Partitioning and flows of ions and nutrients in salt‐treated plants ofLeptochloa fuscaL. Kunth

summary An empirically based modelling technique, based on the relative immobility of Ca2+in phloem, was used quantitatively to describe uptake, flow in xylem and phloem, and partitioning of K+, Na+, Mg2+, and Cl−for a 13‐d period at the end of vegetative growth of the main shoot inLeptochloa fusca(L.) Kunth grown in presence of 100 mM NaCl. The model incorporated data on net increments of the ions in the root, the stem, individual leaf sheaths and laminae (blades), and tillers, secretion of salt by glandular hairs on sheaths and laminae, and the molar ion:Ca ratios in the xylem sap. Molar ratios of uptake of Na:Cl:K were 1.27: 1.12:1, indicating an uptake selectivity of 11.3 in favour of K+against Na+. The flow pattern of K+ in the main shoot featured relatively low permanent deposition (22% of the intake into the shoot in the stem axis and 10% in leaves) but a high return flow via phloem to the root (67%) followed by cycling of K+. In the whole plant a large share (72%) of K+uptake was utilized for growth of tillers but K+cycling from shoot to root amounted to 96% of uptake. The flow pattern of Na+featured a somewhat smaller commitment (62%) to deposition in tillers. In the main shoot 33% of Na+intake was deposited in the stem and 35% in leaves. In these the sheaths incorporated by far the larger (2.8‐fold) share compared with the laminae. Of the total Na1intake, 9%, was excreted by salt glands (3.3‐fold more by laminae than sheaths) and only 31% was translocated to the root via phloem. Flows and partitioning of Cr were similar to those of Na+, but phloem transport was larger (60% of intake into the main shoot) than that of Na+. The flow patterns are discussed in relation to changes in ion concentrations of leaves with leafage and in relation to salinity tolerance. It is suggested that besides salt secretion a high efficiency in K+utilization contributes to the performance of this halophyte in presence of salt