Effects of shading on gas exchange,specific leaf weight and chlorophyll content in four kiwifruit cultivars under field conditions

Diurnal changes of incident photosynthetic photon flux density (PPFD), transpiration rate (E), photosynthetic rate (Pn), stomatal conductance (Cs) and water use efficiency (WUE), together with a number of environmental factors, were measured on individual leaves at well exposed and shaded positions within the canopy for four cultivars of kiwifruit (Actinidia sinensis, P.). Pn and E rates were'much lower in the shaded leaves for all cultivars due to extremely low PPFD values reaching these leaves. Cs followed a trend similar to that for Pn. Exposed leaves showed a significantly higher WUE in the morning, while no difference was observed between exposed and shaded leaves around midday. Specific leaf weight (SLW) was lower in shaded leaves, which had a greater chlorophyll content than exposed leaves.