Contrasting whole-plant hydraulic strategies between light-demanding and shade-tolerant tropical-subtropical ferns

BACKGROUND AND AIMS: Ferns are one of the most diverse lineages of vascular plants, distributed widely in various habitats of tropical and subtropical forests. Previous studies have indicated that ferns tend to operate conservative stomatal behavior. However, this finding is difficult to explain the abundant fern species in open sites. This study aimed to clarify a whole-plant hydraulic strategy of tropical-subtropical ferns with different light requirements. METHODS: We selected a total of 26 terrestrial fern species (14 light-demanding species and 12 shade-tolerant species) from the tropical-subtropical forests and measured their root (specific root length, SRL), stem (rhizome; rhizome biomass fraction, RHMF), and leaf hydraulic (pinna; hydraulic efficiency, drought tolerance, minimum leaf water potential, and safety margin) traits. In addition, we compiled a dataset of leaf hydraulic traits for woody and herbaceous angiosperm species from literatures. We analyzed the differences in safety margin between ferns and angiosperms, the root-stem-leaf traits relationships, and the contrasting whole-plant hydraulic strategies between light-demanding and shade-tolerant fern species. KEY RESULTS: On average, ferns had more negative stomatal safety margin than woody and herbaceous angiosperm species. In addition, ferns showed lower leaf hydraulic safety margin than woody angiosperms. Below-ground traits significantly influenced leaf hydraulic safety in ferns, that is, species with lower SRL and higher RHMF showed higher water potential and leaf hydraulic safety margin. Compared to fern species from shade understory, light-demanding species were associated with higher SRL, lower RHMF, and higher leaf hydraulic risk. CONCLUSIONS: We conclude that tropical-subtropical ferns do not exhibit conservative leaf-level hydraulics but rely on a whole-plant strategy involving root acquisition and rhizome storage, which underlies their contrasting performance across light and water availability. This integrative view is crucial for predicting fern responses to habitat disturbance and climate change.

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