Phosphorus-32 absorption and translocation to host plants by arbuscular mycorrhizal fungi at low root-zone temperature

Arbuscular mycorrhizal (AM) mycelia persist in soil over winter. Functioning of the AM symbiosis very early in the spring when the soil temperature is low may be of ecological significance for perennial and biannual plants in cool climates. An indoor experiment was conducted to investigate the effects of low root-zone temperatures on P-32 uptake by 10-week-old leek plants (Allium porrum L.) inoculated or not with the AM fungus Glomus intraradices Schenck & Smith. Plants were grown in a greenhouse at approximately 23degreesC prior to exposing their roots to 23degreesC, 15degreesC or 0degreesC. Mycorrhizal colonization increased P-32 activity of leek leaves at a root-zone temperature of 23degreesC seven days after injection of P-32 into the soil, whereas 14 days after injection, P-32 increases were measured at both 23degreesC and 15degreesC. The lack of difference in 32P activity between AM and non-AM plants at 0degreesC, both 7 and 14 days after injection, suggests that the AM fungus is not functional at this low root-zone temperature.