Role of Sulfur for Plant Production in Agricultural and Natural Ecosystems

Abstract

Sulfur is essential for plant growth and functioning. Sulfate taken up by the roots is the primary sulfur source for growth, but additionally plants are able to utilize absorbed sulfur gases by the shoot. Prior to its assimilation sulfur needs to be reduced and cysteine is the primary precursor or sulfur donor for other plant sulfur metabolites. Sulfur is of great significance for the structure of proteins and functioning of enzymes and it plays an important role in the defense of plants against stresses and pests. Sulfur metabolites such as glutathione provide protection of plants against oxidative stress, heavy metals and xenobiotics. Secondary sulfur compounds (viz. glucosinolates, γ-glutamyl peptides and alliins), phytoalexins, sulfur-rich proteins (thionins), localized deposition of elemental sulfur and the release of volatile sulfur compounds may provide resistance against pathogens and herbivory. Plant species vary largely in sulfur requirement, and an adequate and balanced sulfur nutrition is crucial for their production, quality and health. The assimilation of sulfur and nitrogen are strongly interrelated and sulfur deficiency in plants can be diagnosed by the nitrogen to sulfur ratio of plant tissue. In agricultural ecosystems, the occurrence of sulfur deficiency of soils can easily be corrected by the application of sulfur fertilizers, which additionally prevents negative environmental side effects such as leakage of nitrate to drainage water. Plants in natural ecosystems generally have an adequate sulfur supply, which partly originates from atmospheric sulfur inputs. Humans and animals rely on plants for their reduced sulfur, and plant sulfur nutrition has a decisive effect on food quality, e.g., availability of methionine, breadmaking and malting quality, and on health, because some secondary sulfur compounds have significance as phytopharmaceuticals. A balanced sulfur diet is essential in animal feeding and deficiency negatively affects sheep wool production, though excessive sulfur may induce copper or selenium deficiency in cattle.