Drought response strategies for deciduous species in the semiarid Caatinga derived from the interdependence of anatomical, phenological and bio-hydraulic attributes

Abstract

Deciduous species from semiarid environments have different strategies for overcoming seasonal drought. However, these strategies are little explored for semiarid regions, particularly due to the lack of studies that integrate morpho-physiological mechanisms, including the vulnerability of the hydraulic system. In this work, we seek to integratively analyze the physiological, anatomical, hydraulic, phenological and wood density aspects of four deciduous species, representing opposite functional groups: (1) high wood density (HWD), (2) low wood density (LWD), from the Caatinga, a Brazilian semiarid region. The analyses covered leaf phenology, stomatal conductance, water potential, and chlorophyll content, as well as the anatomy and hydraulic architecture of branches and leaves. As predicted, the interrelationship between anatomy, physiology, and phenology was crucial to enhance the understanding of drought resistance strategies. LWD species tend to avoid drought, while HWD species tend to be more tolerant to it. LWD species showed an anticipated leaf fall to the dry season, in addition to a potential hydraulic conductivity 66.8% higher than HWD species, as well as a higher stomatal density (24.8%). However, LWD species were approximately 50% potentially more vulnerable than HWD species. The leaves of HWD species had gelatinous fibers surrounding the central rib, indicating traits of mechanical tolerance to dehydration. On the other hand, LWD species use preventive strategies to keep their water potential high during the dry period. These results highlight the importance of hydraulic architecture in the interrelationship of biological factors that determine the plant's drought stress performance as a function of the functional group.