Coordination of rooting depth and leaf hydraulic traits defines drought-related strategies in the campos rupestres, a tropical montane biodiversity hotspot

Abstract

The survival and coexistence of plants in water-limited environments are related to their ability to coordinate water acquisition and regulation of water loss. To assess the coordination among below and aboveground hydraulic traits and the diversity of water-use strategies, we evaluated rooting depth and several leaf hydraulic traits of 15 species in campos rupestres, a seasonally-dry biodiversity hotspot in central Brazil. We assessed the depth of plant water acquisition by excavating roots and analyzing the stable isotope composition of hydrogen (δD) and oxygen (δ18O) in the xylem and soil water. We also measured mid-morning stomatal conductance, leaf-water potential at turgor loss point (ѰTLP) and pre-dawn leaf water potentials (ѰPD) during wet and dry seasons. We demonstrated that rooting depth is a good predictor of seasonal variations in stomatal conductance and ѰPD. Shallow-rooted plants had greater variation in stomatal conductance and ѰPD than deep-rooted plants. Woody plants with shallower roots also had lower ѰTLP than deep-rooted plants, revealing higher drought resistance. We demonstrate that shallow-rooted species, more exposed to variation in water availability, have mechanisms to confer drought resistance through turgor maintenance. Our results support the theory of hydrological niche segregation and its underlying trade-offs related to drought resistance.