Leaf phenology and water potential of five arboreal species in gallery and montane forests in the Chapada Diamantina; Bahia; Brazil

The influence of water potential (ΨW) on the leaf phenological behaviors of five arboreal species within gallery and montane forests on the eastern slope of the Chapada Diamantina Mountain Range in Bahia State, NE Brazil, was examined to investigate the following questions: (1) Do seasonal variations in rainfall influence the water potential of these species in their natural habitats (gallery and montane forests)? (2) Do the gallery forest species show smaller daily variations in their water potential and greater nocturnal recuperation than montane species? (3) Can the water potentials of these species be used to identify their particular types of leaf phenologies? The species examined were Tibouchina fissinervia and Clusia nemorosa (evergreen with continual leafdrop); Tapirira guianensis and Vochysia pyramidalis (evergreen with concentrated leafdrop), and Maprounea guianensis (brevi-deciduous) were chosen based on their abundance, importance value indices, and contrasting phenological behaviors. The leaf phenologies of all species were similar in both forest types. Evergreen species with continual leafdrop demonstrated leaf budding and leaf fall occurred at low levels during the entire year. Evergreen species with continual leafdrop as well as brevi-deciduous species demonstrated peaks of leaf fall and leaf budding during the dry period. Brevi-deciduous trees remained without leaves for an average of three days. The major episodes of leaf budding occurred during the dry period in all of the species examined. M. guianensis usually demonstrated low predawn (ΨPD) and midday (ΨMD) water potentials (ΨW). C. nemorosa demonstrated the greatest ΨPD and ΨMD values and the lowest daily amplitude (ΔΨ), suggesting that this plant used CAM during most of the study period. The majority of the species demonstrated small seasonal differences in ΨW, and the ΨPD values indicated a satisfactory nocturnal recuperation of their water status, even during the dry period. The maximum daily amplitude of ΨW was observed in V. pyramidalis, a species dependent on moist habitats for establishment and growth. No large decrease in ΨPD was observed during the study period in the species examined here, and all species demonstrated leaf budding during the dry period, suggesting that there were no severe water restrictions in either the gallery or montane forests. However, during dry periods, the species generally demonstrated lower ΔΨ. This reflects the restriction of transpiration, which according to phenological data, may occur due to different mechanisms, depending on the species. Our data supports the view that there is no strict relationship between decreasing water status in these plants and leaf fall.

Research highlights▶ We feel that this manuscript brings new data to the interphase between ecophysiology and phenology. ▶ Our data does not corroborate integrally with what is currently known about the relationship between water potential and phenology, which suggests that this is an area that will require further investigations. ▶ As such, we believe that new information about this subject that is backed by sound data should be encouraged.