How do leaf veins influence the worldwide leaf economic spectrum? Review and synthesis

Abstract

Leaf vein traits are implicated in the determination of gas exchange rates and plant performance. These traits are increasingly considered as causal factors affecting the 'leaf economic spectrum' (LES), which includes the light-saturated rate of photosynthesis, dark respiration, foliar nitrogen concentration, leaf dry mass per area (LMA) and leaf longevity. This article reviews the support for two contrasting hypotheses regarding a key vein trait, vein length per unit leaf area (VLA). Recently, Blonder et al. (2011, 2013) proposed that vein traits, including VLA, can be described as the 'origin' of the LES by structurally determining LMA and leaf thickness, and thereby vein traits would predict LES traits according to specific equations. Careful re-examination of leaf anatomy, published datasets, and a newly compiled global database for diverse species did not support the 'vein origin' hypothesis, and moreover showed that the apparent power of those equations to predict LES traits arose from circularity. This review provides a 'flux trait network' hypothesis for the effects of vein traits on the LES and on plant performance, based on a synthesis of the previous literature. According to this hypothesis, VLA, while virtually independent of LMA, strongly influences hydraulic conductance, and thus stomatal conductance and photosynthetic rate. We also review (i) the specific physiological roles of VLA; (ii) the role of leaf major veins in influencing LES traits; and (iii) the role of VLA in determining photosynthetic rate per leaf dry mass and plant relative growth rate. A clear understanding of leaf vein traits provides a new perspective on plant function independently of the LES and can enhance the ability to explain and predict whole plant performance under dynamic conditions, with applications towards breeding improved crop varieties.

Weak coordination among petiole, leaf, vein, and gas‐exchange traits across Australian angiosperm species and its possible implications

“…2013; Feild and Brodribb 2013; Sack et al. 2013). Yet, it is equally important to understand why coordination among these traits is often weak or absent across species, as reported here and elsewhere (angiosperms in Brodribb and Holbrook 2006; Maherali et al.…”

“…2008; Sack et al. 2013). Taken together, we might expect coordination among the maximal capacity of petioles to transport water, the density of vein systems to distribute that water within the leaf, and the measured rates of gas exchange from the leaf surface.…”

Stomatal Conductance Is Essential for Higher Yield Potential of C3Crops

“…This review already emphasized (see Hypothesis 2) the relationship in soybeans with indeterminate growth habit between VLA and stomata density and maximal stomatal conductance (g max ) (Tanaka and Shiraiwa, 2009). It is possible that, as yield potentials were being increased, breeders unwittingly selected for high relative growth rates of upper leaves of plant canopies (see Hypothesis 2) characterized by higher VLA, higher leaf hydraulic conductance, higher rates of stomatal conductance and photosynthesis (Sack et al, 2013). Indeed, tight correlations between these parameters may be universal for vascular plants.…”

“…Furthermore, the recently formulated hypothesis of 'flux trait network' implies that the morphological parameter of 'vein length per unit leaf area' (VLA) strongly influences hydraulic conductance, and thus stomatal conductance, photosynthetic rate and plant relative growth rate (Sack et al, 2013). Independently, a strong association between "maximal stomatal conductance and the leaf vascular system's capacity to replace that water" has been verified (Brodribb et al, 2013).…”

“…Indeed, tight correlations between these parameters may be universal for vascular plants. It was documented for over 350 species of woody and herbaceous angiosperms (Sack et al, 2013) but also for early vascular plants such as 30 species of tropical ferns . In short, it is possible that plant breeders unwittingly hastened evolutionary processes that have been in place for a very long time.…”