干旱区生态环境知识资源中心

Stem CAM with a peripheral chlorenchyma in stem succulents growing up to arborescent sizes and life forms appears to be a unique evolution as it requires delayed and reduced bark formation and stem stomata. However, stem succulence as a convergent morphotype and with it the stem CAM physiotype evolved polyphyletically in many divergent taxa of the dicotyledonous angiosperms. Controlling water budgets is the main ecophysiological benefit of stem succulence and CAM, where the cooperation of a peripheral photosysnthetically active chlorenchyma and a central water storing hydrenchyma is co-ordinately regulated. Thus, a major factor important for performance of stem CAM succulents at the community level is water or drought. Although this implies fitness under osmotic stress, CAM performing stem succulents are not adapted to salinity and are salt stress avoiders where they occur in saline habitats. Notwithstanding the low overall productivity of CAM plants in general, stem CAM plants can show very high productivity under certain circumstances and may also respond to elevated environmental atmospheric CO2 concentrations with increased growth.