In what forms do plants and animals excrete sulfur?
Sulfur is $3^{rd}$ most abundant mineral element in the body. Carnivores obtain it from Cysteine and Methionine in the animal protein which converted in to Glutathione.
Excess of sulfur is stored into Glutathione or oxidised to sulfate by sulfite oxidase which is eventually eliminated by urine.



[1]: Nimni ME, Han B, Cordoba F (2007). "Are we getting enough sulfur in our diet?". Nutr Metab (Lond) 4 (1): 24. doi:10.1186/1743-7075-4-24

[2]: Wikipedia on Sulfur metabolism