The ‘hydrology’ of leaves: co‐ordination of structure and function in temperate woody species

Abstract

The hydraulic conductance of the leaf lamina ( K lamina ) substantially constrains whole-plant water transport, but little is known of its association with leaf structure and function. K lamina was measured for sun and shade leaves of six woody temperate species growing in moist soil, and tested for correlation with the prevailing leaf irradiance, and with 22 other leaf traits. K lamina varied from 7.40 ¥ ¥ ¥ ¥ 10-1 for Vitis labrusca sun leaves. Tree sun leaves had 15-67% higher K lamina than shade leaves. K lamina was co-ordinated with traits associated with high water flux, including leaf irradiance, petiole hydraulic conductance, guard cell length, and stomatal pore area per lamina area. K lamina was also co-ordinated with lamina thickness, water storage capacitance, 1/mesophyll water transfer resistance, and, in five of the six species, with lamina perimeter/area. However, for the six species, K lamina was independent of inter-related leaf traits including leaf dry mass per area, density, modulus of elasticity, osmotic potential, and cuticular conductance. K lamina was thus co-ordinated with structural and functional traits relating to liquid-phase water transport and to maximum rates of gas exchange, but independent of other traits relating to drought tolerance and to aspects of carbon economy.

Hydraulic Analysis of Water Flow through Leaves of Sugar Maple and Red Oak

“…Across plant species, R leaf is negatively coordinated with peak rates of gas exchange (Aasamaa et al, 2001;Sack et al, 2003b). The importance of the vein system in determining R leaf , as found in this study, suggests potentially important functional consequences at the whole-leaf and plant level for the diversity of leaf venation architecture in angiosperms (Roth-Nebelsick et al, 2001), i.e.…”

“…The hydraulic resistance remaining was considered that of the major veins (R major veins ), and R minor veins was calculated as R venation ÿ R major veins . Because the petiole must be severed and recut so that it can be sealed to the flow meter, R petiole was estimated using the resistance of the petiole segment divided by its length and then multiplied by the intact petiole length, as estimated using regressions of petiole length versus leaf area (Sack et al, 2003b). Estimates of R petiole were normalized by leaf area to have the same units as R lamina .…”

“…The leaf hydraulic resistance (R leaf ) constitutes a significant hydraulic bottleneck, correlates with leaf structure, and apparently constrains gas exchange (Tyree and Zimmermann, 2002;Sack et al, 2003b;Sack and Tyree, 2004). R leaf is an aggregate measure; once past the petiole, water flows through a reticulate network of veins, across the bundle sheath cells, and through or around mesophyll cells before evaporation and diffusion from the stomata (Esau, 1965).…”

Evolution of C 4 plants: a new hypothesis for an interaction of CO 2 and water relations mediated by plant hydraulics

“…However, we note that a lower K stem does not necessarily imply a lower K plant ; indeed, a higher leaf hydraulic conductance (K leaf ) can easily compensate. Recent work has shown the leaf is a critical bottleneck in the whole-plant hydraulic pathway, accounting for greater than 30 per cent of whole plant resistance, and that leaves have steeper hydraulic vulnerability curves than stem [96]. Consequently, K leaf is a strong determinant of K plant , especially when leaves begin to dehydrate during transpiration or incipient drought [97][98][99][100][101].…”

How Does Leaf Anatomy Influence Water Transport outside the Xylem?

“…Mesophyll tissue thickness and the ratio of spongy to palisade mesophyll tissue thickness are also both correlated with K leaf (for a comprehensive review of anatomical determinants of K leaf , see Sack et al, 2015). Additionally, across species, mesophyll anatomy, venation architecture, stomatal conductance, and K leaf tend to be intercorrelated (Sack et al, 2003;Aasamaa et al, 2005;Brodribb and Jordan, 2008;Carins Murphy et al, 2012Brodribb et al, 2013;Feild and Brodribb, 2013). Thus, many of the key anatomical traits that may influence K ox tend to be highly correlated across species , making it difficult to infer causal relationships.…”