Sulfur Fertilization and Fungal Infections Affect the Exchange of H2S and COS from Agricultural Crops

The emission of gaseous sulfur (S) compounds by plants is related to several factors, such as the plant S status or fungal infection. Hydrogen sulfide (H2S) is either released or taken up by the plant depending on the ambient air concentration and the plant demand for S. On the contrary, carbonyl sulfide (COS) is normally taken up by plants. In a greenhouse experiment, the dependence of H2S and COS exchange with ambient air on the S status of oilseed rape (Brassica napus L.) and on fungal infection with Sclerotinia sclerotiorum was investigated. Thiol contents were determined to understand their influence on the exchange of gaseous S compounds. The experiment revealed that H2S emissions were closely related to pathogen infections as well as to S nutrition. S fertilization caused a change from H2S consumption by S-deficient oilseed rape plants to a H2S release of 41 pg g(-1) (dw) min(-1) after the addition of 250 mg of S per pot. Fungal infection caused an even stronger increase of H2S emissions with a maximum of 1842 pg g(-1) (dw) min(-1) 2 days after infection. Healthy oilseed rape plants acted as a sink for COS. Fungal infection caused a shift from COS uptake to COS releases. The release of S-containing gases thus seems to be part of the response to fungal infection. The roles the S-containing gases may play in this response are discussed.