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George E. 2000. Nutrient uptake, pp. 307-344. In: Arbuscular mycorrhizas: physiology and function. Eds: Y Kapulnick and DD Douds Jr. Kluwer Academic Press.
The colonization of plant roots by arbuscular mycorrhizal (AM) fungi can greatly affect the plant uptake of mineral nutrients. It may also protect plants from harmful elements in soil. The contribution of AM fungi to plant nutrient uptake is mainly due to the acquisition of nutrients by the extraradical mycorrhizal hyphae. The quantification of the potential of hyphae for nutrient uptake can conveniently be made in experiments with soils separated into growing zones for roots and hyphae. Many mycorrhizal fungi can transport nitrogen, phosphorus, zinc, and copper to the host plant, but other nutrients can also be taken up and translocated by the hyphae. Among the nutrients, phosphorus is often the key element for increased growth or fitness of mycorrhizal plants because phosphorus is transported in hyphae in large amounts compared to the plant phosphorus demand. In addition to the direct element uptake by hyphae, mycorrhizal colonization can also have effects on root morphology and physiology leading to indirect effects of colonization on nutrient uptake. To date, the evidence for distinct differences between nonmycorrhizal and mycorrhizal plants in the use of non-soluble nutrient sources in soil is contradictory. The understanding of physiological differences in element uptake between isolates of AM fungi remains largely descriptive. Moreover, a quantification of the actual contribution of mycorrhizal fungi to nutrient uptake of plants at different growth stages and under different environmental conditions is still difficult. Novel methodology, for example the use of stable isotopes or molecular tools, will help to focus research in the next decade on the role of mycorrhizal fungi in plant nutrient uptake under ecosystem conditions rather than in controlled experimental environments.
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