Photosynthetic Acclimation of Sweet Pepper Plants to Screenhouse Conditions
Leaf gas exchange and photosynthetic light acclimation of sweet pepper leaves were investigated in a Mediterranean area (central Greece) in the open field and in three screenhouse nets differing in color, shading intensity (Si), and porosity from May to Oct. 2011. The screenhouse nets were two insect-proof white nets (W13 and W34, SI = 13% and 34%, respectively) and a green shading net (G36, SI = 36%). Leaf net CO2 assimilation (A(n)), transpiration rate (E), and stomatal conductance (g(S)) were measured by means of a portable gas exchange device on leaves located in three canopy layers. The differences in light regime within the canopy induced by the three shading nets had only a slight effect on A(n), thereby resulting in substantially higher light-use efficiency under shading than in the open field. The observed tendency toward higher gs in shaded plants was counterweighted by a lower intercellular-to-ambient CO2 concentration gradient, leading to similar A(n) in leaves of shaded and non-shaded plants. Ontogenic effects (leaf aging) appeared to be the main factor determining the decreasing seasonal trend of leaf photosynthetic attributes. Overall, shaded sweet pepper plants display a physiological light acclimation allowing them to maintain the photosynthetic activity to a level similar to that observed in non-shaded plants across a wide range of growth light regimes, irrespective of the type of net and its shading intensity.