Non-invasive imaging of drought-induced cavitation in plants

Abstract

The increased frequency of extreme events, associated with climate change, can lead to loss of biodiversity and forest dieback. Intense drought has disastrous effects on plants growth and physiology and maintaining hydraulic conductivity during time of water stress is necessary for plants survival. However, during drought, the blockage of the hydraulic pathway by air-seeding results in the loss of conductivity by embolism formation. Therefore, it is essential to be able to accurately measure the conductivity, leading to a better prediction of species vulnerability through vulnerability curves (VCs). The measure of vulnerability thresholds is necessary in order to evaluate the causes of forests dieback. Moreover, understanding the mechanisms behind drought-recovery and embolism repair can contribute to the advance of models used to predict the impact of drought on vegetation dynamics. This PhD was designed to test the accuracy and applicability of new visual techniques and aim to provide alternatives to invasive methods for measure of VCs. While invasive techniques measure conductivity on cut samples, visual techniques allow for measurements on intact samples. However, the question of the accuracy of visual methods are still discussed on the ground that they do not provide a direct measurement of conductivity (PLC) but instead use a proxy through the measurements of loss of vessels (PLV). In conclusion, my PhD research addresses the use of visual techniques as an accurate alternative for invasive methods and aims to provide further knowledge concerning mechanisms that regulates drought-induced embolism and recovery, under controlled conditions as well as in field-based studies. The results of this research suggest that (1) visual techniques may be used with all xylem anatomy, but need precise implementation in order to avoid erroneous results, (2) embolism repair via refilling is not a common for E. saligna and severe drought may be responsible for lagged-mortality also observed in the field and that (3) hydraulic failure driven by drought-induced embolism was one of the factors that contributed to the massive dieback of A. marina in northern Australia. Overall, drought-induced embolism may lead to forest mortality and lagged-mortality in many ecosystems, and the understanding of species dependant embolism recovery responses is necessary to determine species resistance and resilience to extreme events and climate change.

Date of Award	2021
Original language	English