Arbuscular mycorrhiza and phosphorus as controlling factors in the life history of <i>Hyacinthoides non‐scripta</i> (L.) Chouard ex Rothm.

Abstract

summary This investigation aimed to assess the degree of dependence of young plants of Hyacinthoides non‐scripta (L.) Chouard ex Rothm. on the formation of arbuscular mycorrhiza (AM) at different stages of its life cycle. H. non‐scripta is a bulbous perennial with a restricted root system of coarse, unbranched elements which are plainly inadequate for the acquisition of phosphate (P) from soil. In a glasshouse experiment non‐mycorrhizal H. non‐scripta were unable to take up sufficient P to maintain a positive P budget, confirming that the species is obligately mycorrhizal when adult. We needed to be able to assess the ages of field‐collected plants. The bulb of H. non‐scripta , which is totally rebuilt annually, provides no indicator of age other than size. The development of individual bulbs was monitored in reconstructed soil profiles for several years and the relationship of size and age calculated in order to determine the age structure of a population in the field and to quantify the mycorrhizal colonization of their roots according to age and depth in the soil. Seedlings of H. non‐scripta are supplied with a P‐rich endosperm and initially inhabit upper soil horizons where P is plentiful. However, they are at risk from winter frosts, summer drought and, possibly, predators. During their first four to five seasons they descend in the soil to a depth of approximately 20 cm, down a gradient of decreasing soil phosphorus concentration; simultaneously, their roots become increasingly colonized by arbuscular mycorrhizal fungi. Because of the change in environment, they appear to become increasingly dependent on the symbiosis, suggesting that the association changes from facultative to obligate during the plant's life history.