Long-term in situ sap flow monitoring in a mature Dracaena cinnabari tree on Socotra

Dracaena cinnabari is a relict of the remote Socotra Island (Yemen) where it grows at higher altitudes with the frequent occurrence of fogs. D. cinnabari as the only representative of the dragon tree group creates woodlands and forests on the Socotra Island. It is not clear what mechanisms allow this relict arborescent monocot to survive harsh climate and poor soil of karst rocks there. In this work, we conducted long-term sap flow monitoring in the stem and roots of the mature D. cinnabari plant during the driest period of year between two regular monsoons. We aimed to reveal plant responses to a range of environmental conditions and to understand mechanisms of drought survival by this woody monocot. Several following features of sap flow performance were found: high flow sectoriality in the stem and in roots corresponding to the intensity of insolation, free lateral flow, higher stem integrity compared to roots, internal storage replenishment from the fog followed by increased transpiration presumably from the refilled stem storage. Results indicate that in studying the sap flow dynamics in the mature D. cinnabari tree, plant water storage should be included in the analyses in addition to soil water availability and intensity of evaporating demands. The ability to replenish succulent woody organs from atmospheric water and to survive long periods of drought from the internal supply distinguishes the behavior of this short-rooted arborescent monocot from the known strategies of deep-rooted trees in arid areas.