Methyl chloride ( CH 3 Cl ) and methyl bromide ( CH 3 Br ) emissions from economically important tropical crops

Tropical rainforests have recently been confirmed to be the largest source of methyl chloride and a missing source for methyl bromide. However, very few field studies have quantified methyl halide emissions from tropical plants. This study presents the first methyl halide emission measurements from 16 tropical crop species at the University of California, Berkeley Botanical Gardens. Leaf vial experiments qualitatively identified 15 out of the 16 species as CH3Cl emitters and 7 species as CH3Br emitters. Coffea arabica was the highest emitter for both CH3Cl and CH3Br. In addition, bag enclosure experiments were conducted on living plants to quantitatively determine net emission fluxes from C. arabica as well as a previous studied species, Angiopteris lygodiifolia. There were strong correlations between CH3Cl and CH3Br emission from both C. arabica and A. lygodiifolia, suggesting that the methyl halide productions share similar biological mechanisms in these species. Temperature observations also showed that methyl halide emissions from C. arabica strongly depended on temperature. Using the mean net emission flux, global CH3Cl emission by C. arabica was estimated to be 0.11 Tg yr, representing approximately 7.5% of the total CH3Cl emissions from tropical forests. Overall, the findings suggested that tropical crops make an important contribution to global terrestrial emissions of CH3Cl, but less so for CH3Br.