Air pollution impedes plant-to-plant communication, but what is the signal?

Abstract

Since the first reports that undamaged plants gain defensive benefits following exposure to damaged neighbors, the idea that plants may signal to each other has attracted much interest. There has also been substantial debate concerning the ecological significance of the process and the evolutionary drivers. Part of this debate has centered on the distance over which signaling between plants occurs in nature. In a recent study we showed that an ozone concentration of 80 ppb, commonly encountered in nature, significantly reduces the distance over which plant-plant signaling occurs in lima bean. We went on to show that degradation of herbivore-induced plant volatiles by ozone is the likely mechanism for this. The key question remaining from our work was that if ozone is degrading the signal in transit between plants, which chemicals are responsible for transmitting the signal in purer air? Here we present the results of a small scale experiment testing the role of the two most significant herbivore-induced terpenes and discuss our results in terms of other reported functions for these chemicals in plant-plant signaling.Plant-to-plant signaling mediated by volatile chemical compounds has been reported in numerous studies conducted under both laboratory 1,2 and field 3,4 conditions. It is one of the most sensitive volatile-mediated processes in nature and consequently the ecological significance of the phenomenon has been frequently questioned. 5 In addition, the evolutionary advantage of this process to the signal A range of volatile chemicals have been implicated as providers of inter-plant signals, including phytohormones such as methyl jasmonate, methyl salicylate and ethylene, various terpenes and green leaf volatiles (GLVs). 6 However, most of the underlying mechanisms, particularly concerning the perception of signal molecules, remain to be elucidated. 5 One of several outstanding questions related to airborne plant-plant signaling concerns the distance over which the signals are effective. The volatile chemicals that transmit signals between plants must remain intact and at sufficient concentration to be detected and elicit a response in receiver plants. The distances over which signal chemicals can function are limited by abiotic factors such as wind speed, air humidity and temperature.5 With respect to plant-plant interactions, much has been made about the effects of signal dilution in air currents, 5,7 but the degradation of the signaling compounds by reactive atmospheric pollutants can also represent a major obstacle to efficient plant-plant signaling. 6 The same can be said about other volatile mediated interactions including the attraction of predators, parasitoids and pollinators, and indeed some effects of ozone on foraging by parasitoids has been observed. 8 In a recent study, we showed that 80 ppb ozone significantly reduces the distance over which plant-plant communication is

Associational susceptibility in broccoli: mediated by plant volatiles, impeded by ozone

“…Elevated ozone eliminated the associational susceptibility, with P. xylostella not displaying a preference for either receiver plant. In earlier studies, it was shown that elevated ozone concentrations significantly reduce the distance of active plant–plant signalling in lima bean (Blande et al ., , ). It was reasoned that ozone could influence the between‐plant signalling process at one or more of three junctures.…”

Plant volatiles as cues and signals in plant communication

“…Degradation and formation of new products can alter the composition and ratio of key components in VOC profiles that reduce insect host location efficiency (Blande, Li, & Holopainen, 2011;Li, Blande, & Holopainen, 2016). All of these factors add a degree of complexity to the group of VOCs released as compared to the constitutive volatiles (Douma, Ganzeveld, Unsicker, Boeckler, & Dicke, 2019).…”

Ozone degrades floral scent and reduces pollinator attraction to flowers

“…Ozone can have significant negative impacts on plant reproductive success via its negative impacts on plant tissues and plant physiology (Bergweiler & Manning, ; Black et al ., ). Furthermore, many recent studies have reported that ozone and other common oxidative pollutants, such as hydroxyl and nitrate radicals, affect the emissions of VOCs from plants and the interactions they mediate (Pinto et al ., , ; McFrederick et al ., ; Blande et al ., , ; Fuentes et al ., ). Tropospheric ozone can affect plant emissions and their effectiveness in two ways: first, by affecting plant physiology and inducing changes in the emission profiles (Andermann et al ., ; Peñuelas & Llusia, ; Holopainen & Gershenzon, ), and second, by mixing and reacting with the emitted compounds once they are released (Holopainen & Blande, ; Blande et al ., ).…”