Abstract

CASTELLANOS-PEREZ, E; DE SOYZA, Ag  and  DONART, Gb. Photosynthesis and water use efficiency of the association between Larrea tridentata (DC) Cov. and Muhlenbergia porteri Scribn. Phyton (B. Aires) [online]. 2008, vol.77, pp.297-320. ISSN 1851-5657.

The study was conducted in the Chihuahuan Desert Rangeland Research Center, 32 km north of Las Cruces, NM, USA. Physiological responses of the shrub Larrea tridentata (DC) Cov. and the perennial grass Muhlenbergia porteri Scribn were determined from the summer 1997 to the winter 1998-99 when they grew together. In the summer 1997 Larrea tridentata competed for water with M. porteri, as shrubs growing alone showed higher integrated photosynthesis than shrubs in competi-tion with M. porteri following a heavy rainfall event. Larrea tridentata had lower water use efficiency (WUE) than M. porteri plants. In the summer 1998 M. porteri had greater pre-dawn xylem water potentials (ψ_L) than L. tridentata when soil water potentials were above -3 MPa. Larrea tridentata showed a higher photosynthetic activity when M. porteri was defoliated than when it remained undefoliated. Muhlenbergia porteri presented a higher WUE. While green in the fall, plants of M. porteri had higher ψ_L and WUE than those of L. tridentata. Net assimilation was similar between shrub and grass plants. Both species responded to soil moisture availability in this season. Muhlenbergia porteri had higher net assimilation when growing alone than when growing under creosotebush. In the winter season, and while being small, creosotebush had higher photosynthetic activity when growing alone than when growing with M. porteri (p<0.005). Small and large plants of L. tridentata growing alone showed higher photosynthetic activity than L. tridentata growing with M. porteri (p<0.01). In the spring, M. porteri and L. tridentata had the same net assimilation. At this time, however, water loss was lower in M. porteri than in L. tridentata. When soil water potential decreased below -7 MPa, L. tridentata still showed net assimilation.

Keywords : Larrea tridentata; Muhlenbergia porteri; Photosynthesis.

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