Tracheid

About: Tracheid is a research topic. Over the lifetime, 1543 publications have been published within this topic receiving 43086 citations.

Xylem Structure and the Ascent of Sap

Abstract: 1 Conducting Units: Tracheids and Vessels.- 2 The Vessel Network in the Stem.- 3 The Cohesion-Tension Theory of Sap Ascent.- 4 Xylem Dysfunction: When Cohesion Breaks Down.- 5 Hydraulic Architecture of Woody Shoots.- 6 Hydraulic Architecture of Whole Plants and Plant Performance.- 7 Other Functional Adaptations.- 8 Failure and "Senescence" of Xylem Function.- 9 Pathology of the Xylem.- References.

Xylem Embolism in Ring-Porous, Diffuse-Porous, and Coniferous Trees of Northern Utah and Interior Alaska

Abstract: Xylem embolism was measured in nine tree species for one or more years. Species were ring-porous (Quercus sp.), diffuse-porous (Alnus, Betula, Populus spp.) or coniferous (Picea, Larix, Abies spp.). Intraspecific (Populus tremuloides) and intrageneric (Betula, Alnus) comparisons were made between sites in northern Utah and interior Alaska. Most embolism, >90% in some dicot species, occurred in winter. Within sites, dicot trees embolized more than conifers. Between sites, Alaskan dicot trees embolized less than their Utah counterparts. Differences were explained by vulnerability to embolism caused by freeze-thaw cycles. Most conifers were entirely resistant, whereas dicot trees were vulner- able. Less embolism in Alaskan dicot trees was associated with fewer freeze-thaw events in Alaska vs. Utah. Vulnerability was positively correlated with conduit volume and hy- draulic conductance per unit xylem area (ks). Tracheids were superior to vessels in avoiding freeze-thaw-induced embolism, and had lower k,. At the other extreme, ring-porous xylem had the highest k, but lost > 90% of hydraulic conductance after a single freeze-thaw event. Vulnerability to water-stress-induced cavitation was not correlated with conduit volume or k,. Dicot species either reversed winter embolism by refilling vessels with positive root pressures during spring (Betula, Alnus spp.), or tolerated it and relied on new xylem pro- duction to restore hydraulic conductance (Quercus sp.). Conifers reversed embolism by refilling tracheids in the absence of positive pressure. Populus species behaved inconsis- tently, showing some reversal one year but none the next. Even without embolism reversal, Populus species had hydraulic conductances per unit leaf area equal to other diffuse-porous species.

Size and function in conifer tracheids and angiosperm vessels

Abstract: The wide size range of conifer tracheids and angiosperm vessels has important consequences for function. In both conduit types, bigger is better for conducting efficiency. The gain in efficiency with size is maximized by the control of conduit shape, which balances end-wall and lumen resistances. Although vessels are an order of magnitude longer than tracheids of the same diameter, they are not necessarily more efficient because they lack the low end-wall resistance of tracheids with torus-margo pits. Instead, vessels gain conducting efficiency over tracheids by achieving wider maximum diameters. End-walls contributed 56-64% to total xylem resistance in both conduit types, indicating that length limits conducting efficiency. Tracheid dimensions may be more limited by unicellularity and the need to supply strength to homoxylous wood than by the need to protect against cavitation. In contrast, the greater size of the multicellular vessel is facilitated by fibers that strengthen heteroxylous wood. Vessel dimensions may be most limited by the need to restrict intervessel pitting and cavitation by air-seeding. Stressful habitats that promote narrow vessels should favor coexistence of conifers and angiosperms. The evolution of vessels in angiosperm wood may have required early angiosperms to survive a phase of mechanic and hydraulic instability.

Structure and function of bordered pits: new discoveries and impacts on whole-plant hydraulic function

Abstract: Bordered pits are cavities in the lignified cell walls of xylem conduits (vessels and tracheids) that are essential components in the water-transport system of higher plants. The pit membrane, which lies in the center of each pit, allows water to pass between xylem conduits but limits the spread of embolism and vascular pathogens in the xylem. Averaged across a wide range of species, pits account for > 50% of total xylem hydraulic resistance, indicating that they are an important factor in the overall hydraulic efficiency of plants. The structure of pits varies dramatically across species, with large differences evident in the porosity and thickness of pit membranes. Because greater porosity reduces hydraulic resistance but increases vulnerability to embolism, differences in pit structure are expected to correlate with trade-offs between efficiency and safety of water transport. However, trade-offs in hydraulic function are influenced both by pit-level differences in structure (e.g. average porosity of pit membranes) and by tissue-level changes in conduit allometry (average length, diameter) and the total surface area of pit membranes that connects vessels. In this review we address the impact of variation in pit structure on water transport in plants from the level of individual pits to the whole plant.

Evolution of Water Transport and Xylem Structure

Abstract: Land plants need water to replace the evaporation that occurs while atmospheric CO2 is diffusing into photosynthetic tissue. The water‐for‐carbon exchange rate is poor, and evolutionary history indicates a progression of innovations for cheap water transport—beginning in order with capillary suction at cell walls, stomatal regulation, hydroids, tracheids, secondary xylem, endodermis, and vessels. The radiation of plants in the Silurian and Devonian occurred when the need for water was at an all‐time low because of high CO2 concentration. Transport improvements appeared as water demand increased and CO2 dropped to current values in the Carboniferous and Permian. Stomatal regulation and high‐conductivity conduits permitted larger plants and a transition from poikilohydric to homoiohydric water relations. The evolution of conduits from hydroids through tracheids to vessels reflects the need to balance resistance to implosion and cavitation versus maximum hydraulic conductance and minimum conduit investment. ...