Final answer:
The matric potential (Ym) is the aspect of water potential in plants that cannot be manipulated by the plant, as it depends on the interaction between water and the plant materials.
Step-by-step explanation:
The component of the total water potential that cannot be manipulated by the plant is the matric potential (Ym). Matric potential represents the interaction between water and hydrophilic molecules lining the vessels and tracheids. While plants can adjust osmotic potential (Ys) through solute concentration, pressure potential (Yp) through turgor pressure, and gravitational potential (Yg) naturally varies with height, the matric potential is solely due to the physical properties of the water and the plant material absorbing water.
Water potential in plants is a crucial concept, as water moves from an area of higher water potential to an area of lower water potential. This movement is essential for the processes of transpiration and the transport of nutrients and water up through the plant's xylem. Hence, although plants have mechanisms to regulate other aspects of water potential, the matric potential component is out of their control, making it a fundamental factor in the overall water potential equation.