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Photosynthetic gas exchange, CAM-Cycling, and the ecophysiology of the prostrate-leaved geophyte Brunsvigia orientalis from South Africa

Martin, Craig E., Blocker, Erin
Acta oecologica 2019 v.95 pp. 12-18
Brunsvigia, carbon dioxide, ecophysiology, gas exchange, geophytes, leaves, photosynthesis, soil, temperature, water stress, South Africa
The large leaves of Brunsvigia orientalis and a number of other South African geophytes lie prostrate on the soil, yet potential adaptive benefits of this growth form, as well as the ecophysiology of such plants, remain little studied. Stomatal densities and photosynthetic capacity of the adaxial sides of the leaves of B. orientalis were greater than those of the abaxial sides. Photosynthetic gas exchange at different atmospheric CO2 concentrations was always more limited by the biochemical capacity of photosynthesis of the abaxial side of the leaf, relative to that of the adaxial side. Effects of different temperatures and light levels on photosynthetic gas exchange provided some evidence of adaptation to exposed environments, but interpretation of results was confounded by plant growth conditions. Drought stress substantially reduced photosynthetic rates, although via different mechanisms for the two sides of the leaf. Such stress also induced CAM-Cycling in these thick, but non-succulent, leaves. The results provide little support for the use of soil-respired CO2 by the lower sides of these prostrate leaves, yet reveal previously unknown adaptations of these plants to their stressful environment.