ROLE OF ARBUSCULAR MYCORRHIZAL FUNGI IN UPTAKE OF PHOSPHORUS AND NITROGEN FROM SOIL

Colonization of plant roots by arbuscular mycorrhizal fungi can greatl y increase the plant uptake of phosphorus and nitrogen. The most promi nent contribution of arbuscular mycorrhizal fungi to plant growth is d ue to uptake of nutrients by extraradical mycorrhizal hyphae. Quantifi cation of hyphal nutrient uptake has become possible by the use of soi l boxes with separated growing zones for roots and hyphae. Many (but n ot all) tested fungal isolates increased phosphorus and nitrogen uptak e of the plant by absorbing phosphate, ammonium, and nitrate from soil . However, compared with the nutrient demand of the plant for growth, the contribution of arbuscular mycorrhizal fungi to plant phosphorus u ptake is usually much larger than the contribution to plant nitrogen u ptake. The utilization of soil nutrients may depend more on efficient uptake of phosphate, nitrate, and ammonium from the soil solution even at low supply concentrations than on mobilization processes in the hy phosphere. In contrast to ectomycorrhizal fungi, nonsoluble nutrient s ources in soil are used only to a limited extent by hyphae of arbuscul ar mycorrhizal fungi. Side effects of mycorrhizal colonization on, for example, plant health or root activity may also influence plant nutri ent uptake.