The recurrent evolution of extremely resistant xylem

Highly resistant xylem has evolved multiple times over the past 400 million years.

Scott A M MacAdam & Amanda A Cardoso

Water is transported under tension in xylem and consequently is vulnerable to invasion by air and the formation of embolism. A debate has raged over whether embolism formation is non-reversible occurring at low water potentials or a regular diurnal occurrence that is non-lethal because of a capacity to refill embolised conduits.

This commentary is on a recent article, which utilised new non-invasive imaging techniques for assessing the formation of embolism in xylem, finding that the xylem of Laurus nobilis was highly resistant to the formation of embolism.

The recent results of this discovery are placed in the context knowledge from a diversity of species that has so far been identified with xylem similarly highly resistant to embolism formation.

The discovery that L. nobilis has xylem highly resistant to embolism formation adds to a body of literature suggesting that the resistance of xylem to embolism formation is a key adaptation utilised by many species native to seasonally dry environments. Highly resistant xylem has evolved numerous times across the angiosperm clade.

With more studies utilising similar observational and direct methods of assessing embolism resistance, further insight into the ecological and evolutionary relevance of this trait is imminent.

McAdam, S.A.M. & Cardoso, A.A. Annals of Forest Science (2019) 76: 2.


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