Root age and phosphorus effects on colonization of Andropogon gerardii by mycorrhizal fungi

We examined the effects of plant age and root age on mycorrhizal colonization in the obligate mycotrophic grass Andropogon gerardii grown at high and low rates of soil phosphorus availability. There were significant interactions between soil P availability, plant age, root age and mycorrhizal colonization. Mycorrhizal colonization of 1-week-old roots increased with plant age, but was not significantly affected by soil P availability. Colonization of roots increased significantly with increasing root age only in the low-P treatment. Although the high-P treatment increased rates of root extension for some root age classes, there were not consistently lower rates of colonization in these roots. Studies of P acquisition by A. gerardii and other mycotrophic plants should take these interacting factors into account, especially when examining exploitation of nutrient-enriched patches.