Comparison of the structure and photosynthetic characteristics of different photosynthetic organs in Trapa quadrispinosa Roxb.

The genus Trapa possesses three distinct photosynthetic organs, including submerged leaves, floating leaves, and adventitious roots. In this study, we compared the anatomical structures and photosynthetic characteristics of these organs at different growth stages of Trapa quadrispinosa Roxb. Results showed that: (1) Submerged leaves exhibited a simpler structure compared to the bifacial anatomy of floating leaves; (2) Adventitious roots at both the juvenile and mature stages retained typical root structures and evident chloroplasts; (3) Significant differences were observed in chloroplast size and morphology among submerged leaves, floating leaves, and adventitious roots; (4) Floating leaves contained significantly higher levels of chlorophyll a (Chla), carotenoid (Car), and total chlorophyll (Chls) compared to other organs, while juvenile adventitious roots and floating leaves exhibited higher chlorophyll b content (Chlb); (5) Floating leaves demonstrated superior photosynthetic efficiency, with higher maximum photochemical quantum yield (F_v/F_m), actual photochemical quantum yield (Y_Ⅱ), and photochemical quenching (qP) compared to the other organs. (6) Based on oxygen exchange rates, the order of the four photosynthetic organs from high to low was juvenile adventitious roots>submerged leaves>floating leaves>mature adventitious roots. Overall, during the seedling stage, photosynthetic capacity was higher in adventitious roots than in submerged leaves. In contrast, during the adult stage, floating leaves surpassed adventitious roots in photosynthetic capacity.