Scaling of angiosperm xylem structure with safety and efficiency

Abstract

We tested the hypothesis that greater cavitation resistance correlates with less total inter-vessel pit area per vessel (the pit area hypothesis) and evaluated a trade-off between cavitation safety and transport efficiency. Fourteen species of diverse growth form (vine, ring- and diffuse-porous tree, shrub) and family affinity were added to published data predominately from the Rosaceae (29 species total). Two types of vulnerability-to-cavitation curves were found. Ring-porous trees and vines showed an abrupt drop in hydraulic conductivity with increasing negative pressure, whereas hydraulic conductivity in diffuse-porous species generally decreased gradually. The ring-porous type curve was not an artifact of the centrifuge method because it was obtained also with the air-injection technique. A safety versus efficiency trade-off was evident when curves were compared across species: for a given pressure, there was a limited range of optimal vulnerability curves. The pit area hypothesis was supported by a strong relationship (r2 = 0.77) between increasing cavitation resistance and diminishing pit membrane area per vessel (A(P)). Small A(P) was associated with small vessel surface area and hence narrow vessel diameter (D) and short vessel length (L)--consistent with an increase in vessel flow resistance with cavitation resistance. This trade-off was amplified at the tissue level by an increase in xylem/vessel area ratio with cavitation resistance. Ring-porous species were more efficient than diffuse-porous species on a vessel basis but not on a xylem basis owing to higher xylem/vessel area ratios in ring-porous anatomy. Across four orders of magnitude, lumen and end-wall resistivities maintained a relatively tight proportionality with a near-optimal mean of 56% of the total vessel resistivity residing in the end-wall. This was consistent with an underlying scaling of L to D(3/2) across species. Pit flow resistance did not increase with cavitation safety, suggesting that cavitation pressure was not related to mean pit membrane porosity.

Allométrie du bois de cœur et de l’aubier pour sept espèces d’arbres tempérées chinoises

“…V), supporting the notion proposed by Meinzer et al (2005) but with a wider exponent range. This conclusion seems plausible because there are divergences in morphological and physiological properties of water conducting system for diverse species (Hacke et al, 2006). For example, conifer tracheids and angiosperm vessels can be substantial different in water conducting capacity (Hacke and Sperry, 2001).…”

Partitioning hydraulic resistance in Sorghum bicolor leaves reveals unique correlations with stomatal conductance during drought

“…Under this scenario, high r * OLV in leaves may facilitate whole-plant water conservation despite the hydraulic architecture of the remainder of the plant. The ability to tolerate low soil moisture and low leaf water potentials would be more important in xeric systems, and likely reflects characteristics of the individual vessel elements that limit cavitation (Wheeler et al 2005;Hacke et al 2006;Blackman et al 2010) and major vein density (Scoffoni et al 2011). Investigating how leaf resistances are partitioned in a widely distributed group of grasses would provide new insights into how leaf resistances contribute to plant distributions across the landscape.…”

A low cost apparatus for measuring the xylem hydraulic conductance in plants

“…Moreover, the development of highly negative water potentials increases the probability of bubble formation in the xylem, which interrupts the flow through vessels and may reduce the rate of photosynthesis and, consequently, growth (Tyree and Sperry, 1989). To avoid this problem, the hydraulic system can be more resistant to cavitation, and greater resistance is associated with lower porosity of the membrane between xylem vessels, which, in turn, reduces water flow efficiency (Hacke et al, 2006).…”