ABSTRACT
Chlorine (from the Greek “chloros” meaning yellowish green, which describes the color of the gaseous diatomic molecule it exists as under standard conditions) is a member of the halogen family and is a strong oxidizing agent. Chlorine combines with elements to create chlorides (Winterton, 2000). Chlorine exists predominantly in soils and plants as chloride, one of the most common anions in nature. This anionic form contributes greatly to the behavior of chlorine in the environment and its function in plants (Winterton, 2000). Although plants can take up chloride in amounts of 50-500 μmol ⋅ kg−1, which is similar to macronutrient accumulation, the requirement of chloride for plant growth is considerably lower, clearly establishing it as a micronutrient (Mengel and Kirkby, 1987). Chlorine deciency in plants seldom is observed in agriculture or nature due to the plentiful supplies of chlorine in the environment and its redistribution from natural occurrences such as
9.1 Historical Background .......................................................................................................... 347 9.2 Uptake of Chlorine by Plants ...............................................................................................348 9.3 Physiological Responses of Plants to Supply of Chlorine .................................................... 349
9.3.1 Role in Photosynthesis .............................................................................................. 349 9.3.2 Role in Stomatal Regulation ..................................................................................... 350 9.3.3 Role in Vacuolar Transport ....................................................................................... 350 9.3.4 Osmotic Adjustment in Halophytes .......................................................................... 351 9.3.5 Activation of Enzymes .............................................................................................. 351 9.3.6 Other Functions of Chloride in Plants ...................................................................... 352
9.4 Genetics of Acquisition of Chlorine by Plants ..................................................................... 352 9.5 Concentrations of Chlorine in Plants and Plant Parts .......................................................... 353 9.6 Ratios of Chlorine and Interactions with Other Elements .................................................... 355 9.7 Diagnosis of Chlorine Status in Plants ................................................................................. 356
9.7.1 Decient Conditions ................................................................................................. 357 9.7.2 Excessive Conditions ................................................................................................ 357
9.8 Forms and Concentrations of Chlorine in Soils and Availability to Plants .......................... 358 9.8.1 Forms and Concentrations of Chlorine in Soil ......................................................... 358 9.8.2 Factors Affecting Chlorine Availability to Plants .................................................... 359
9.9 Assessment of Chlorine Status in Soils ................................................................................ 359 9.9.1 Extraction of Chloride from Soils ............................................................................ 359 9.9.2 Determination of Chloride in Soil Extracts ..............................................................360
