THE EFFECTS OF WATER STRESS ON PLANT GROWTH

INTRODUCTION

Water is the matrix of life. Many cellular activities and physiological processes within a plant depend on water as a solvent. Indeed, a cell's enlargement could not take place without the influx of water stretching it's wall. Consequently, plant "growth" would not be possible!

Water deficiency may result from a number of causes including lack of soil water, excessive transpiration, high soil water salt content, damaged roots, and poor soil quality. While the presence of water may be evident in the soil, it may typically be other than optimal. For this reason, reduction in growth commonly remains unnoticed. Visual water stress symptoms usually start with wilting of leaves, and beyond this chlorosis, leaf drop, shoot tip die-back, and necrosis may result. The degree too which a plant is adversely affected by water deficit may depend on a number of factors including genetic adaptation, dehydration tolerance (low water potential in cells), and avoidance mechanisms (thick cuticles, deep rooting, etc.).

Excessive soil water may also lead to negative effects on plant growth. As water levels increase, more oxygen is displaced from soil pore space, and respiration is inhibited. As root cells are unable to engage in this basic life process, they begin to rot and eventually die. Unable to absorb soil water, above ground plant parts begin to show the symptoms of water stress--reduced vigor, chlorosis, and in the worst instance, death.

Flooding, over irrigation, excessive rainfall, poor soil drainage, perched water tables, and hardpans can all create water excess. Symptoms are often similar or identical to those of water deficit, and again, sensitivity varies with the species.

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