Question

how root pressure helps in movement of water in plants at nights​

Answer 1

Evaporation of water molecules from the cells of a leaf create a suction which pulls water from the xylem cells of roots. The loss of water from the aerial parts of the plant is known as transpiration

Thus, transpiration helps in the absorption and the upward movement of water and minerals dissolved in it from roots to the leaves. The effect of root pressure is more important at night. During the day when the stomata are open, transpiration pull becomes the major driving force in the movement of water in xylem .