Plant volatiles in polluted atmospheres: stress responses and signal degradation

Abstract

Plants emit a plethora of volatile organic compounds, which provide detailed information on the physiological condition of emitters. Volatiles induced by herbivore feeding are among the best studied plant responses to stress and may constitute an informative message to the surrounding community and further function in plant defence processes. However, under natural conditions, plants are potentially exposed to multiple concurrent stresses with complex effects on the volatile emissions. Atmospheric pollutants are an important facet of the abiotic environment and can impinge on a plant's volatile-mediated defences in multiple ways at multiple temporal scales. They can exert changes in volatile emissions through oxidative stress, as is the case with ozone pollution. The pollutants, in particular, ozone, nitrogen oxides and hydroxyl radicals, also react with volatiles in the atmosphere. These reactions result in volatile breakdown products, which may themselves be perceived by community members as informative signals. In this review, we demonstrate the complex interplay among stresses, emitted signals, and modification in signal strength and composition by the atmosphere, collectively determining the responses of the biotic community to elicited signals.

Keywords: abiotic stress; biotic stress; cross-stress tolerance; induced volatiles; interactive stresses; multiple stresses; volatile-mediated interactions.

Fig. 1

Effects of pollutants on the fidelity and longevity of herbivore-induced volatile signals. A) Indicates the effects of pollutants on the blend of volatiles emitted in response to herbivore-feeding. B) Indicates the degradation of a volatile blend. C) Indicates the formation of secondary organic aerosols (SOA). The predicted effects of these processes on the blend composition (fidelity) and overall blend degradation (longevity) are represented by arrows. Arrow thickness indicates the predicted strength of effect with thicker arrows corresponding with a stronger effect.

Fig. 2

Transport, reaction, deposition and metabolism of volatiles after emission from plants. Volatile emission begins with the red arrow and movement of volatiles is represented by the dashed blue arrows. Reaction of VOCs with oxidants is represented by the line and plus sign. Solid lined arrows represent resulting products, RP denotes reaction products, MP denotes products of metabolism, MP-VOC denotes volatile products of metabolism and the SOA drawing represents secondary organic aerosol. The lines with round ends represent adsorption to surfaces. The line with a diamond at the end represents VOC uptake.