Photosynthetic characteristics, leaf anatomy, and shade tolerance evaluation of three wild Ranunculaceae groundcovers under shading

Three wild Ranunculaceae groundcovers, Anemone cathayensis, A. flaccida, and Pulsatilla cernua, were investigated under full sunlight and four shading levels (30%, 50%, 70%, and 90%). Photosynthetic characteristics, chlorophyll fluorescence kinetics, and leaf anatomy were measured, and shade tolerance was comprehensively evaluated by principal component analysis and the membership function method. Under shading, common adaptive responses included increased photosynthetic pigments and decreased stomatal density and leaf thickness, which enhanced light capture and reduced construction cost, resulting in higher apparent quantum efficiency (AQY) and maximum net photosynthetic rate (Pnmax) and a lower light compensation point (LCP). Chlorophyll fluorescence revealed reduced photosystem II (PSII) thermal dissipation and enhanced primary quinone acceptor (QA) reoxidation and acceptor-side electron transport. Interspecific differences were also observed: the chlorophyll/carotenoid (Chl/Car) ratio generally remained unchanged in A. cathayensis and P. cernua, and increased in A. flaccida. A. cathayensis showed increased light saturation point (LSP) and dark respiration rate (Rd), unchanged palisade/spongy ratio (P/S), generally stable absorbed energy per reaction center (ABS/RC) but increased trapped energy (TRo/RC), and elevated total performance index (PItotal). Both A. flaccida and P. cernua lowered LSP and Rd and decreased P/S. Notably, A. flaccida exhibited higher oxygen-evolving complex activity and plastoquinone pool capacity, reduced ABS/RC and TRo/RC, and increased PItotal, whereas P. cernua increased both ABS/RC and TRo/RC with unchanged PItotal. Comprehensive evaluation ranked A. flaccida as the most shade-tolerant species, suggesting its potential in shaded environments. These findings were obtained under potted controlled conditions and caution is needed when extrapolating to field conditions.