arXiv subjects

Guillaume Charrier

Publications and source records attributed to Guillaume Charrier.

2 recordsLinked to original sources

arXiv2023

Xylem embolism and bubble formation during freezing suggest complex dynamics of pressure-tension in Betula pendula stems

Freeze-thaw-induced embolism is a key limiting factor for perennial plants in frost-exposed environments. Gas bubbles are formed during freezing and expand during thawing resulting in xylem embolism. However, when water freezes, its volume increases by 9%, generating local pressures, which can affect the formation of bubbles. To characterize local dynamic of pressure-tension and physical state of the sap during freeze-thaw cycles, we simultaneously used ultrasonic acoustic emissions analysis and synchrotron-based high resolution computed tomography on the diffuse-porous species Betula pendula. Visualization of individual air-filled vessels was performed to measure freeze-thaw induced embolism after successive freeze-thaw cycles down to -10°C or -20°C during the leafy and the leafless periods. We also measured the distribution of gas bubbles in frozen xylem of Betula pendula, and made additional continuous monitoring of embolism spreading during one freeze-thaw cycle using a dedicated cooling system that allowed X-ray scanning during freezing and thawing. Experiments confirmed that ultrasonic emissions occurred after the onset of ice formation, together with bubble formation, whereas the development of embolism took place after thawing in all cases. The pictures of frozen tissues indicated that the positive pressure induced by the volumetric increase of ice can provoke inward flow from the cell wall toward the lumen of the vessels. We found no evidence that wider vessels within a tissue were more prone to embolism although the occurrence of gas bubbles in larger conduits would make them prone to earlier embolism. These results highlight the need to monitor local pressure as well as ice and air distribution during xylem freezing to understand the mechanism leading to frost-induced embolism.

q-bio.TO↗

arXiv2021

Detection of acoustic events in Lavender for measuring the xylem vulnerability to embolism and cellular damages

Acoustic emission analysis is a promising technique to investigate the physiological events leading to drought-induced injuries and mortality. However, the nature and the source of the acoustic emissions are not fully understood and make the use of this technique difficult as a direct measure of the loss of xylem hydraulic conductance. In this study, acoustic emissions were recorded during severe dehydration in lavender plants and compared to the dynamics of embolism development and cell lysis. The timing and characteristics of acoustic signals from two independent recording systems were compared by principal component analysis. In parallel, changes in water potential, branch diameter, loss of hydraulic conductance and electrolyte leakage were measured to quantify drought-induced damages. Two distinct phases of acoustic emissions were observed during dehydration: the first one associated with a rapid loss of diameter and a significant increase in loss of xylem conductance (90%) and the second one with a significant increase in electrolyte leakage and slower diameter changes. This second phase corresponds to a complete loss of recovery capacity. The acoustic signals of both phases were discriminated by the third and fourth principal components. The loss of hydraulic conductance during the first acoustic phase suggests the hydraulic origin of these signals (i.e. cavitation events). For the second phase, the signals showed much higher variability between plants and acoustic systems suggesting that the sources of these signals may be plural, although likely including cellular damage. A simple algorithm was developed to discriminate hydraulic-related acoustic signals from other sources, allowing the reconstruction of dynamic hydraulic vulnerability curves. However, hydraulic failure precedes cellular damage and lack of whole plant recovery is associated to these latter.

q-bio.TO↗