Increases in vein length compensate for leaf area lost to lobing in grapevine

There is considerable variation in leaf lobing and leaf size, including
among grapevines, some of the most well-studied leaves. We examined the
relationship between leaf lobing and leaf size across grapevine
populations which varied in extent of leaf lobing. We used homologous
landmarking techniques to measure 2,632 leaves across two years in 476
unique, genetically distinct grapevines from 5 biparental crosses which
vary primarily in the extent of lobing. We determined to what extent leaf
area could explain variation in lobing, vein length, and vein to blade
ratio. Although lobing was the primary source of variation in shape across
the leaves we measured, leaf area varied only slightly as a function of
lobing. Rather, leaf area increases as a function of total major vein
length, total branching vein length, and decreases as a function of vein
to blade ratio. These relationships are stronger for more highly lobed
leaves, with the residuals for each model differing as a function of
distal lobing. For a given leaf area, more highly lobed leaves have longer
veins and higher vein to blade ratios, allowing them to maintain similar
leaf areas despite increased lobing. These findings show how more highly
lobed leaves may compensate for what would otherwise result in a reduced
leaf area, allowing for increased photosynthetic capacity through similar
leaf size.