A constructed wetland microcosm was employed to investigate the sulfur cycle-mediated electron transfer between carbon and nitrate.Sulfate accepted electrons from organics at the average rate of 0.84 mol/(m3.d) through sulfate reduction,which accounted for 20.0％ of the electron input rate.The remainder of the electrons derived from organics were accepted by dissolved oxygen (2.6％),nitrate (26.8％),and iron(Ⅲ) (39.9％).The sulfide produced from sulfate reduction was transformed into acidvolatile sulfide,pyrite,and elemental sulfur,which were deposited in the substratum,storing electrons in the microcosm at the average rate of 0.52 mol/(m · d).In the presence of nitrate,the acid-volatile and elemental sulfur were oxidized to sulfate,donating electrons at the average rate of 0.14 mol/(m3· d) and driving autotrophic denitrification at the average rate of 0.30 g N/(m · d).The overall electron transfer efficiency of the sulfur cycle for autotrophic denitrification was 15.3％.A mass balance assessment indicated that approximately 50％ of the input sulfur was discharged from the microcosm,and the remainder was removed through deposition (49％) and plant uptake (1％).Dominant sulfatereducing (i.e.,Desulfovirga,Desulforhopalus,Desulfatitalea,and Desulfatirhabdium) and sulfuroxidizing bacteria (i.e.,Thiohalobacter,Thiobacillus,Sulfuritalea,and Sulfurisoma),which jointly fulfilled a sustainable sulfur cycle,were identified.These results improved understanding of electron transfers among carbon,nitrogen,and sulfur cycles in constructed wetlands,and are of engineering significance.