Mycorrhizal Effects on Potassium Fluxes by Northwest Coniferous Seedlings

Abstract

In ectomycorrhizae, the relative abilities of mycobiont and host plant to take up and store inorganic nutrients are not easily determined due to the intimate physical relationship of the two components forming the association. Since [Bong.j Carr.) seedlings.Mycorrhizas significantly increased 8'Rb uptake rates while decreasing the amount of MRb released to the external solution. Using compartmental analysis, the flux data suggest that the primary mycorrhizal effects were to increase inward potassium fluxes across the fungal tonoplast and to decrease potassium efflux across the fungal tonoplast, as compared with nonmycorrhizal seedling roots. The result was greater potassium storage, presumably in the fungal vacuole. The three coniferous species responded differently to fungal infection with respect to potassium fluxes. Both cytoplasmic and vacuolar fluxes for mycorrhizal hemlock were 2-fold greater than for spruce and 3-fold greater than for Douglas fir. These results demonstrate the usefulness of compartmental analysis for study of ion fluxes in intact mycorrhizal root systems and suggest that the fungal tonoplast may be the site for regulation of potassium fluxes in these coniferous roots.Ectomycorrhizae increase uptake of many nutrients by plant roots (5,7,8,16,19). Harley and colleagues (6, 7) extensively studied P uptake by excised beech mycorrhizae and P storage in the fungus and its subsequent transfer to the host. Substantial storage of 32p occurred in the fungal sheath and only 10% of the absorbed P was transferred to the host core as inorganic P. These early pioneering studies relied on physical separation of fungus

Paxillus involutus Strains MAJ and NAU Mediate K+/Na+ Homeostasis in Ectomycorrhizal Populus × canescens under Sodium Chloride Stress

“…1). Rygiewicz and Bledsoe (1984) reported that external hyphae in EM symbiosis have a high capacity to take up K + and deliver the nutrient to the host plant. In addition to stimulating K + uptake, P. involutus colonization benefits the salinized hosts by slowing down the rate of K + loss.…”

Molecular and Functional Characterization of a Na+-K+ Transporter from the Trk Family in the Ectomycorrhizal Fungus Hebeloma cylindrosporum

“…Large amounts of K ϩ are, therefore, required for plant growth, and the availability of this cation is often limited in the absence of fertilization. In forest ecosystems, ectomycorrhizal symbiosis improves the whole mineral nutrition of the tree, including K ϩ nutrition (3,51). The fungal partner can explore large soil volumes and be very efficient in mobilizing and taking up K ϩ ions, which can thereafter be secreted toward the host plant.…”

Subcellular compartmentation of elements in non‐mycorrhizal and mycorrhizal roots of Pinus sylvestris: an X‐ray microanalytical study. II. The distribution of calcium, potassium and sodium

“…For example, George et al (1992), who examined the nutrient absorption by hyphae of Glomus mosseae found that this VA mycorrhizal fungus had no effect on K uptake. By contrast, Rygiewicz & Bledsoe (1984) found an enhanced K ()'Rb) uptake and storage in ectomycorrhizal roots due to higher uptake rates, an increase of vacuolar pool sizes and reduction of the K efflux.…”

“…These authors suggested that synthesis of organic acids by the fungi might be responsible for a higher availability of K in the soil. In conifers, the higher uptake of K by ectomycorrhizal associations has been attributed to increased influx rates, decreased efflux and an enhancement of the vacuolar pool (Rygiewicz & Bledsoe, 1984).…”