Chloromethane formation and degradation in the fern phyllosphere.

Chloromethane (CH 3 Cl) is the most abundant halogenated trace gas in the atmosphere. It plays an important role in natural stratospheric ozone destruction. Current estimates of the global CH 3 Cl budget are approximate. The strength of the CH 3 Cl global sink by microbial degradation in soils and plants is under discussion. Some plants, particularly ferns, have been identified as substantial emitters of CH 3 Cl. Their ability to degrade CH 3 Cl remains uncertain. In this study, we investigated the potential of leaves from 3 abundant ferns ( Osmunda regalis , Cyathea cooperi , Dryopteris filix-mas ) to produce and degrade CH 3 Cl by measuring their production and consumption rates and their stable carbon and hydrogen isotope signatures. Investigated ferns are able to degrade CH 3 Cl at rates from 2.1 to 17 and 0.3 to 0.9 μg g dw −1 day − 1 for C. cooperi and D. filix-mas respectively, depending on CH 3 Cl supplementation and temperature. The stable carbon isotope enrichment factor of remaining CH 3 Cl was −39 ± 13‰, whereas negligible isotope fractionation was observed for hydrogen (−8 ± 19‰). In contrast, O. regalis did not consume CH 3 Cl, but produced it at rates ranging from 0.6 to 128 μg g dw −1 day − 1 , with stable isotope values of −97 ± 8‰ for carbon and −202 ± 10‰ for hydrogen, respectively. Even though the 3 ferns showed clearly different formation and consumption patterns, their leaf-associated bacterial diversity was not notably different. Moreover, we did not detect genes associated with the only known chloromethane utilization pathway “ cmu ” in the microbial phyllosphere of the investigated ferns. Our study suggests that still unknown CH 3 Cl biodegradation processes on plants play an important role in global cycling of atmospheric CH 3 Cl. [ABSTRACT FROM AUTHOR]