New publication based on our living plant collection

The following publication was released on Nov. 10: Bouda, Martin, Brett A. Huggett, Kyra A. Prats, Jay W. Wason, Jonathan P. Wilson, and Craig R. Brodersen. 2022. Hydraulic failure as a primary driver of xylem network evolution in early vascular plants. Science 378, no. 6620: 642-646. link

The study integrated plants maintained in our Plant Biodiversity Conservatory and Research Core.

Significance of studySince plants colonized land, they have developed increasingly complex vessel architectures to carry water from their roots to their highest leaves. Vascular plants now display a diversity of xylem strand shapes in cross section, from elliptical to linear to many lobed. Bouda et al. investigated whether selection from drought, which causes vessel cavitation and embolism, drove the complexity of xylem strand shape as plants inhabited drier climates. By simulating embolism spread between vessels across varying shape and complexity, including those seen in extant lycophytes and ferns and extinct plant fossils, the authors found that evolutionary changes in xylem strand shape have reduced embolism spread and made plants less vulnerable to drought.

Abstract reads: The earliest vascular plants had stems with a central cylindrical strand of water-conducting xylem, which rapidly diversified into more complex shapes. This diversification is understood to coincide with increases in plant body size and branching; however, no selection pressure favoring xylem strand-shape complexity is known. We show that incremental changes in xylem network organization that diverge from the cylindrical ancestral form lead to progressively greater drought resistance by reducing the risk of hydraulic failure. As xylem strand complexity increases, independent pathways for embolism spread become fewer and increasingly concentrated in more centrally located conduits, thus limiting the systemic spread of embolism during drought. Selection by drought may thus explain observed trajectories of xylem strand evolution in the fossil record and the diversity of extant forms.