The ascent of water in tall trees is mainly due to

The ascent of water in tall trees is mainly due to transpiration pull. Transpiration is the process by which water evaporates from the leaves of plants and creates a negative pressure or tension in the water column of the xylem, which is the tissue responsible for transporting water in plants. This negative pressure or tension, combined with the cohesive forces between water molecules, creates a continuous column of water that extends from the roots to the leaves of the tree. The cohesive forces between water molecules allow the water column to remain unbroken, while the transpiration pull provides the force that moves the water up the tree. Adhesive forces between the water and the cell walls of the xylem also help to keep the water column intact and prevent it from breaking under tension. Root pressure, which is the pressure created by the roots of a plant, can also play a role in moving water up a tree, but it is not the main mechanism responsible for water ascent in tall trees.