EFFECT OF WATER-STRESS ON PHOSPHORUS UPTAKE BY MYCORRHIZAS OF PINUS-RADIATA

The uptake of 32P by excised non‐mycorrhizal and mycorrhizal roots of Pinus radiata was examined in solutions adjusted with polyethylene glycol 4000 to water potentials of 0, 005, 01, 0.3, 0.6 and 1.2 negative MPa. Solutions contained 5 μm KH2PO4 and 0.5 mM CaSO4. Uptake of phosphate was little affected by water potential in either mycorrhizal or non‐mycorrhizal roots. Changes in water potential also caused no appreciable change in its efflux from mycorrhizal roots, suggesting little effect on permeability to phosphate. Uptake of phosphate, when based on surface area of the roots, was similar for both mycorrhizal and non‐mycorrhizal roots, but was less for non‐mycorrhizal roots when based on fresh wt. It is thus considered that changes in soil water potential per se may have little impact on absorption processes by mycorrhizal and non‐mycorrhizal roots. However, effective penetration of soil by mycelial strands and hyphae from ectomycorrhizas may be important in offsetting lowered transfer of ions to roots under low soil moisture conditions. Copyright © 1979, Wiley Blackwell. All rights reserved