Plant–Water Relations in Native Shrubs and Trees, Northeastern Mexico

Since plant internal water potentials (Ψ) are a consequence of the soil–plant atmospheric continuum, measuring the actual internal plant water potential and soil water status directly in the field gives us reliable information about the water stress plants may suffer. Hence, it is important to measure water potential to identify the plant’s capacity and strategy to cope with drought. According to the above mentioned, this chapter deals with the physiological adaptation of native trees and shrubs to drought stress in the semiarid ecosystems of northeastern Mexico. The present study has the objective to relate the soil water content with xylem water potential in native woody species such as Condalia hookeri (Rhamnaceae), Cordia boissieri (Boraginaceae), Prosopis laevigata (Fabaceae), and Celtis pallida. Seasonal xylem predawn (06:00 hrs) and midday (12:00 hrs) water potentials were determined at 15 day-intervals. Maximum and minimum seasonal predawn values ranged from −0.67 MPa (C. pallida) to −2.92 MPa (C. hookeri). At midday, xylem water potential varied from −1.07 MPa (C. pallida) to −3.10 MPa (C. hookeri). Predawn water potential values were highly and positively correlated with midday ones (r values varied from 0.900 in C. boissieri, to 0.867 in C. pallida) and rainfall (r 120values ranged from 0.894 in C. hookeri, to 0.697 in C. pallida). Correlation analysis between soil water content at different soil layers with predawn water potential values was weak. During the study, native plant species faced mild to severe drought periods, being the species P. laevigata and C. pallida the ones that achieved higher predawn and midday water potential values. Thus, these species could be considered as drought-tolerant species while C. hookeri and C. boissieri showed lower water potentials and could be in a physiological disadvantage under soil water stress. In conclusion, the study shows that the ability of species to control its water status may depend on the response capacity to absorb water and to control the loss of water during the day.