Functional traits from pollen and plant assemblages show complex relationships on the Tibetan Plateau: A deep insight into plant functional paleoecology

Functional paleoecology offers a novel approach that bridges the gap between Quaternary paleoecology and modern ecology, but the feasibility of applying functional trait-based approaches to pollen data remains underexplored. In this study, we compiled datasets of plant communities, plant functional traits, and pollen counts obtained from 207 sites across the Tibetan Plateau to evaluate the accuracy of pollen-based functional traits in reflecting functional trait composition and functional diversity within their surrounding plant communities. Our findings reveal that, across the broad scale of the entire study area, community-weighted means (CWMs) of each plant functional trait estimated from pollen data show significant correlations with those estimated from plant assemblages. However, this conclusion does not apply uniformly to all vegetation types. For instance, in alpine meadow, leaf thickness (LT), specific leaf area (SLA), leaf nitrogen content (LNC), and leaf phosphorus content (LPC) show non-significant correlations between CWMs derived from pollen data and those derived from plant assemblages. Functional diversity indices (FDs) generally show very weak correlations (R² < 0.2) between pollen- and plant-based estimations, with the exception of functional richness, which displays significant correlations across the entire study area (regardless of vegetation type) and in four of the seven vegetation types analyzed. The results demonstrate that both the pollen-inferred CWMs of plant functional traits and pollen-inferred FDs show significant correlations with temperature and precipitation. However, only LT, LPC, and functional divergence estimated from pollen assemblages adequately capture the trends in plant-derived CWMs and FDs along temperature and precipitation gradients. Our study underscores the potential of pollen data for reconstructing temporal trends in plant functional traits through the integration of functional trait approaches. Nevertheless, the application of plant functional paleoecology necessitates careful selection of functional traits and functional diversity indices, as well as a consideration of vegetation context when interpreting changes in pollen-inferred functional trait composition and functional diversity.