanced resilience to colder microclimates compared to populations in surrounding areas. Maximum and minimum leaf length/width ratios were also significantly lower in the tiankeng.

Conclusions

These findings advance our understanding on biodiversity and plant trait divergence inside tiankengs, underscoring the importance of preserving unique habitats and restoring vegetation in these terrains.