Seasonal water relations in four co-existing native shrub species from Northeastern Mexico

摘要

Seasonal xylem water potentials (psi, MPa) and their relationship to soil water content and evaporative demand components were studied in the shrub species Acacia amentacea, Celtis ehrenbergiana, Forestiera angustifolia, and Parkinsonia texana var. macra. Predawn (psi pd) and midday (psi md) water potentials were estimated at 15 days intervals, between January 15 and October 30, 2009 using a Scholander pressure bomb at 06: 00 h (predawn) and 14: 00 h (midday), respectively. During the humid period, psi pd ranged from 0.30 MPa (C. ehrenbergiana), to -0.90 MPa (P. texana). In contrast, over the driest period, psi pd varied between -2.18 (P. texana) and -3.94 MPa (F. angustifolia). At midday, P. texana and F. angustifolia showed the highest (-1.14 MPa) and lowest (-3.38 MPa) psi values, respectively. Average soil water content accounted for 35 to 70% of the variation in predawn psi. Furthermore, both psi reflected the environmental conditions, as indicated by typical correlations observed. The studied shrub species exhibited what seem to be different strategies to avoid damage caused by drought. Thus, P. texana behaved rather as an isohydric plant able to deal well with severe, but short periods of drought. Under exceptionally dry environmental conditions, psi pd undercut psi md values. Similar observations have been made by researchers studying plants in dry ecosystems. All studied native species are recommended for reforestation of the Tamaulipan shrublands, although C. ehrenbergiana and F. angustifolia seem to have limited tolerances for extreme water stress.