Functional traits and ecological performance indices in non-vascular photoautotrophs (bryophytes and lichens): Retrospective review and outlook towards a unified ontology

Plant ecologists have demonstrated the usefulness of functional traits in explaining vascular plant community structure and ecosystem functioning. Functional Ttrait-based approaches have been increasingly applied to cryptogams over the last thirty years. However, the application of vascular plant-based traits to non-vascular photoautotrophs cryptogams (NVP; here bryophytes and lichens) remains challenging due to their differing ecophysiological characteristics. Several elements of NVP cryptogam functional ecology do not have parallels in vascular plant ecology, such as traits related to morphology (shoot, ramet or thallus architecture, leaf structure), water relations (poikilohydry, desiccation tolerance), and reproduction (vegetative, spores), as well as the scales (e.g., colony) at which some of these traits are measured. Another issue concerns data availability, with relevant information scattered across the literature and NVPcryptogam trait measurements conducted in a variety of ways that are not always comparable. Here, we propose a hierarchical trait ontology and a thesaurus for NVP present the state-of-the-art on the use of traits in cryptogram research and propose a framework to drive future research. Our literature review resulted in a final corpus of 619 598 articles published between 1967 and 2024. Two hundred thirty-two traits were identified, with the majority (70%) being used as response traits related to growth and reproduction in individual organisms. The number and diversity of attributestraits used in NVP studies have increased markedly over time, resulting in substantial heterogeneity in terminology, definitions, and measurement protocols across the literature. We also found that ecological performance indices (EPs) were frequently treated as traits, highlighting a widespread conceptual confusion that complicates data synthesis and cross-study comparisons. The use of the trait-based approach in vascular plant studies has been supported by the development of standardized centralized definitions, protocols, and databases, a foundation not yet developed for NVPcryptogam research. This Based on this review, we proposes an ontology framework for standardizing structuring NVPcryptogam trait data and definitions. Together with more standardized protocols, we hope this framework will enable the future development of consistent functional trait databases of NVPcryptogams, ultimately advancing our understanding of how traits mediate functions and responses of these organisms in ever-changing environments.