Characterization of two arbuscular mycorrhizal fungi in symbiosis with Allium porrum: colonization, plant growth and phosphate uptake

Two arbuscular mycorrhizal fungi, Scutellospora calospora and Glomus sp. 'C ity Beach', were grown in soil conditions suitable for colonization of Alli um porrum. Effects on plant growth and phosphate uptake were examined. Isol ates of S. calospora (including the one used here) have been shown by other s to vary in their stimulation of plant growth, and appear to be inefficien t in the transfer of P from the fungus to the host. Our hypothesis was that such isolates of S. calospora may be more aggressive colonizers than other fungi, thus preventing growth increases or producing strong growth depress ions in the host plant. In fact, inoculation with either fungus increased g rowth of plants in their respective soils both low in P (P-0) and with adde d P (P-1) by 42 d. The effect on growth due to mycorrhizal symbiosis (i.e. mycorrhizal growth response, % MGR) at 42 d was higher in plants grown in P , soil. Plants colonized by Glomus sp. 'City Beach' had a greater % MGR tha n plants colonized by S. calospora. Both fungi colonized plants to high lev els. The percentage of root length colonized was higher in P-0 soil than in P-1 soil at 21 d. The internal development of S. calospora appeared less a ffected by addition of P than Glomus sp. 'City Beach' at the early harvests . Formation of arbuscules followed the same trends as total colonization. S hoot P concentration was significantly higher in mycorrhizal plants than in non-mycorrhizal plants, by 21 d in P-1 soil and by 28 d in P-0 soil. Diffe rent percentage responses to added P based on total plant dry weight (% PGR ) were observed at 28 and 42 d between the plants colonized by the two fung i. The increased P content due to mycorrhizal colonization (% MPR) differed with soil P. For both fungi grown in their respective soils, the response was greater in plants grown in P-0 soil. Although the isolate of S. calospo ra used is an aggressive arbuscular mycorrhizal fungus with some hosts, it promotes a strong positive plant growth response in A. porrum after a mild initial growth depression.