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

Abstract

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.

What We Know and What We Do Not Know about Dragon Trees?

“…Sap flow thus reflects rates of internal storage use and refilling, both of which are dependent on current and previous transpiration rates-driven by atmosphere and soil moisture. For example, sap flow might sharply increase, even at night under low evaporative demands when the dry soil has been watered (unpublished data) or after intensive rain events following drought [124]. In this case, high night sap flow rates reflect the fast refilling of internal storage desiccated by drought, and do not designate high transpiration.…”

“…In this case, high night sap flow rates reflect the fast refilling of internal storage desiccated by drought, and do not designate high transpiration. For adult trees, the position of the sensor installation is crucial, as it manipulates the percentage of internal storage included in transpiration, which is first used presumably from internal reserves [124].…”

First Age-Estimation Model for Dracaena ombet and Dracaena draco subsp. caboverdeana

“…Fog and clouds bring available water for the long periods of the monsoon that last a few months, while rainfall usually only arrives in a few events during the year. Dragon trees are notably well-adapted for the purpose of mist and drizzle collection from fog and clouds by having long ensiform leaves arranged in leaf rosettes [15,57,58] and the ability of direct water absorption by the leaves [59][60][61]. Thus, the growth speed of dragon trees strongly depends on the altitude as well as the fog and clouds' occurrence.…”

Sap Flow Dynamics and Responses to Grazing and Seasonal Changes in Soil Moisture for Acacia Ancistroclada and Comberatum Molle in a Kenyan Savanna

“…The results demonstrate that SFD within our plots is driven by VPD and air temperature. VPD and air temperature are known drivers of sap ow and transpiration attributable to the water potential gradient, and the ability of dry air to pull water from a source of higher water potential (Nadezhdina et al, 2019). Moreover, the correlation with VPD infers that SFD was coupled with the atmosphere with relatively low boundary layer resistance (Gomenez et al, 2019).…”