Crop yield response to water - Cra

ox 2 Understanding the transpiration process.Water loss from plant leaves takes place primarily through pores called stomata thatare opened during daylight hours and close at night. Stomata are also the path forthe entrance of carbon dioxide into the leaves, the necessary input for photosynthesis.Transpiration losses from leaves trigger a sequence of events in the soil tree system;water moves from the shoots into the leaves to compensate for leaf losses, drawingwater from the trunk into the shoots; this in turn, draws water from the roots to thetrunk, and finally, from the soil to the roots. Thus, liquid water flows from the soilto the sites in the leaves where it evaporates before diffusing through the stomatato the atmosphere. Water moves passively through this path following a gradientin potential energy, from the soil to the leaves. In any location along this path, suchenergy level may be determined and is called water potential. Furthermore, the waterflow encounters resistance all along the pathway from the soil to the atmosphere (seediagram). The tree exerts some control on this water flow, which is needed to matchthe transpirational loss to the evaporative demand of the environment. When there areimbalances between supply and demand, the tree controls its water loss through theadjustment of the degree of stomatal opening and by other means.The water flow from soil through tree to the atmosphere.Yield Response to Water of Fruit Trees and Vines 255