Rootstocks induce functional differences that affect carbon isotope
discrimination and water relations in the apple scion
Abstract
Composite trees combine traits from both the rootstock and scion.
Dwarfing rootstocks are used to reduce shoot vigor and improve fruit
quality and productivity. Although differences in rootstock vigour have
been clearly described, the underlying physiological mechanisms
regulating scion vigor are not well understood. Plant water status is
strongly influenced by stem hydraulic resistance to water movement. In
the scion, stomata regulate transpiration rates and are essential to
prevent hydraulic failure. Lower stomatal conductance contributes to
enriched leaf carbon isotope composition (δ13C). Combined, the effects
of increased hydraulic resistance, limited stomatal control, and
subsequently, limited gas exchange can affect tree growth. These
differences may also correspond to differences in scion vigor. Here,
vegetative growth, gas exchange, stem water potential, and leaf δ13C
were compared to determine how rootstocks affect scion water relations.
B.9 had the lowest shoot vigor compared to the more vigorous rootstock,
G.890. Similarly, photosynthetic rates were also lower. Rootstock vigor
was closely associated with leaf gas exchange and stem water potential
in the scion and were reflected in leaf δ13C signatures. Dwarfing was
strongly related to hydraulic limitations induced by rootstock genotype
and these changes are distinguishable when measuring leaf and stem δ13C
composition.