Root hydraulic conductivity and xylem sap levels of zeatin riboside and abscisic acid in ectomycorrhizal Douglas fir seedlings

Abstract

Mechanistic hypotheses to explain mycorrhizal enhancement of root hydraulic conductivity (L_p) suggest that phosphorus (P) nutrition, plant growth substances and/or altered morphology may be responsible. Such ideas are based on work with VA (vesicular-arbuscular) mycorrhizas. Since VA mycorrhizas and ectomycorrhizas differ in many respects, they may alter host plant water uptake via different mechanisms. This paper examines L_p in various ectomycorrhizal associations while considering factors which are important to the VA mycorrhizal effect on L_p. Douglas fir Pseudotsuga menziesii (Mirb.) France] seedlings inoculated with the ectomycorrhizal fungi Laccaria bicolor (Maire) Orton and Hebeloma crustuliniforme (Bull. ex St. Amans) Quel. and non-inoculated seedlings infected naturally with Thelephora were grown under three low levels of P fertilization (1, 10 and 1OO µM P). Seedling morphology, tissue P levels, L_p and plant growth substance levels in xylem sap were measured after nine months growth. Increased tissue P and decreased root/shoot ratio correlated with increased L_p in each of the mycorrhizal treatments. When adjusted for the effect of these two factors, L_p of Laccaria and Hebeloma seedlings was still lower than the Thelephora seedlings. In a subsequent experiment, the L_p of seedlings with Hebeloma and Rhizopogon vinicolor Smith mycorrhizas was compared to the L_p of non-mycorrhizal seedlings,(grown at 100 µM P)and no differences were found among treatments. The lack of an ectomycorrhizal effect on L_p is quite different from the enhancement of host L_p by VA mycorrhizas. Zeatin riboside concentrations of Thelephora- and Hebeloma-infected seedlings were similar, yet higher than with Laccaria. There was no relationship between plant growth substances and L_p in ectomycorrhizal Douglas fir, despite lower zeatin riboside concentrations for Laccaria-inoculated plants.

Citation

Coleman, Mark D.; Bledsoe, Caroline S.; Smit, Barbara A. 1990. Root hydraulic conductivity and xylem sap levels of zeatin riboside and abscisic acid in ectomycorrhizal Douglas fir seedlings. New Phytol. (1990). 115, 275-284