Rates of emission of H2S from plants and patterns of stable sulphur isotope fractionation

Abstract

In all green plants both HSO−3 and SO42− are reduced during photosynthesis, and many species can emit the product as H2S gas. Plants will emit H2S after fumigation with acute doses of SO2 gas1,2, irrigation with 5% K2SO4 solutions3, or immersion of roots in HSO−3 and SO42− solutions4. If such emissions of H2S by plants occur in nature, then this process adds sulphur to the atmosphere and contributes to the global sulphur budget. Oxidation of biogenic H2S in the atmosphere may also contribute to the formation of acid rain. We report here that irradiated plants with roots immersed in HSO−3 and SO42− solutions at concentrations found in nature emit H2S from their leaves, and that the fractionation of stable isotopes of sulphur during H2S emission may be useful for identifying atmospheric sulphur that has been generated by photosynthetic reduction of sulphur.