Hydraulic resistance components of mature apple trees on rootstocks of different vigours

Abstract

Dwarfing of fruit trees is often achieved through the use of dwarfing rootstocks. Dwarf trees are characterized by sustained reductions in vegetative growth during the lifetime of the tree. The dwarfing mechanism is not well understood, but it has been hypothesized that hydraulic properties of the rootstock and the graft union are involved. It is hypothesized here that leaf- or stem-specific resistance of at least one hydraulic component of the water transport system would be negatively correlated with rootstock 'vigour', and this could be useful for selection of rootstocks. Hydraulic resistance (R) of fully grown apple trees on a variety of rootstocks of different 'vigours' was measured. Most measurements were with the evaporative flux (EF) method, where water uptake measured with sap flow sensors was related to the pressure gradient from soil (taken as pre-dawn leaf) and midday root (taken as covered root-sucker), stem (from covered leaf), and exposed and shaded leaf water potentials (Psi(l)). R of trees on dwarfing M9 rootstock was compared with that of more vigorous MM106 and MM111 rootstocks in Israel and Vermont, USA. In Israel, M9 consistently had higher leaf-specific hydraulic resistance (R(l)) in the soil to scion stem pathway, but this difference was only significant for one summer. R was larger in M9 between the root and stem, implicating the graft union as the site of increased resistance. In Vermont, R(l) of 9- and 10-year-old trees on six rootstocks of various vigours was not consistently related to vigour, and stem-specific resistance (R(s)) increased with increasing vigour. High pressure flow meter (HPFM) measurements gave a lower R than the EF method in all but one case, perhaps indicating a significant amount of xylem dysfunction in these trees, and demonstrated the increased resistivity of stem sections that included dwarf graft unions as compared with non-graft stem sections. It is concluded that stem- and leaf-specific R are not consistently positively correlated with dwarfing, although the increased resistivity of the graft union in dwarfing rootstocks may influence the transport of water and other elements across the graft union, and therefore be involved in the dwarfing mechanism.

Analysis of Hydraulic Conductance Components in Field Grown, Mature Sweet Cherry Trees

“…These are important evidences that allow us to state that the hysteresis detected is of marginal relevance. Indeed, the occurrence of a statistically significant linear relationship between E and Ψ has been considered elsewhere as an indication of a negligible capacitance effect in several fruit trees (Elfving et al, 1972;Cohen et al, 1983;Naor and Wample, 1994;Steinberg et al, 1990;Alarcón et al, 2003;Tognetti et al, 2004;Cohen et al, 2007). Also, for each day separately, E variations resulted in proportional changes in ΨEC, showing that conductances remained constant on a diurnal basis.…”

“…Several studies have described a direct relationship between whole plant hydraulic conductance and stomatal conductance, water use, and gas exchange (Hubbard et al, 2001;Schultz, 2003;Tyree, 2003;Cohen et al, 2007), therefore affecting plant transpiration and the plant potential for biomass accumulation. Also, rootstockinduced vigor control has been hypothetically related to lower K of certain rootstocks (Atkinson and Else, 2001;Basile et al, 2003;Olmstead et al, 2006;Cohen et al, 2007). While some studies state that roots exhibit the lower conductances in fruit trees such as apple (Malus domestica Borkh.)…”

Alterações anatômicas do sistema vascular em porta-enxertos de videira

“…Outros estudos também apontam a diferença de crescimento vegetativo como característica relacionada ao vigor dos porta-enxertos em macieiras (Cohen et al, 2007) e cerejeiras (Gonçalves et al, 2007).…”

“…Estas características do tecido xilemático podem estar relacionadas à maior ou menor resistência hidráulica da planta e às características dos elementos de vaso do xilema (Olmstead, 2006;Wu et al, 2011). Outros trabalhos também têm mostrado a formação das estruturas do sistema vascular em relação ao vigor dos porta-enxertos (Cohen et al, 2007;Gonçalves et al, 2007). A condutividade hidráulica do xilema é um dos fatores relacionados ao vigor Tombesi et al, 2010), pois, a capacidade de uma planta de absorver e transportar água e nutrientes também depende das estruturas anatômicas (Wu et al, 2011;Lucas et al, 2013).…”

“…(1) . (Cohen et al, 2007;Brodersen et al, 2010), quando se consideram as condições de demanda por evapotranspiração, abertura estomática e diferença de pressão ou potencial hídrico. Com os resultados, pode-se inferir que os porta-enxertos de videira mais vigorosos apresentam maior área de xilema e maior diâmetro dos elementos de vaso, ou seja, proporcionam modificações de estrutura anatômica que podem resultar em maior potencial de condutividade hidráulica, conforme verificado em outras espécies (Olmstead et al, 2006;Tombesi et al, 2010).…”