Lonicera confusa has an anatomical mechanism to respond to calcium-rich environment

Calcium (Ca) is an important nutrient element for plant growth and development. Nevertheless, excessive Ca restricts plant communities in Ca-rich environments. Lonicera confusa DC. is one species adapted to Ca-rich environments in the karst area of southwest China; however, the anatomical mechanism that allows these plants to respond to a Ca-rich environment remains unclear. L. confusa was cultivated in two types of soil with controlled Ca levels. The ultrastructure of leaves at different developmental stages was observed, and their Ca contents analyzed by laser scanning confocal microscope and energy-dispersive X-ray spectroscopy. There was no significant difference in leaves between the two experimental groups at very early stages of development. The glands of leaves growing in Ca-rich soil became saturated and showed a steady increase of Ca content in the following stages. The Ca level in leaf trichomes also increased steadily, compared with those from Ca-poor soil. When the leaves matured, Ca salts were excreted via stomata of L. confusa from Ca-rich soil. L. confusa had a special anatomical mechanism of responding to Ca-rich environments by excreting Ca salts via stomata, and storing Ca2+ in leaf glands and trichomes.