How are leaves plumbed inside a branch? Differences in leaf-to-leaf hydraulic sectoriality among six temperate tree species

Abstract

The transport of water, sugar, and nutrients in trees is restricted to specific vascular pathways, and thus organs may be relatively isolated from one another (i.e. sectored). Strongly sectored leaf-to-leaf pathways have been shown for the transport of sugar and signal molecules within a shoot, but not previously for water transport. The hydraulic sectoriality of leaf-to-leaf pathways was determined for current year shoots of six temperate deciduous tree species (three ring-porous: Castanea dentata, Fraxinus americana, and Quercus rubra, and three diffuse-porous: Acer saccharum, Betula papyrifera, and Liriodendron tulipifera). Hydraulic sectoriality was determined using dye staining and a hydraulic method. In the dye method, leaf blades were removed and dye was forced into the most proximal petiole. For each petiole the vascular traces that were shared with the proximal petiole were counted. For other shoots, measurements were made of the leaf-area-specific hydraulic conductivity for the leaf-toleaf pathways (k LL ). In five out of the six species, patterns of sectoriality reflected phyllotaxy; both the sharing of vascular bundles between leaves and k LL were higher for orthostichous than non-orthostichous leaf pairs. For each species, leaf-to-leaf sectoriality was determined as the proportional differences between non-orthostichous versus orthostichous leaf pairs in their staining of shared vascular bundles and in their k LL ; for the six species these two indices of sectoriality were strongly correlated (R 2 50.94; P <0.002). Species varied 8-fold in their k LL -based sectoriality, and ringporous species were more sectored than diffuseporous species. Differential leaf-to-leaf sectoriality has implications for species-specific co-ordination of leaf gas exchange and water relations within a branch, especially during fluctuations in irradiance and water and nutrient availability.

Ice Propagation in Dehardened Alpine Plant Species Studied by Infrared Differential Thermal Analysis (IDTA)

“…Leaf and branch junctions are known as potential water flow constrictions and segmentation points in the hydraulic architecture (Schulte and Brooks, 2003). The sectoriality of the vascular system describes the degree of hydraulic coupling between plant parts, which may range from full coupling to limited interconnectedness (Brooks et al, 2003;Schulte and Brooks, 2003;Orians et al, 2005;Ellmore et al, 2006;Zanne et al, 2006). Hydraulic sectoriality may explain the freezing pattern in S. acaulis with its highly branched shoot and S. incanus with leaves emerging from a compressed stem.…”

Vascular structure contributes to shoot sectoriality in Selaginella kraussiana

“…Dye loading experiments, although not directly showing xylem or phloem transport, are treated as a reliable method to visualize the structure and functionality of vascular connections [30][31][32]. This method was successfully used, e.g., to show the sympodial network in the primary vascular system of clonal species [32] and the continuity of particular vessels in trees (e.g., [33][34][35]). In our case, dye spreading has established the sectoriality of the shoot and the developmentally regulated independence of the vascular strands.…”

Plant Volatile Signalling: Multitrophic Interactions in the Headspace

“…81 Vascular connectivity is high in orthostichous leaves, intermediate in adjacent leaves and absent in opposite leaves. 82,83 Moreover, vascular connections are absent between branches in shrubs with long branches emanating from a basal crown. 84 Thus, vascular signals elicit patchy defences in neighbouring leaves and branches.…”

“…87 Volatiles also facilitate signal transfer between tomato leaves. When air contact is eliminated, only leaves with direct vascular connections to the damaged leaf show significant changes in defence chemistry, 82 suggesting that volatiles mediate the interaction. Similarly, volatiles have been shown to elicit defence compound production in neighbouring branches of cottonwood, 88 sagebrush 89 and blueberry plants 84 with long, distal branches and limited vascular connectivity.…”