A. del Pozo

The espinal: agroforestry systems of the mediterranean-type climate region of Chile. State of the art and prospects for improvement.

The Central Valley of Chile is largely occupied by a pseudo-savanna called ‘espinal’ consisting of a single dominant tree species, Acacia caven (Mol.) Mol. (Leguminosae), and some 215 annuals, most of which were inadvertently introduced from the Mediterranean Basin. The probable origin and current distribution of the ‘espino’ (Acacia caven) and the espinales in Chile are described. Predominant production systems of the espinal in both the semiarid and subhumid regions of Chile are outlined, with emphasis on the later region. Causes of the current low levels of productivity are discussed, and various strategies for long-term improvement of the espinal are presented.

Acclimation of Photosynthesis and Stomatal Conductance to Elevated CO2 in Canopy Leaves of Wheat at Two Nitrogen Supplies

The great majority of the studies on photosynthetic acclimation have focused on upper-sunlit leaves and little attention has been paid to the acclimatory responses of lower-shaded canopy leaves. In this study we assessed the acclimatory responses of photosynthesis and stomatal conductance (gs), as well as chlorophyll content (Chl) and ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco) activity in flag and lower canopy leaves of wheat growing in polyethylene tunnels set at ambient (360μ mol mol-1) and elevated (700μmol mol-1) CO2 , and under two levels of N supply. The rate of photosynthesis, gs, transpiration (E), Chl and Rubisco activity of sunlit upper- (flag) and shaded lower-canopy leaves were significantly (P<0.05) lower in elevated relative to ambient CO2 -grown plants. All the parameters were lower in N deficient plants, except gs, and all declined with leaf position at both growth CO2 . The acclimatory responses of An and gs to elevated CO2 , evaluated as the ratio of An (or gs) measured at 700μmol mol-1 of elevated to ambient CO2 -grown plants, were enhanced in N deficient plants; with N supply the acclimatory responses were less pronounced in lower canopy leaves relative to flag leaf. It is concluded that in elevated CO2 , photosynthetic capacity and stomatal conductance were reduced in sunlit upper- and shaded lower-canopy leaves, and that N supply reduced acclimation, particularly in lower- canopy, shaded leaves