Seasonal mycorrhizal colonization of winter wheat and its effect on wheat growth under dryland field conditions

A field experiment was conducted to deter mine the seasonal patterns of arb uscular mycorrhiza (AM) in a dryland winter wheat (Triticum aestivum L.) sy stem and to determine wheat growth and P uptake responses to inoculation wi th mycorrhizal fungus. Broadcast-incorporated treatments included (1) no in oculation with mycorrhizal fungus, with and without P fertilizer, and (2) m ycorrhizal fungal inoculation at a rate of 5000 spores of Glomus intraradic es (Schenck and Smith), per 30 cm in each row, with and without fertilizer P. Winter wheat was seeded within a day after treatments were imposed, and roots were sampled at five growth stages to quantify AM. Shoot samples were also taken for determination of dry matter, grain yield and yield componen ts, and N and P uptake. No AM infection was evident during the fall months following seeding, which was characterized by low soil temperature, while d uring the spring, the AM increased gradually. Increases in wheat grain yiel ds by enhanced AM were of similar magnitude to the response obtained from P fertilization. However, responses differed at intermediate growth stages. At the tillering stage, P uptake was mainly increased by P fertilization bu t not by fungal inoculation. At harvest, enhanced AM increased P uptake reg ardless of whether or not fertilizer P was added. The AM symbiosis increase d with rising soil temperatures in the spring, in time to enhance late-seas on P accumulation and grain production.