Study on the differences in leaf traits between tropical-subtropical cycad gymnosperms and woody angiosperms

Cycads, the oldest living seed plants, are primarily distributed in tropical and subtropical regions and are critically endangered. Comparative analysis of leaf traits between tropical-subtropical gymnosperm cycads and woody angiosperms offers valuable insights into the ecological strategies of cycad species. This study measured the morphological, anatomical, and hydraulic characteristics of leaves (pinnae) from 28 cycad species in the Nanning Botanical Garden. In addition, leaf traits of 79 tropical-subtropical forest tree species were compiled for comparative analysis. Results showed that: (1) Compared to angiosperms, cycads exhibited thicker leaves, higher saturated water content (SWC), stronger resistance to water loss (Ψ_tlp), and lower specific leaf area (SLA) and stomatal density (SD). However, the differences in leaf tissue thickness (MT) between the two taxa were not significant. (2) The network edge density (ED) of leaf traits in angiosperms was significantly higher than in cycads, while angiosperms showed lower network diameter and average path length. This indicates stronger correlations among angiosperm traits, facilitating more efficient resource utilization in tropical and subtropical environments. (3) Unlike angiosperms, SLA and Ψ_tlp in cycads were decoupled from SWC, suggesting that cycads rely more on water uptake through root systems or storage in stems rather than fine-tuning leaf physical properties for water regulation. This study highlights the variability and diversity of adaptive strategies across plant taxa and provides insights into the unique ecological adaptations of cycads in tropical and subtropical environments.