Adaptations to Drought in Five Woody Species Co-Occurring on Shallow-Soil Ridges

Abstract

Pre-dawn leaf water potential and parameters controlling water flow through a plant of five co-occurring plant species, Dodonaea viscosa Jacquin (Sapindaceae), Wikstroemia pseudoretusa Koidzumi (Thymelaeaceae), Ligustrum micranthum Zucc. (Oleaceae), Distylium lepidotum Nakai (Hamamelidaceae) and Hibiscus glaber Matsumura (Malvaceae) were compared in late April, early June and early September 1989. These species are common members of the scrub community found on shallow-soil ridges in the Bonin Islands, Japan. Mean pre-dawn leaf water potential during the dry period of early September was lowest in Dod. Viscosa growing on microsites with shallower soil on a ridge. Deeper rooted species, Dis. Lepidotum and H. glaber, had higher values of pre-dawn leaf water potential than shallower rooted species, L. micranthum and W. pseudoretusa. Anatomical and morphological characteristics, and physiological characteristics such as water relations of leaves suggested that W. pseudoretusa and H. glaber are less tolerant to drought than L. micranthum and Dis. Lepidotum, and that W. pseudoretusa and H. glaber might avoid severe stress by temporal leaf fall and dense deeper root, respectively. Relationships between leaf conductance and hydraulic conductance suggested different water use patterns among the five species growing in close proximity on xeric shallow-soil ridges in the Bonin Islands.