Quantitative Analysis of Vasculature in the Leaves of Festuca arundinacea (Poaceae): Implications for Axial Water Transport

Abstract

Morphology, xylem anatomy, and axial hydraulic conductivity were studied in mature leaves of Festuca arundinacea Schreb. to characterize the hydraulic architecture of a grass leaf. The axial hydraulic conductivity (Kh) was measured on leaf segments taken throughout the blades and compared with the theoretical axial hydraulic conductivity (Kt) computed from the measurement of the number of xylem elements and their diameters. Kt was correlated with Kh, but Kh was only 26% of Kt. Vessel length distributions were calculated from measurement of latex casts made by perfusing latex particles into xylem conduits. The longest vessels were 30 mm long, but the normal length was 13 and 9 mm in the sheath and the lamina, respectively. Kt was computed on a second batch of plants and was multiplied ($$K^{*}_{\mathrm{t}\,}$$ ) by an impediment factor to account for the discrepancy between Kh and Kt. The increase in vessel diameter up the sheath resulted in an acropetal increase in $$K^{*}_{\mathrm{t}\,}$$ . In the blade, a decrease in both vessel number and diameter resulted in an acropetal decrease in $$K^{*}_{\mathrm{t}\,}$$ . In the blade, $$K^{*}_{\mathrm{t}\,}$$ varied with the leaf area to be supplied, leading to a fairly constant leaf‐specific hydraulic conductivity over the length of the blade ($$K^{*}_{\mathrm{t}\,}$$ /distal leaf area). The blade joint possessed heterogeneous vessels, characterized by helical thickened elements, that were symmetrically flanked with pitted elements. The helical thickening in the blade joint averaged $$4.3\pm 0.8$$ mm in length and was associated with a reduction in vessel diameter of 29%, resulting in a local reduction of $$K^{*}_{\mathrm{t}\,}$$ of 75%. The implications of this hydraulic architecture on the water relations of grass leaves is discussed