A comparative structural and functional study of leaf traits and sap flow in Dracaena cinnabari and Dracaena draco seedlings

Abstract

Water relations for two remote populations of Dracaena tree species from the dragon tree group, Dracaena cinnabari Balfour f. and Dracaena draco (L.) L., were studied to test our hypothesis that morphological and anatomical differences in leaf structure may lead to varied functional responses to changing environmental conditions. Sap flow measurements were performed using the heat field deformation method for four Dracaena seedlings grown in one glasshouse and two greenhouses, and leaf traits related to plant–water relationships were characterised. All traits studied confirmed that D. cinnabari leaves are more xeric in their morpho-anatomical structure compared with D. draco leaves. No radial sap flow variability was detected in D. draco plant stems, whereas sap flow was found to be higher in the inner part of D. cinnabari stems. The regular occurrence of reverse sap flow at night in both Dracaena species was consistent with a staining experiment. Vapour pressure deficit (VPD) was found to be the main driver for transpiration for both Dracaena species. However, the relationship between VPD and sap flow appeared to be different for each species, with a clockwise or no hysteresis loop for D. draco and a counter-clockwise hysteresis loop for D. cinnabari. This resulted in a shorter transpiration cycle in D. cinnabari. The observed superior water-saving strategy of D. cinnabari corresponds to its more xeric morpho-anatomical leaf structure compared with D. draco.

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

“…The drought resistance of these species could also be very high, despite the more mesomorphic appearance, as a recent study on young transplants of mesophytic D. marginata confirmed [86]. The xeromorphic species have more deeply sunken stomata (D. ombet, D. serrulata, and D. cinnabari) (Figure 3c), which are distributed irregularly or parallel to the leaf axis regularly over the entire area [13,43,84]. Sunken stomata are mostly surrounded by cuticular thickenings forming a rim, which appears square, oval, or rectangular in outline [43].…”

“…The leaf microstructure of Dracaena species ranges from mesomorphic to xeromorphic. Mesomorphic traits are the slightly bulging stomata, or stomata that are located at the level of other epidermal cells (e.g., D. draco, D. kaweesakii) [43,84] (Figure 3d), although slightly sunken stomata could also be observed (e.g., D. jayniana) [43]. Such stomata are more or less distributed in rows (D. draco, D. tamaranae, D. jayniana) [43,84], but the entirely scattered stomata were also observed (D. kaweesakii) [43].…”

“…The cuticle of more mesomorphic species is thinner, ranging approx. from 1 to 13 µm and fiber bundles are mostly hypodermal [43,84,85] (Figure 3b). The drought resistance of these species could also be very high, despite the more mesomorphic appearance, as a recent study on young transplants of mesophytic D. marginata confirmed [86].…”

Local Management System of Dragon’s Blood Tree (Dracaena cinnabari Balf. f.) Resin in Firmihin Forest, Socotra Island, Yemen

“…Additionally, a study published by Maděra et al [9] estimated that the mortality was less than 1%, which differed substantially with the age of the trees. Despite the long-term morphological, anatomical, and physiological adaptations of the DC trees to arid climate conditions [22,[28][29][30]32,55], the present tree populations do have an evidently unbalanced age structure with a largely disorganized woodland structure and a lack of natural regeneration [16].…”

Comparative leaf micromorphology and anatomy of the dragon tree group of Dracaena (Asparagaceae) and their taxonomic implications

“…Preliminary studies of leaf anatomical structure in D. cinnabari and D. draco were presented by Petroncini et al (2003) and Nadezhdina et al (2015).…”