# Acoustic Emissions to Measure Drought-Induced Cavitation in Plants
## 5 Conclusions and Future Perspectives  
How plants cope with drought in a changing climate is an active area of research, but a lot of questions remain unanswered. Mechanisms and strategies that underlie plant survival and mortality during drought are the subject of an intense debate [9; 10; 11; 12; 13; 14; 15; 16]. The main drivers of this discussion are, however, the used methods instead of the actual mechanisms that occur in plants [39; 41; 110; 113]. Development of a universal technique to measure cavitation, and vulnerability to it, will be essential to bring the debate to a next level, which will change the focus towards physiology behind drought resistance. In this review, we showed that revival in the use of AEs for detection of plants' vulnerability to drought is very promising. It might become a powerful non-destructive, readily automated and online method. Although great advances were recently made in dealing with the main criticisms of the technique, such as being indirect and endpoint selection difficulties, further research is needed. The behavior of AEs in plant material has to be studied, and questions regarding wave propagation through wood, the behavior of dehydrating wood, and the mechanisms behind cavitation need to be answered in order to fundamentally link AEs and cavitation events. In order to achieve this, we recommend:* A combination of cavitation measurements with AE broadband sensors and \(\upmu\)CT in a broad range of plant species: interpretation of the acoustic signals in combination with visuals will govern the largest insights in the mechanisms underlying cavitation.
* Feature extraction from the AE signals: this will allow a comprehensive analysis of the AE sources, and will deliver valuable information on cavitation and other AE producing processes that occur in drought-stressed plants.
* Detailed study of wave propagation and attenuation in plants, both in dehydrating and in frozen samples.
* Investigation of the effects of debarking prior to acoustic measurements: as the bark can be an additional AE source, this might influence the captured signals.
* Further validation of the use of broadband point-contact AE sensors in the field of plant hydraulics _versus_ the 150 kHz resonance AE sensor.
* Development of an _in situ_ AE measurement protocol for living plants, and its translation to drought sensitivity.  
To conclude, the use of AEs in plant sciences to measure cavitation is promising and is gaining increasing interest. As implementation of some of the state-of-the-art techniques from material sciences already pushed frontiers in cavitation research, we believe that cross-fertilization between these different scientific domains will also be beneficial for both in the future.  
The authors thank the Research Foundation--Flanders (FWO) for funding (research program G.0941.15N granted to [PERSON], and PhD Fellowship granted to [PERSON]).  
[PERSON], [PERSON] and [PERSON] reviewed the literature. [PERSON] supervised the work. [PERSON] wrote most of the manuscript with the input of [PERSON], and all authors contributed by discussing and reviewing drafts and the final version of the manuscript. [PERSON] and [PERSON] contributed equally to the manuscript.  
The authors declare no conflict of interest.