Xylem embolism refilling revealed in stems of a weedy grass

Authors: STEWART, JARED - Collaborator; Allen, Brendan; Polutchko, Stephanie; OCHELTREE, TROY - Colorado State University; Gleason, Sean

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2025
Publication Date: 3/20/2025
Citation: Stewart, J.J., Allen, B.S., Polutchko, S.K., Ocheltree, T.W., Gleason, S.M. 2025. Xylem embolism refilling revealed in stems of a weedy grass. Proceedings of the National Academy of Sciences (PNAS). 122(13). https://doi.org/10.1073/pnas.2420618122.
DOI: https://doi.org/10.1073/pnas.2420618122

Interpretive Summary: Gas bubbles forming in the water-conducting parts of plants, known as embolism, are considered a major threat to plant growth and survival during drought. This problem affects forests, grasslands, and crops. However, scientists don't agree on whether embolism can be reversed or refilled once it happens in the plant's water transport system, the xylem. This uncertainty makes it hard to predict how natural or engineered resistance to embolism will impact plant resilience to climate change. The xylem's structure and function make this question difficult to study. Water moves from the soil to the leaves under very high pressure, which is hard to recreate in experiments that involve cutting or manipulating the xylem. Using new high-resolution x-ray microcomputed tomography, we show for the first time that embolism can be completely reversed in monocotyledon xylem. We also measured the timing of this refilling process and checked the stability of the refilled conduits one day and ten days after re-watering.

Technical Abstract: Gas formation within the water conducting elements of vascular plant species, i.e., embolism, is claimed to be the single most consequential obstacle to plant growth and survival during drought (Anderegg et al., 2016; Choat et al., 2018). Despite the potential adverse impact of embolism on forest, grassland, and agricultural systems, there is no consensus among scientists whether or not embolism can be reversed or “refilled” after arising in the water conducting tissues (xylem). This uncertainty has cast much doubt on how natural or engineered resistance to embolism among species might affect forest and crop resilience to climate change. Much of this uncertainty arises from the structural and physiological conditions of the xylem itself. Water is transported from the soil to the sites of evaporation under large negative pressure, far exceeding the vaporization pressure of liquid water at ambient temperature, i.e., in a metastable state. Such conditions are ill-suited for most xylem research methods, which require the physical manipulation of the xylem (cutting, scrapping, etc). Using newly developed high resolution x-ray microcomputed tomography methods, we demonstrate for the first time the complete reversal of embolism in both partially and fully embolized monocotyledon xylem. Furthermore, we quantify the timing of conduit refilling as well as the stability of refilled conduits one day and ten days after re-watering.