Biology subjects

Ameglio, T.

Publications and source records attributed to Ameglio, T..

4 recordsLinked to original sources

bioRxiv2024

Using fibre-optic sensing for non-invasive, continuous dendrometry of mature tree trunks

Dendrometry is the main non-invasive macroscopic technique commonly used in plant physiology and ecophysysiology studies. Over the years several types of dendrometric techniques have been developed, each with their respective strengths and drawbacks. Automatic and continuous monitoring solutions are being developed, but are still limited, particularly for non-invasive monitoring of large-diameter trunks. In this study, we propose a new type of automated dendrometer based on distributed fibre-optic sensing that continuously measures the change in stem circumference, is non-invasive, and has no upper limit on the trunk diameter on which it can be installed. We perform a three-month validation experiment during which we deploy a fibre-optic cable at three localities around the trunks of two specimens of Brachychiton. We verify the accuracy of this new method through comparison against a conventional point-dendrometer, and we observe a consistent time lag between the various measurement locations that varies with the meteorological conditions. Finally, we discuss the feasibility of the fibre-based dendrometer in the context of existing dendrometric techniques and practical experimental considerations.

plant biology↗

bioRxiv2023

On the mechanism for winter stem pressure build-up in walnut tree

Xylem embolism is a significant factor in tree mortality. Restoration of hydraulic conductivity after massive embolisation of the vascular system requires the application of positive pressure to the vessels and/or the creation of new conductive elements. Some species generate positive pressure from the root system to propagate pressure in distal, aboveground, organs in spring, whereas other species generate positive pressure locally at the stem level during winter. We provide a mechanistic explanation for winter stem pressure build-up in the walnut tree. We have developed a physical model that accounts for temperature fluctuations and phase transitions. This model is based on the exchange of water and sugars between living cells and vessels. Our computations demonstrate that vessel pressurization can be attributed to the transfer of water between vessels across the parenchyma rays, which is facilitated by a radial imbalance in sugar concentration. The ability to dispose of soluble sugars in living cells, and to transport them between living cells and up to the vessels, are identified as the main drivers of stem pressure build-up in the walnut tree.

plant biology↗

bioRxiv2023

Freeze dehydration vs. supercooling in tree stems: physical and physiological modelling

Frost resistance is the major factor affecting the distribution of plant species at high latitude and elevation. The main effects of freeze-thaw cycles are damage to living cells and formation of gas embolism in tree xylem vessels. Lethal intracellular freezing can be prevented in living cells by two mechanisms: dehydration and deep supercooling. We developed a multiphysics numerical model coupling water flow, heat transfer, and phase change, considering different cell types in plant tissues, to study the dynamics and extent of cell dehydration, xylem pressure changes, and stem diameter changes in response to freezing and thawing. Results were validated using experimental data for stem diameter changes of walnut trees. The effect of cell mechanical properties was found to be negligible as long as the intracellular tension developed during dehydration was sufficiently low compared to the ice induced cryostatic suction. The model was finally used to explore the coupled effects of relevant physiological parameters (initial water and sugar content) and environmental conditions (air temperature variations) on the dynamics and extent of dehydration. It revealed configurations where cell dehydration could be sufficient to protect cells from intracellular freezing, and situations where supercooling was necessary. This model, freely available with this paper, could easily be extended to explore different anatomical structures, different species and more complex physical processes.

biophysics↗

bioRxiv2019

Drought-induced mortality: stem diameter variation reveals a point of no return in lavender species

In the context of climate changes, water availability is expected to severely decline. Consequently, there is a need to predict mortality of woody species, especially to find a physiological threshold to drought-induced mortality. Lavender species (Lavandula angustifolia and Lavandula x intermedia) which are important crops of the Mediterranean region are affected by a decline, notably caused by successive intense drought events. Lavender response to extreme drought events was monitored using continuous stem diameter measurements. Water potential, stomatal conductance, loss of xylem hydraulic conductivity and electrolyte leakage were also measured during desiccation, and recovery was evaluated after rewatering. Two parameters computed from stem diameter variations were related to stress intensity and resilience to stress: PLD (Percentage Loss of Diameter) and stem PLRC (Percentage Loss of Rehydration Capacity of the stem), respectively. We showed that plants did not recover when the PLD reached its maximal value (PLDmax) which was 21.27 {+/-} 0.57% in both lavender species and whatever the growing conditions. This point of no return was associated with a high level of cell lysis evaluated by electrolyte leakage, and occurred far after the xylem hydraulic failure. We discussed the relevance of PLDmax as a threshold for drought-induced mortality and its physiological significance, in relation to the mortality mechanisms. One-sentence summaryUnder extreme drought, lavender death occurs when the water storage of the elastic compartment of the stem is exhausted.

plant biology↗