Roque Gonzalo Ramírez-Lozano

Xylem water potentials of native shrubs from northeastern Mexico

Abstract Xylem water potentials (Ψ) were evaluated in browse plants such as Forestiera angustifolia (Oleaceae), Celtis pallida (Ulmaceae), Zanthoxylum fagara (Rutaceae), and Eysenhardtia texana (Fabaceae). Collections were carried out at Linares County, a semi-arid region of northeastern Mexico. Ψ (MPa) were estimated at 10-day intervals between July 10 and September 30, 2008 by using a Scholander pressure bomb, and were monitored in five different plants per species at 06:00 h (predawn) and 14:00 h (midday). Air temperature, relative humidity, precipitation, and soil water content were registered throughout. Data were subjected to one-way ANOVA and linear correlation analysis. At the wettest period, Ψ at predawn varied from − 0.29 (C. pallida and E. texana) to − 0.37 (F. angustifolia and Z. fagara); in contrast, at the driest period, predawn Ψ ranged from − 3.28 (F. angustifolia) to − 4.50 (Z. fagara). At midday E. texana achieved the highest (−1.14) and lowest (−4.20) values at wettest and driest sampling dates, respectively. It seems that air temperature and vapor pressure deficit negatively influenced Ψ values in all species; conversely, Ψ values augmented as relative humidity increased. Since F. angustifolia and C. pallida maintained higher predawn and midday Ψ values under water stress, these species may be considered as drought-adapted species while, Z. fagara and E. texana that acquired lower values, may be less adapted to drought and in physiological disadvantage under limited water conditions.

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

ABSTRACT Seasonal xylem water potentials (Ψ, 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 (Ψpd) and midday (Ψmd) 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, Ψpd ranged from −0.30 MPa (C. ehrenbergiana), to −0.90 MPa (P. texana). In contrast, over the driest period, Ψpd 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) Ψ values, respectively. Average soil water content accounted for 35 to 70% of the variation in predawn Ψ. Furthermore, both Ψ 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, Ψpd undercut Ψmd 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.

Nutritional value of Acacia amentacea and Parkinsonia texana grown in semiarid conditions

In order to evaluate the nutritional value of Parkinsonia texana and Acacia amentacea, two leguminosae species of the Tamaulipan scrubland, Northeastern Mexico, two experiments were carried out: the first tested the effects of season and browse species on chemical composition as nutritional variable to small ruminants; the second tested the effect of the addition of polyethylene glycol (PEG) on fermentation parameters. Foliage samples were collected from three sites. Data of chemical composition were analysed using analysis of variance for a bi-factorial arrangement, whereas the effect of PEG was analysed by a strip plot design. Results of chemical composition were affected by interacting factors season*species as individually they were significantly different (P<0.001). Addition of PEG affected (P<0.001) fermentation parameters. Significantly higher values of neutral detergent fibre (42%), condensed tannins (19%), purines (9 μmol), partitioning factor (PF) (6.1) and gross energy losses (GEL=6.7%) were found in A. amentacea, while P. texana gave higher crude protein (18%), in vitro true organic matter digestibility (82%), metabolisable energy (ME) [2.1 Mcal/kg dry matter (DM)], A (183 mL), c (0.07/h) and L (0.86 h). Addition of PEG increased ME, and affected (P<0.001) fermentation parameters A and c, while purines and PF decreased. Results indicate that chemical composition and fermentation parameters vary according to seasons and species. PEG addition increases the fermentation parameters, which indicates that PEG counteracts the detrimental effects of secondary components of samples. Data suggest that using both species combined could supply necessary nutritional requirements to small ruminants in the Tamaulipan scrubland.