Leaf structure and inorganic carbon acquisition strategies of heteroblastic aquatic plants at different stages of development

Six heteroblastic aquatic plants, i.e., Nymphaea tetragona Georgi, Nuphar pumila (Timm) de Candolle, Nuphar sagittifolia Pursh, Potamogeton distinctus A. Bennett, Potamogeton octandrus Poir, and Alisma plantago-aquatica L., were studied and their chlorophyll content, stomatal traits, anatomical structure, and HCO₃^- utilization were analyzed, the differences between leaf structure and inorganic carbon acquisition strategies at different developmental stages were compared.Results showed that the juvenile leaves were thinner and had fewer cell layers than the mature leaves. The upper and lower surfaces of the juvenile leaves did not contain stomata, whereas the upper epidermis of the mature leaves did contain stomata. Thus, the juvenile leaf structure showed increased cell surface area and the ability to absorb inorganic carbon underwater, while the mature leaves structure better absorbed CO₂ from the atmosphere. Results from pH-drift analysis indicated that the juvenile leaves exhibited better acquisition of underwater inorganic carbon as an adaptation to the submerged environment. In addition, the juvenile leaves of P. distinctus and P. octandrus used HCO₃^- in the water as an additional carbon source, which was beneficial for growth in the submerged environment. These results elucidate the leaf structure of heteroblastic aquatic plants at different stages of development and the adaptability of inorganic carbon acquisition strategies to the submerged and aerial environments.