EXCHANGE OF CARBONYL SULFIDE (COS) BETWEEN AGRICULTURAL PLANTS AND THE ATMOSPHERE - STUDIES ON THE DEPOSITION OF COS TO PEAS, CORN AND RAPESEED

Young corn, pea and rapeseed plants were exposed to compressed synthetic air containing varying COS concentrations. The results suggest that COS exchange depends highly on the ambient COS mixing ratios. Ambient COS mixing ratios larger than 150 pptv resulted in a deposition of COS to all plant species studied. Significant (confidence level 95%) COS emission was only detected from rapeseed leaves at COS mixing ratios lower than 90 pptv. We computed COS compensation points around 90 (57-135) pptv and 144 (0-328) pptv COS for rapeseed and corn. For both plant species we found a close correlation between the photosynthetic CO2 assimilation and the COS uptake. In contrast to the gas exchange studies with corn and rapeseed, experiments with pea plants revealed neither a change in response to increased COS concentrations of between 350 and 900 pptv COS nor any correlation with photosynthesis. However, for all three plants studied we found indications that COS is taken up preferentially over CO2 under normal ambient conditions.