How does matric potential affect plant-available water?
• Explain why plants cannot absorb water at the wilting point. Plants withdraw water from soil pores, working against capillary forces that hold water in the soil. Plant-available water 1 is the amount of water in a soil between field capacity 2 and the wilting point 2. Plants have increasing difficulty withdrawing water as the water content decreases. This level of difficulty is simply a measure of the work needed to overcome capillary forces 4, expressed as the matric potential 2. Eventually, the forces pulling water into plant roots cannot overcome the capillary forces holding water in soil pores and the plant wilts for lack of sufficient water.
