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Figure 4. a-c: Experimental setup configurations showing treatment (red) and control (green) root cups. A and B: number of seedlings that directed their roots toward the treatment side (white bars) across all test scenarios (scenarios TS1 to TS9). Gray bars, seedlings that did not choose the treatment side; red dashed lines, distinct scenarios. See text for more details. Reprinted from Gagliano et al., 2017, with permission.
contact, magnetism) is difficult, as is accurately replicat- ing the spectrum, amplitude, and temporal structure of the sound stimulus. There also remains the fundamental question as to whether plants are potentially responding to short-range mechanical vibration, near-field acoustic particle motion, or true acoustic sound, in the sense of a far-field airborne pres-
sure perturbation (ten Cate, 2013).
Despite these challenges, a growth spurt of new results over the past two decades has stimulated a parallel theoretical debate in the literature about potential underlying mecha- nisms for sound reception and response: alterations in gene transcription, soluble protein content, or other cellular level effects such as changes in the plasma membrane protein structure of microfilament rearrangements (Hilker et al., 2016; Mishra et al., 2016). The state of the discussion at pres- ent seems reminiscent of the arguments about continental drift at the turn of the twentieth century; there was empirical evidence that continents had shifted their positions in the past, but no one could provide a theoretical explanation into how granite-based continents could plow across basaltic sea floors. It remains uncertain where the present debate will go, but it seems certain that improved low-cost acoustic playback equipment and better experimental technique have added new fertilizer to some old questions.
Taking Root in the Acoustical Society of America
Plant bioacoustics covers many different fields of expertise and many different topics, but a consistent feature about most of this research is that the advent of modern signal processing has opened up many opportunities for field biologists to explore the topic. Another consistent feature is that very little of it has been presented at ASA confer- ences or published in The Journal of the Acoustical Society of America. Instead, the work has generally been presented in biological or agricultural journals. One wonders whether the current organization of the technical committees of the Society makes it difficult for plant bioacoustic research to find a natural venue, and if so, whether the society may be missing an opportunity to branch out into a new frontier of bioacoustics.
References
Appel, H. M., and Cocroft, R. (2014). Plants respond to leaf vibrations caused by insect herbivore chewing. Oecologia 175(4), 1257-1266.
De Luca, P. A., and Vallejo-Marín, M. (2013). What’s the ‘buzz’ about? The ecology and evolutionary significance of buzz-pollination. Current Opinion in Plant Biology 16(4), 429-435.
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