Rootstock effects on xylem conduit dimensions and vulnerability to cavitation of Olea europaea L.

Abstract

Two clones of Olea europaea L. were studied for their potential impact on hydraulic architecture and vulnerability to xylem cavitation, when used as rootstocks. The clones used were ''Leccino Minerva'' (LM), showing vigorous growth and ''Leccino Dwarf'' (LD) with strongly reduced growth. Self-rooted LM and LD plants as well as their grafting combinations were compared, namely, LM/ LD (Leccino Minerva grafted onto Leccino Dwarf rootstock) and LD/LM (Leccino Dwarf grafted onto Leccino Minerva rootstocks). Plants with LD roots (LD and LM/ LD) showed significantly reduced leaf surface area compared with plants with LM roots. Xylem conduits of LD shoots were 25% more numerous than in LM shoots. When grafted onto LM rootstocks, however, LD shoots produced consistently wider and longer vessels than measured in LD self-rooted plants. This caused LD/LM plants to increase stem vulnerability to cavitation with threshold pressures for cavitation (P c ) of less than 0.5 MPa compared with LD self-rooted plants that had P c of over 2.0 MPa. By contrast, although LD rootstocks caused some reduction of vessel diameter and length of LM scions, their influence on LM hydraulic architecture was too small to reduce vulnerability to cavitation of LM scions with respect to that measured for LM self-rooted plants. Our conclusion is that although dwarfing rootstocks effectively reduce grafted plant size, they do not necessarily confer higher resistance to xylem cavitation to scions which would improve plant resistance to drought.

Wood anatomy and hydraulic architecture of stems and twigs of some Mediterranean trees and shrubs along a mesic-xeric gradient

“…High vulnerability of Q. ilex wood is in agreement with its sensitivity to aridity: although showing a plastic response to drought, mediated by changes of growth and wood features, after periods of severe drought this species probably suffers from widespread embolism which is responsible for dropping and reduced production of leaves (Corcuera et al 2004). However, as demonstrated in several Mediterranean species, the response of plants to changing water availability can be affected by other traits, such as root depth, root/ shoot ratio, interaction with rootstocks, inter-vessel pitting and physiological adjustments (Villar-Salvador et al 1997;Castro-Díez et al 1998;Vilagrosa et al 2003;Corcuera et al 2004;Martínez-Vilalta et al 2002;Trifilò et al 2007). Considering all measured characters as a whole, P. lentiscus would be the species that maintains the best balance between safety and efficiency in adult wood.…”

Shifts in xylem vessel diameter and embolisms in grafted apple trees of differing rootstock growth potential in response to drought

“…Rodriguez-Gamir et al 2010). According to the rootstock mediated growth regulation hypothesis, the act of grafting can alter xylem vessel diameters (Trifilò et al 2007). However, a proposed trade-off occurs as small increases in cross sectional xylem diameter result in proportionally larger decreases in conduit resistance to cavitation, jeopardizing water transport safety (Tyree and Zimmerman 2002).…”

“…To date, studies on water movement through grafted plants have focused on partitioning the hydraulic path as a means to better understand which plant organs play the largest role in restricting water flow (Berman and DeJong 1997;Cohen and Naor 2002;Nardini et al 2006;Cohen et al 2007). Empirical evidence has highlighted both negligible (Nardini et al 2006;Cohen et al 2007) and decreased (Atkinson et al 2003;Basile et al 2003;Gascó et al 2007;Gonçalves et al 2007;Trifilò et al 2007) changes in hydraulic resistance as a result of grafting. Decreased plant vigor through increased hydraulic resistance (restricted water flow) caused by the graft union and xylem conduit structure is widely accepted (Gonçalves et al 2007;Tombesi et al 2010).…”

“…Although cavitation and xylem vulnerability have been well studied in both woody and herbaceous plants, little information is available on anatomical plasticity and the accompanying shift in hydraulic conductivity of plants composed of scions grafted onto genetically different vigor controlling root systems (Trifilò et al 2007) under water limited conditions. Furthermore, we know of no studies that directly investigate the interaction between vigor controlling root systems and plant susceptibility to cavitation under decreased soil moisture conditions.…”

“…The aim of this study was to examine anatomical plasticity in response to limited water availability and to determine if there is a link between hydraulic responses to xylem vessel anatomy and direct measurements of xylem cavitation in both rootstock and scion portions of the plant. We hypothesized that low-vigor plants are less susceptible to drought either through the production of numerous xylem vessels (Trifilò et al 2007), or through the reduction in vessel diameter. Moreover, we predicted that these characteristics would confer decreased cavitation vulnerability during a period of soil water limitation.…”