Fluxes of atmospheric hydrogen sulphide to plant shoots.

Short-term exposure of maize, pumpkin, spinach and spruce to various atmospheric H2S concentrations resulted in high H2S fluxes to the shoots. In all species an almost linear relation was observed between flux and H2S concentration up to around 0.3 myl 1 high minus 1. At higher H2S concentration the flux reached a maximum which was about 0.08, 0.04, 0.1 and 0.03 mymol g f.wt high minus 1 h high minus 1 for maize, pumpkin, spinach and spruce respectively. The transpiration rate was not affected during H2S exposure. Up to a level of 0.3 myl 1 high minus 1, the shoot conductance for H2S influx of the various species varied between 61 and 92% of that predicted from shoot conductance for aqueous vapour efflux. There was no relation between the H2S flux to the shoots and the sensitivity of the species towards H2S. A 12 days' exposure of maize, pumpkin and spinach to 0.75 myl 1 high minus 1 H2S resulted in a reduction of shoot yield of 1,36 and 69%, respectively. H2S flux to the shoots of pum pkin, spinach and spruce remained rather constant during exposure for three days to about 0.22 myl 1 high minus 1 H2S. Even at a concentration of about 0.8 myl 1 high minus 1 H2S, which reduced the growth of pumpkin and spinach, the fluxes remained nearly constant. Fluxes of H2S to the shoots did, however, vary diurnally, being high during the light and low during the dark period. The H2S flux to transpiration ratio was constant during both light and dark periods, indicating that uptake was predominantly via the stomata. Only part of the total flux.