Movement of water through the soil-plant-atmosphere system [articol]

Abstract

The flow of liquid water from the soil into the plant depends on the plant having a lower water potential than the soil; thus the soil water potential determines the availability of soil water for diffusion into the plant. As soils dry, the water potential decreases, making it more difficult for plants to obtain the water they need to grow. Once water enters the plant through its roots, it moves through the plant vascular system to the leaves if the leaves have lower water potentials than the roots. The general flow pattern is: soil → root cells → endodermis → xylem → leaf cells → stomata → air. The water potential in the soil are gravitational, matric, osmotic and overburden. In the plant the water potential are osmotic, matric and turgor. The driving force for the movement of water in the soil and hence also towards the plant roots is constituted by the hydraulic potential gradient. Flow external to the vascular system also results from a hydraulic potential gradient. The amount of water arriving at the total root surface should be equal to the amount transpiring from the leaves, otherwise the plants will wilt. Plant response to the soilmoisture regime depends also on a large number of environmental variables such soil, plant and meteorological factors