The influence of short-term partial shading on photosynthesis and stomatal conductance in relations to cropload and water status of grapevines and apples
1998
Nabi, Ghulam
Short-term shading of part of the canopy was studied in grapevines (Vitis vinifera L.) cv. Pinot noir and apples (Malus pumila) MM106 cv. Gala. In most experiments shading caused a rapid increase in the net photosynthesis (A) and stomatal conductance (gs) of the illuminated part of the canopy. The fully expanded new leaves appeared to be most sensitive to shading in both crops and A and gs increased by 55 and 20% respectively, for grapevines within 30 minutes. This response was reversed when the shading was removed. Fruiting grapevines had a higher A and gs (4.7µmol CO₂ m⁻²s⁻¹ and 0.08 mol H₂O m⁻²s⁻¹, respectively), than non-fruiting vines (2.9 µmol CO₂ m⁻²s⁻¹ and 0.05 mol H₂O m⁻²s⁻¹, respectively), and water-stress reduced A and gs compared to well-watered vines. Intercellular CO₂ concentration (Cᵢ) was unaffected by shading or crop loading. The overall response by vine S to partial shading was similar across all water stress and crop loading treatments. It is concluded that in grapevines and apples, the rapid changes in A and gs in the illuminated part of the canopy caused by partial shading elsewhere, are regulated by hydraulic processes. However, the mechanisms by which stomata sense those changes are still unknown.
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