The hydraulic conductance of the angiosperm leaf lamina: a comparison of three measurement methods

Abstract

A comparison was made of three methods for measuring the leaf lamina hydraulic conductance (K(lamina)) for detached mature leaves of six woody temperate angiosperm species. The high-pressure method, the evaporative flux method and the vacuum pump method involve, respectively, pushing, evaporating and pulling water out of the lamina while determining the flow rate into the petiole and the water potential drop across the leaf. Tests were made of whether the high-pressure method and vacuum pump method measurements of K(lamina) on single leaves were affected by irradiance. In Quercus rubra, the high pressure method was sensitive to irradiance; K(lamina) measured under high irradiance (>1200 micro mol m(-2) s(-1 )photosynthetically active radiation) was 4.6-8.8 times larger than under ambient laboratory lighting (approximately 6 micro mol m(-2) s(-1 )photosynthetically active radiation). By constrast, the vacuum pump method was theoretically expected to be insensitive to irradiance, and this expectation was confirmed in experiments on Hedera helix. When used in the ways recommended here, the three methods produced measurements that agreed typically within 10%. There were significant differences in species' K(lamina); values ranged from 1.24x10(-4) kg s(-1) m(-2) MPa(-1) for Acer saccharum to 2.89x10(-4) kg s(-1) m(-2) MPa(-1) for Vitis labrusca. Accurate, rapid determination of K(lamina) will allow testing of the links between K(lamina), water-use, drought tolerance, and the enormous diversity of leaf form, structure and composition.

Conductancia hidráulica foliar y vulnerabilidad a la cavitación disminuyen con la altitud en Phacelia secunda J.F. Gmel. (Boraginaceae)

“…Las hojas fueron puestas en agua dentro del matraz, para asegurarse de que no hubiera pérdida de agua por evaporación durante las mediciones. Además, para no tener problemas con el cierre estomático (Sack et al 2002), las hojas fueron mantenidas a la luz antes y durante el experimento.…”

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

“…The use of this apparatus and its conductance measurements enables us to compare the different characteristics of the plant with its hydraulic system. With few adaptations in the apparatus, the method with vacuum can be applied to measure the root conductance, stem and leaves, as shown by several authors (Kolb et al, 1996;Sack et al, 2002;Tyree et al, 2002;2003;Kursar et al, 2009;Melcher et al, 2012). We have also successfully used our assembled apparatus to determine the conductance in stems, roots and leaves of other species like coffee and citrus (unpublished data).…”

“…A direct estimate of conductance can be obtained by measuring the flow of a solution through a segment of the plant, which is caused by a pressure difference (ΔP), from 3-10 kPa, between the "inlet" and "outlet" of the branch or root (Sperry et al, 1988). This pressure difference can be applied using the height of the water column connected to the plant segment.…”

“…Conversely, the flow direction is reversed for the roots, in which the radicular branches are suctioned as "outlets" and the "inlet" is the connection with the stem. Thus, this apparatus is inverted compared with the apparatus proposed by Sperry et al (1988), which considers the mass of the solution suctioned through the branch or root. The reverse flow, in relation to the flow in intact plant, has no effect on the conductance (Sperry et al, 1988;Kolb et al, 1996).…”

“…Cavitation resistance can be evaluated by comparing the conductance measurements of a desiccated plant at different water potentials in xylem and measurements after the treatment to remove bubbles from the xylem (Sperry et al, 1988). The difference between the maximum conductance (after treatment) and conductance of the desiccated plant (initial) can be represented as the percentage loss of conductance.…”