ABSTRACT
Sulfur (S) has been recognized as a plant nutrient since the time of Liebig, who indicated that S was accessed by plants from the soil solution (Meidner, 1985). Sachs also determined that S was an essential element from his own and previous research (Sachs, 1865; cited by Epstein, 2000). In the past, deciencies were relatively rare in industrialized areas due to inadvertent inputs of S from industrial pollution (Lehmann et al., 2008) and in the superphosphate and ammonium sulfate fertilizers that were used frequently to supply P and N. In regions with limited industrialization and low atmospheric input of S, such as the Northern Great Plains of North America, S deciencies were recognized early. For example, S deciencies were identied in the Canadian prairies as a risk for legume production in the 1930s and for canola (rapeseed, Brassica napus L.) in the late 1960s and early 1970s (Hamm, 1967; Hamm et al., 1973; Beaton and Soper, 1986). In the Prairie Provinces, there are more than 4 million ha of agricultural soils decient in plant-available S and substantially greater areas are potentially decient (Bettany and Janzen, 1984; Doyle and Cowell, 1993). With movement to intensive crop
7.1 Historical Background .......................................................................................................... 261 7.2 Uptake of Sulfur by Plants ................................................................................................... 262 7.3 Physiological Responses of Plants to Supply of Sulfur ........................................................ 263
7.3.1 Forms of Sulfur in Tissue ......................................................................................... 263 7.3.2 Transport of Reduced Sulfur ....................................................................................264 7.3.3 Oxidation-Reduction and Detoxication Functions ................................................264 7.3.4 Functions of Secondary Sulfur Compounds.............................................................265 7.3.5 Response of Plants to Sulfur Deciency ..................................................................266 7.3.6 Symptoms of Sulfur Deciency ................................................................................ 267
7.4 Molecular Genetics of Sulfur Acquisition by Plants ............................................................ 271 7.5 Concentrations of Sulfur in Plants ........................................................................................ 274 7.6 Ratios and Interactions of Sulfur with Other Elements ........................................................ 275
7.6.1 Nitrogen .................................................................................................................... 275 7.6.2 Phosphorus ................................................................................................................ 277 7.6.3 Micronutrients .......................................................................................................... 278
7.7 Diagnosis of Plant Sulfur Status ........................................................................................... 279 7.8 Forms and Concentrations of Sulfur in Soils and Availability to Plants .............................. 281
7.8.1 Organic Sulfur Pools ................................................................................................ 281 7.8.2 Inorganic Sulfur ........................................................................................................284
