Rootstocks induce functional differences that affect carbon isotope discrimination and water relations in the apple scion
Erica Casagrande Biasuz; Lee A. Kalcsits
Department of Horticulture, Tree Fruit Research and Extension Center, Washington State University, 1100 North Western Avenue, Wenatchee, WA 98801
This research was funded by the U.S. Department of Agriculture (USDA), National Institute of Food and Agriculture—Specialty Crop Research Initiative project “AppleRoot2Fruit: Accelerating the development, evaluation, and adoption of new apple rootstocks” (2016-51181-25406).
Abstract
Composite trees combine optimal traits from both the rootstock and the scion. Dwarfing rootstocks are commonly used to reduce shoot vigor and improve fruit quality and productivity. Although growth habits of different rootstocks have been clearly described, the underlying physiological mechanisms regulating scion vigor are not well understood. Plant water status and stem water potential are 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 and whether these differences correspond to shoot vigor. 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.
Keywords. Malus domestica, shoot vigor, carbon assimilation, stem water potential, dwarfing
Acknowledgments: We would like to acknowledge the support of Michelle Reid, Katie Mullin, and Hector-Camargo-Alvarez for technical assistance and the Washington State University Stable Isotope Laboratory for isotope analysis and support.
Rootstock-induced functional differences in the scion and its effect on carbon isotope discrimination and water relations in apple
Abstract
Composite trees combine optimal traits from both the rootstock and the scion. Dwarfing rootstocks are commonly used to reduce shoot vigor and improve fruit quality and productivity. Although growth habits of different rootstocks have been clearly described, the underlying physiological mechanisms regulating scion vigor are not well understood. Plant water status and stem water potential are 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 and whether these differences correspond to shoot vigor. 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.
Keywords: Malus domestica, rootstock, shoot vigor, carbon isotope, water relation