What contributes most to the transport of water from soil to the leaves of a tall tree?
The cohesion of water and transpiration pull contributes most to the transport of water, from the ground to the leaves of a tall tree. It is the phenomenon of attraction between similar molecules. The strong cohesive force maintains a continuous channel for water.
The transpirational pull is the pulling force responsible for lifting the water column. As water is lost in form of water vapour to the atmosphere from the mesophyll cells by transpiration, a negative hydrostatic pressure is created in the mesophyll cells which in turn draw water from veins of the leaves.
Thus, the transpiration pull acts as pull from above on-the-whole of the water column of the plant which pushes the water column of xylem vessels of roots towards leaves i.e., in an upward direction.