Intra-specific trends of lumen and wall resistivities of vessels within the stem xylem vary among three woody plants

Water flow through xylem vessels encounters hydraulic resistance when passing through the vessel lumen and end wall. Comparative studies have reported that lumen and end wall resistivities co-limit water flow through stem xylem in several angio-sperm woody species that have vessels of different average diameter and length. This study examined the intra-specific relationship between the lumen and end wall resistivities (R-lumen and R-wall) for vessels within the stem xylem using three deciduous angiosperm woody species found in temperate forest. Morus australis Poir. and Acer rufinerve Siebold et Zucc. are early-and late-successional species, and Vitis coignetiae Pulliat ex Planch is a woody liana. According to the Hagen-Poiseuille equation, R-lumen is proportional to the fourth power of vessel diameter (D), whereas vessel length (L) and inter-vessel pit area (A(pit)) determine R-wall. To estimate R-lumen and R-wall, the scaling relationships between the L and D and between A(pit) and D were measured. The scaling exponents between L and D were 1.47, 3.19 and 2.86 for A. rufinerve, M. australis and V. coignetiae, respectively, whereas those between A(pit) and D were 0.242, 2.11 and 2.68, respectively. Unlike the inter-specific relationships, the wall resistivity fraction (R-wall/(R-lumen + R-wall)) within xylem changed depending on D. In M. australis and V. coignetiae, this fraction decreased with increasing D, while in A. rufinerve, it increased with D. Vessels with a high wall resistivity fraction have high R-wall and total resistivity but are expected to have low susceptibility to xylem cavitation due to a small cumulative A(pit). In contrast, vessels with a low wall resistivity fraction have low R-wall and total resistivity but high susceptibility to xylem cavitation. Because the wall resistivity fraction varies with D, the stem xylem contains vessels with different hydraulic efficiencies and safety to xylem cavitation. These features produce differences in the hydraulic properties of plants with different life forms.