Above- and belowdround physiology in Vaccinium corymbosum L. (northern highbush blueberry) in response to water stress and reproductive effort.

Open Access
Valenzuela-Estrada, Luis Rene
Graduate Program:
Doctor of Philosophy
Document Type:
Date of Defense:
June 20, 2008
Committee Members:
  • David Eissenstat, Committee Chair
  • Daniel Dale Fritton, Committee Member
  • Roger Tai Koide, Committee Member
  • Elsa Selina Sanchez, Committee Member
  • root anatomy
  • root morphology
  • root architecture
  • hydraulic redistribution
  • minirhizotron
  • belowground carbon allocation
  • root lifespan
  • aboveground carbon dynamics
Vaccinium corymbosum L. (northern highbush blueberry) is a member of the Ericaceae family and of wide ecological and economic importance. However few studies have examined in detail whole-plant physiological responses to drought or reproductive effort. Belowground, one of the most studied aspects of members of the Ericaceae is their association with ericoid mycorrhizal fungi. Although not well studied, the root system of ericoid species is notable for being highly branched with its finest roots reaching only 20 µm in diameter. In this study, roots were classified and examined based on a root order classification, and anatomical, morphological and functional aspects were described. The root vascular anatomy and morphological data were then used to explore in more detail the response of this root system to severe drought conditions and differences in reproductive growth. Using minirhizotrons, we examined root lifespan and seasonal patterns of root production. Even with such small diameters, the first three root orders (considered the ephemeral portion) exhibited median lifespans between 115-155 d. By exposing the root system to heterogeneous soil water conditions and soil water deficits, patterns of nocturnal root tissue rehydration for each root order were studied by measuring their water potentials using thermocouples psychrometers over the nighttime period of 12 h. We hypothesized that root tissue rehydration would be delayed, especially in the distal root orders because of their greater hydraulic constrains. We found that even though the water potentials of roots in dry soil equilibrated with those of roots in wet soil, the equilibrium point reached before sunrise was still about -1.2 MPa, indicating tissues were not fully rehydrated. The finest distal roots (1st –order roots) exhibited the lowest water potentials in dry soil. The lowest root hydraulic resistances (estimated) corresponded to the lowest orders of the permanent root system (4th-order roots), thus, indicating a possible place of hydraulic safety control. Reproductive effort can strongly influence processes belowground. Mycorrhizal colonization increased as reproductive effort increased. However, fine root dynamics (production and lifespan) and physiological traits such as root respiration, total nonstructural carbohydrate concentration, and root membrane leakage were not affected by high reproductive effort, suggesting a root system with a very low cost of construction and maintenance. The first three root orders account for < 16% of the total plant non-structural biomass. In contrast, high reproductive effort caused a 53% difference in total aboveground plant non-structural biomass at the time of maximum fruit growth compared with non-fruited plants. A slight increase in photosynthetic rates and a very low carbon requirement belowground may be associated with the high carbon efficiency of Vaccinium corymbosum coping with the high C and N demands associated with high reproductive effort.