Size Variation in Flower Petals of Chinese Animal-Pollinated Plants in Response to Climatic and Altitudinal Gradients

The evolutionary adaptations of plant reproductive structures, including angiosperm petal size, are driven by a combination of natural selection influenced by ecological conditions. While previous studies have emphasized pollinator-driven selection on petal traits, significant gaps remain in understanding how abiotic factors, biotic interactions, and life-history trade-offs jointly shape petal size across broad environmental gradients. This study integrates macrogeographic analyses of 10,228 animal-pollinated angiosperm species across China's diverse climatic regions, combining trait data from national flora databases, species distribution records, and high-resolution climate variables. Using hierarchical regression, variance partitioning, and threshold detection models, we disentangle the effects of altitude, latitude, temperature, and precipitation on absolute petal size and its ratio to plant height (MR), while contrasting woody and herbaceous life histories. Key findings reveal: (1) nonlinear thresholds in environmental drivers, with herbaceous petal size declining sharply above 3200 m altitude and 1100 mm annual precipitation; (2) altitude as the dominant predictor of MR, explaining 30% of variance, particularly in alpine zones where floral conspicuousness increases despite plant dwarfing; (3) divergent strategies between woody and herbaceous species, where woody plants prioritize absolute petal size in warm climates, while herbaceous species amplify MR under high-altitude stress; and (4) climate-geography interactions explaining 62%-71% of trait variation, highlighting context-dependent trade-offs between pollinator attraction and stress tolerance. This work provides a comprehensive framework linking petal size traits to multivariate environmental gradients at continental scales, offering critical insights into plant adaptive strategies under climate change and emphasizing altitude-mediated selection as a key driver of floral diversity.