Interplay between stomatal regulation capacity, hydraulic traits and growth performance in three shrub species in a tropical montane scrubland under contrasting water availability

Abstract:

The maintenance of water transport is of utmost ecological importance to plants, this process is essential to plant carbon assimilation and growth. Plants can adjust their water use and hydraulic safety through the coordinated regulation of hydraulic and stomatal conductivity, in which, plants can vary from an isohydric to an anisohydric behavior. Isohydric species adjust their stomatal opening and maintain water potential relatively stable as water availability changes. Anisohydric species do the opposite pattern. In this study, we investigate how stomatal regulation capacity is associated to hydraulic traits (xylem water potential in which plants lose 50% (P₅₀) and 88% (P₈₈) of their hydraulic conductivity), root depth, and growth in three shrub species under contrasting water availability. We implemented a throughfall exclusion experiment to simulate drier conditions in the biodiverse mountain-top scrublands (the campos rupestres) in Brazil and evaluated the performance of three species: Campomanesia pubecens (Myrtaceae), Eremanthus seidellii and, Lessingianthus warmingianus (Asteraceae). These species showed different hydraulic strategies: C. pubecens showed an anisohydric strategy, while E. seidellii and L. warmingianus exhibited an isohydric strategy. E. seidellii is a deep-rooted species and the other two species showed shallow roots. E. seidellii showed the xylem more vulnerable to cavitation. Our drought treatment reduced the growth only in L. warmingianus. This species showed a brevideciduous phenology, decreasing its leaf area during the dry season and flushing new leaves in the end of the dry season. The xylem more resistant to cavitation in this species might help the species to flush new leaves before the onset of the wet season. The other two evergreen species with contrasting hydraulic strategies species display a trade-off between root depth and vulnerability to cavitation. The isohydric species was more vulnerable to cavitation, but to compensate exhibits the deepest root system. C. pubecens does the opposite. Our results illustrate the diversity of strategies that plants might present to deal with drought, showing different trade-offs to maintain the plant functioning in drought conditions.