Sulfur – Interactions with Other Nutrients and Stress Tolerance
Sulfur nutrition has become an area of intense research recently. Scientists know that sulfur is required by plants to produce two sulfur-containing amino acids (methionine and cysteine) that are necessary for protein production, and if adequate levels are not available, there will be decreased productivity. Less frequently discussed is the interaction between sulfur and other nutrients, and the need for adequate sulfur for the crop to mount a response to various stresses.
A journal publication on the role of sulfur nutrition on various aspects of crop production was published in July 2021, and it can be accessed for free. There is another article, published in 2015, available online that discusses the specific topic of stress tolerance.
Inadequate sulfur supply can affect the efficient use of other nutrients. The clearest example is nitrogen. In fact, many times nitrogen and sulfur requirement are considered as a ratio when it comes to making recommendations or when evaluating tissue concentrations. As mentioned earlier, adequate sulfur is required to produce two amino acids. These amino acids are critical to the production of protein. What other nutrient is synonymous with protein? Nitrogen. Thus, it makes sense that sulfur and nitrogen are linked. They are so linked that higher rates of nitrogen fertilization can induce more sulfur deficiency when sulfur supply is limited compared to lower nitrogen rates.
Additional research points to sulfur interactions with phosphorus, potassium, zinc, and boron (see the 2021 article referenced above). Interestingly most of this research has been conducted on soybean, cluster bean, chickpeas, and groundnut (all legumes). In conclusion, adequate sulfur nutrition is important to ensure efficient use of other nutrients available to a crop.
Adequate sulfur nutrition is also important for several sulfur-containing compounds that deal with the plant’s response to abiotic and biotic stresses. What are abiotic stresses? Stresses that are not attributable to another biological entity. These would include heavy metal exposure, salt stress, moisture stress, temperature stress, etc. Biotic stresses are directly attributable to a biological entity. These would include insect feeding, pathogenic infection (viral, bacterial, or fungal), nematode feeding, etc.
The compounds that are specifically involved in stress response to abiotic stresses that contain sulfur are glutathione and thioredoxin. A little hint, anytime you see “thio,” that indicates the presence of sulfur, so these two compounds require sulfur to be present in adequate amounts to maximize stress response. The typical abiotic stresses that glutathione and thioredoxin respond to are heavy metal exposure (including exposure to high amounts of required metals – zinc and copper) and salt stress. Glutathione is a precursor to the production of compounds capable of chelating reactive oxygen species that cause oxidative damage to cells. Thioredoxin plays a similar role by scavenging reactive oxygen species that can cause oxidative damage. In lay terms, these sulfur-containing chelating compounds keep harmful products from injuring cells.
Sulfur-containing compounds are also useful in helping a plant respond to biotic stresses. Oddly enough, glutathione appears again as a plant’s response to pathogen infection. Other sulfur-containing compounds that are utilized in a plant’s response to biotic stress are glucosinolates and the amino acid cysteine. Some species in the Brassica genus, a genus with generally high glucosinolate content, are known to resist certain pests and may even be used as “trap crops” for some pests, such as certain types of nematodes.
In conclusion, make certain that your crop has an adequate level of sulfur available to allow for efficient use of other nutrients to maximize biomass accumulation and ultimately yield. Additionally, adequate sulfur nutrition can also allow the plant to respond to various stress factors that impact cellular activity protecting the yield that is achievable. Like we have mentioned in other articles, be particularly vigilant on soils that are coarse textured and low in organic matter in high rainfall environments or northern latitudes with considerable surface residue that slows soil mineralization rate (articles: Sulfur: The Other Essential Soil Nutrient and Managing Sulfur for Spring Wheat in the Red River Valley). High-sulfur-demanding crops should also be evaluated for sulfur supplementation. Also be on the lookout for visual signs of sulfur deficiency to be a clue for where active sulfur supplementation is required.
