WATERLOGGING TOLERANCE OF ROOTS OF SITKA SPRUCE CLONES AND OF STRANDS FROM THELEPHORA-TERRESTRIS MYCORRHIZAS

Rooted cuttings of three clones of Sitka spruce (Picea sitchensis (Bong.) Carr.) were grown in 2 m tall transparent acrylic tubes of peat in insulated boxes out of doors. Roots of many of the trees formed mycorrhizas with Thelephora terrestris Ehrh.:Fr.; the extra-matrical mycelium and associated strands were visible in the tubes, together with the roots. Some of the tubes were waterlogged to submerge the lower part of the root and mycelial systems. Waterlogging was carried out in October, when roots were growing slowly, or in November, when growth had stopped. The fungal mycelium was growing on both occasions. The tubes were drained in the following March, and survival of main roots and fungus was measured to the point of regeneration. There were large differences between the two waterlogging treatments in root survival. October waterlogging caused substantial dieback, and roots survived to a mean depth of only 122 mm below the water table. November waterlogging resulted in little dieback, and survival depth was 308 mm. Differences between clones in root survival were statistically significant but small. The extra-matrical hyphae of T. terrestris died in both treatments, but all of the strand systems survived and regenerated in the following spring. Factors affecting survival are discussed, including growth and oxygen transport in roots and fungal strands.