Contribution of corticular photosynthesis to bud development in African baobab (Adansonia digitata L.) and Castor bean (Ricinus communis L.) seedlings

• A light-exclusion study was done to find out the contribution of stem to carbon gain.
• Light exclusion resulted to an increase in height and stem diameter during drought.
• Light exclusion resulted in a significantly lower bud DW production.
• Light exclusion resulted in an enrichment in bud and stem 13C composition.
• Corticular photosynthesis contributed to carbon gain in two stem succulent plants.

The African baobab (Adansonia digitata L.) and castor bean (Ricinus communis L.) are drought resistant green-stemmed succulent plants which grow in the arid and semi-arid regions of Africa. Photosynthesis in the stems of green-stemmed plants is known to contribute to plant carbon gain especially during leafless periods. To study the contribution of stem photosynthesis in stem succulent plants, the height and stem diameter of baobab and castor bean plants grown in the greenhouse were measured. The plants were completely defoliated and subjected to different treatments: Watered with open stems (WO), watered and stems covered with aluminium foil (WC) to achieve 100% light exclusion, drought and open (DO) and drought and covered (DC). Stem coverage with aluminium foil resulted in a higher stem height and diameter during drought for baobab with similar trends seen in castor bean. Light exclusion resulted in a significantly lower bud DW production and enrichment in 13C in bud dry matter of castor bean and in stem dry matter of baobab. These show that corticular photosynthesis contributes in carbon gain in these species.