Vessel scaling in angiosperm leaves conforms with Murray’s law and area-filling assumptions

Authors: Gleason, Sean; BLACKMAN, CHRIS - Western Sydney University; GLEASON, SCOTT - Southwest Research Institute; MCCULLOH, KATHERINE - University Of Wisconsin; OCHELTREE, TROY - Colorado State University; WESTOBY, MARK - Macquarie University

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2018
Publication Date: 3/30/2018
Citation: Gleason, S.M., Blackman, C.J., Gleason, S.T., Mcculloh, K.A., Ocheltree, T.W., Westoby, M. 2018. Vessel scaling in angiosperm leaves conforms with Murray’s law and area-filling assumptions. New Phytologist. https://doi.org/10.1111/nph.15116.
DOI: https://doi.org/10.1111/nph.15116

Interpretive Summary: Vessel scaling in angiosperm leaves conforms with Murray’s law and area-filling assumptions: implications for leaf size, aridity, and cold tolerance Abstract • It is predicted from theory that the thickness and number of vessels (water-transporting “pipes” in flowering plants) in plant tissues should correlate to one another (i.e., “scale” with one another) in a way that results in maximal conductance of the entire vessel network. It is also predicted that we might expect shifts in vessel scaling across aridity and temperature gradients. • We measured the change in vessel width and number in the leaves of 36 species spanning a large range in aridity and temperature in eastern Australia, and evaluate the degree of divergence in vessel scaling across these species and habitats. • The scaling of vessel width and number did not differ across species and habitats (P > 0.807), and did not differ from that predicted from maximal conductance theory (Murray’s law). Leaf size was strongly correlated with the thickness of vessels and did not differ among habitats, nor did the scaling differ significantly from that predicted from Murray’s law. • The thickness of vessels in leaves was related to the temperature of a species’ habitat and suggests that temperature sets a limit on the maximum thickness of vessels (and therefore the achievable plant/leaf size) in a given habitat.

Technical Abstract: • Hydraulic theory predicts convergent and predictable scaling of conduit width and number across species; however, it has also been suggested that we might expect shifts in vessel scaling across aridity and temperature gradients. • We measured the change in vessel width and number between the midrib and 2° veins across 36 evergreen Angiosperms spanning a large range in aridity and temperature in eastern Australia, and evaluate the degree of divergence in vessel scaling across species and habitats. • The scaling of vessel width and number did not differ across species and habitats (P > 0.807), and did not differ from that predicted by Murray’s law (P > 0.301). Leaf size was strongly correlated with the hydraulic radii in petioles (r2 = 0.82, P < 0.001) and did not differ among habitats (P > 0.078), nor did the scaling exponent differ significantly from that predicted from Murray’s law or the area-filling principal derived from allometric scaling theory (P = 0.367). • Hydraulic radii in leaf petioles was correlated with the temperature of the coldest quarter (r2 = 0.67; P < 0.001) and suggests that temperature sets a limit on the maximum hydraulic radii (and therefore the achievable plant/leaf size) in a given habitat.