Chlorophyll fluorescence traits reveal ecological specialization of plant species through photosynthetic functional syndromes

Abstract

Photosynthesis represents a fundamental interface between plants and their environment, integrating resource acquisition, stress tolerance, and ecological adaptation. Although chlorophyll fluorescence analysis has become a widely used method for assessing photosystem II (PSII) function under environmental stress, its potential for comparative ecological studies and trait-based interpretation remains insufficiently explored. In particular, it remains unclear whether stable interspecific variation in OJIP chlorophyll fluorescence reflects long-term ecological specialisation rather than merely short-term physiological responses. This study investigated whether OJIP fluorescence parameters can be interpreted as species-level functional traits associated with ecological differentiation among vascular plants. Chlorophyll fluorescence measurements were obtained for a broad range of plant species and analysed alongside ecological indicator values describing species’ preferences for light, temperature, moisture, soil pH, and nutrient availability, as well as plant ecological strategies based on Grime’s CSR framework and species hemeroby. Multivariate relationships between fluorescence traits and ecological characteristics were evaluated using constrained ordination to identify environmentally structured components of PSII functional variation. The results demonstrated that interspecific diffe r ences in chlorophyll fluorescence were associated with species’ ecological specialisation. OJIP parameters formed coordinated functional profiles rather than independent responses of individual variables, indicating that ecological differentiation is expressed through integrated patterns of PSII energy absorption, excitation trapping, electron transport, reaction centre density, and energy dissipation. Species associated with open, high-light habitats exhibited fluorescence characteristics consistent with enhanced photoprotective regulation and increased excitation pressure, reflecting adaptation to excessive irradiance. In contrast, species from more humid, nutrient-rich habitats displayed profiles associated with higher photochemical efficiency and greater functional capacity of PSII reaction centres, suggesting optimisation for effective utilisation of limited and heterogeneous light conditions within dense vegetation. The ecological interpretation of fluorescence traits was further supported by their relationships with disturbance affinity and plant ecological strategies. Ruderal and highly hemerobic species were characterised by fluorescence profiles reflecting dynamic regulation of excitation energy and electron transport, whereas species with contrasting stress-tolerant or competitive strategies showed distinct patterns of PSII organisation. The constrained ordination approach demonstrated that environmentally related variation in OJIP parameters represents a specific component of total fluorescence variability, separating ecologically meaningful signals from variation associated with other factors such as phenology, ontogeny, genetic differentiation, and phylogenetic history. These findings support the interpretation of OJIP chlorophyll fluorescence parameters as functional traits describing species-level differences in photosynthetic organisation. By linking PSII function with ecological specialisation, OJIP-based traits provide a physiological dimension for comparative plant ecology and expand the application of chlorophyll fluorescence from stress assessment towards the analysis of plant functional strategies across environmental gradients.