This journal article from Associate PhD Student Kate Johnson, Chief Investigator Tim Brodribb and colleague Christopher Lucani, involved monitoring a drought-resistant conifer, Callitris rhomboidea (Oyster Bay pine), to better understand how trees become damaged during drought events.
Drought kills trees of all species and ages, and there is knowledge gap around the mechanisms driving drought-induced tree death. Trees play a significant role in climatic regulation and terrestrial processes, with forest dieback increasing across the world and predictions of more frequent and severe drought events, understanding how trees die in drought is important.
Damage to the plant water transport system through the rapid formation of air bubbles which block water transport is known to be a driver of plant death in drought conditions. However, a lack of techniques to continuously monitor the plant water transport system inside whole living plants has hampered researchers’ ability to investigate how this damage spreads, and the possible link between plant water transport system damage and tissue death.
The researchers used optical and fluorescence sensors to monitor drought-induced air blockage accumulation and photosynthetic damage in the canopies of four Oyster Bay pine trees, for approximately 1 month per tree. They found that under drought conditions vulnerability of the plant water transport systems to air blockage varied widely among branchlets. It was observed that a large amount of air blockage is required to induce downstream tissue damage in conifer leaves. This experiment also demonstrated that an optical technique can be used to monitor air blockage accumulation continuously and non-destructively in living trees.
The variation in branchlet vulnerability observed in this study has important implications for understanding how trees survive drought and may be a strategy by which drought-resistant trees (like Oyster Bay Pine) survive and persist beyond drought. The high resistance of branchlets to tissue damage points to runaway air blockage accumulation as a likely driver of tissue death in the branch tips of Oyster Bay pine.
This same process of air bubble formation has been shown to be just as damaging to crop plants such as wheat, sorghum, and tomato, as it is for trees. Ongoing research in the Centre for Plant Success is aimed at understanding how this process affects crop behaviour, including resilience, biological life cycles, and yield. Collaboration in the Centre provides the connection to understanding the genetic basis of this important process, and the prospects for improving plant growth and resilience.
Set-up for optical embolism monitoring in Callitris rhomboidea saplings. (a) A branchlet prepared for embolism monitoring using the optical vulnerability technique, with the exposed xylem indicated by a white circle. (b) A MiCAM attached to a branchlet. (c) A tree with five MiCAMs attached and the shielded ICT stem psychrometer, which is attached to the main stem near the base of the tree (indicated by the orange arrow).
READ THE ARTICLE:
Johnson, K.M., Lucani, C. and Brodribb, T.J. (2021), In vivo monitoring of drought-induced embolism in Callitris rhomboidea trees reveals wide variation in branchlet vulnerability and high resistance to tissue death. New Phytologist. doi: 10.1111/nph.17786.
