Leaf hydraulic capacity in ferns, conifers and angiosperms: impacts on photosynthetic maxima

Abstract

Summary• The hydraulic plumbing of vascular plant leaves varies considerably between major plant groups both in the spatial organization of veins, as well as their anatomical structure.• Five conifers, three ferns and 12 angiosperm trees were selected from tropical and temperate forests to investigate whether the profound differences in foliar morphology of these groups lead to correspondingly profound differences in leaf hydraulic efficiency.• We found that angiosperm leaves spanned a range of leaf hydraulic conductance from 3.9 to 36 mmol m 2 s − 1 MPa − 1 , whereas ferns (5.9 -11.4 mmol m − 2 s − 1 MPa − 1 ) and conifers (1.6 -9.0 mmol m − 2 s − 1 MPa − 1 ) were uniformly less conductive to liquid water. Leaf hydraulic conductance (K leaf ) correlated strongly with stomatal conductance indicating an internal leaf-level regulation of liquid and vapour conductances. Photosynthetic capacity also increased with K leaf , however, it became saturated at values of K leaf over 20 mmol m − 2 s − 1 MPa − 1 .• The data suggest that vessels in the leaves of the angiosperms studied provide them with the flexibility to produce highly conductive leaves with correspondingly high photosynthetic capacities relative to tracheid-bearing species.

Water Stress Deforms Tracheids Peripheral to the Leaf Vein of a Tropical Conifer

“…It was imagined that conifers might display more conservative stomatal regulation similar to ferns, which close their stomata before the onset of xylem dysfunction (Brodribb and Holbrook, 2004b). Such apparently risky behavior in conifers may be enabled by the large capacitance typically displayed by conifer leaves (Brodribb et al, 2005).…”

Anatomical and photosynthetic acclimation to the light environment in species with differing mechanisms of phloem loading

“…In fact, the capacity for transporting water (hydraulic conductance) has been related to photosynthetic capacity among different species (e.g., ref. 43). It is interesting that both pea and spinach, which do not show any increase in foliar vein density with growth at HL, are rather restricted in their tolerance for growing during the summer months in sites that experience high evaporative demand (i.e., they are known primarily as cool-weather crops).…”

Optimal vein density in artificial and real leaves

“…On warm, sunny days, the leaves of a large tree can transport hundreds of liters of water from the soil, corresponding to several milliliters per day per leaf. Although photosynthesis, rather than water loss, is the desideratum of living leaves, the shared diffusional pathway for CO 2 and water vapor and the regulation of this pathway by water status in the leaf implies that these two fluxes are closely coupled. Indeed, maximum rates of photosynthesis scale linearly with the transport capacity of the xylem (2)(3)(4).…”