The fate of methyl salicylate in the environment and its role as signal in multitrophic interactions.

Phytohormones emitted into the atmosphere perform many functions relating to the defence, pollination and competitiveness of plants. To be effective, their atmospheric lifetimes must be sufficient that these signals can be delivered to their numerous recipients. We investigate the atmospheric loss processes for methyl salicylate (MeSA), a widely emitted plant volatile. Simulation chambers were used to determine gas-phase reaction rates with OH, NO3, Cl and O3; photolysis rates; and deposition rates of gas-phase MeSA onto organic aerosols. Room temperature rate coefficients are determined (in units of cm3 molecule-1 s-1) to be (3.20 ± 0.46) × 10-12, (4.19 ± 0.92) × 10-15, (1.65 ± 0.44) × 10-12 and (3.33 ± 2.01) × 10-19 for the reactions with OH, NO3, Cl and O3 respectively. Photolysis is negligible in the actinic range, despite having a large reported near-UV chromophore. Conversely, aerosol uptake can be competitive with oxidation under humid conditions, suggesting that this compound has a high affinity for hydrated surfaces. A total lifetime of gas-phase MeSA of 1-4 days was estimated based on all these loss processes. The competing sinks of MeSA demonstrate the need to assess lifetimes of semiochemicals holistically, and we gain understanding of how atmospheric sinks influence natural communication channels within complex multitrophic interactions. This approach can be extended to other compounds that play vital roles in ecosystems, such as insect pheromones, which may be similarly affected during atmospheric transport.