Water is pulled up through the xylem as water is lost from the leaves by transpiration. This means that anything that changes the rate of transpiration also changes the rate of water uptake by the plant. Three important factors are light intensity, air movement and temperature.
Light intensity. In bright light the stomata open wider, so more water vapour can diffuse out and the rate of transpiration increases. In the dark most stomata close and transpiration is very slow.
Air movement. Moving air carries water vapour away from the surface of the leaf. This keeps the concentration gradient of water vapour steep, so water vapour diffuses out faster. In still air the water vapour builds up near the leaf and the rate falls. High humidity has a similar effect because the concentration gradient is small.
Temperature. At a higher temperature the water molecules have more kinetic energy. Water evaporates faster from the mesophyll cells and diffuses out faster, so transpiration and water uptake increase.