Final answer:
The water potential equation, influenced by solute concentration, pressure, gravity, and matric potentials, explains how water moves in plant systems. With a pressure potential of zero, the solute potential becomes the significant contributing factor to the system's total water potential. Adding solute can alter water potential and help achieve equilibrium.
Step-by-step explanation:
Water potential (ψ) is crucial in understanding water movement within plant systems. It is the measure of potential energy of water in a system compared to pure water, influenced by several factors such as solute concentration, pressure, gravity, and matrix effects. When the pressure potential (Yp) equals 0, the water potential is determined by the other components of the equation Ysystem = Ytotal = Ys + Yp + Yg + Ym, where Ys is the solute potential, Yg is related to gravity, and Ym is the matric potential. Adding solute to one side of the tube can counterbalance the positive water potential on the other side in an attempt to reach equilibrium since solutes reduce the free energy of water, thus affecting its movement across a membrane or within different parts of a plant.
Solute potential (ψs), or osmotic potential, is specifically calculated using the van 't Hoff equation: Ys = -MiRT, where M is the molar concentration, i is the van 't Hoff factor, R is the ideal gas constant, and T is the temperature in Kelvin. Solute potential is always negative in a solution with dissolved solutes, as solutes bind to water molecules and reduce the amount of free energy available for work, therefore decreasing water potential.