Role of Mineral Nutrients in Photosynthesis and Yield Formation
İsmail Çakmak, Christof Engels
Abstract
The capacity of plants to assimilate carbon in the source organs and translocate and utilize photosynthates in the sink organs determines growth rate and productivity of crop plants. This capacity of crop plants is directly affected by several factors, such as water availability, light conditions, and mineral nutrients (Geiger, Koch, and Shieh, 1996). Mineral nutrients possess several roles in formation, partitioning, and utilization of photosynthates. Therefore, mineral nutrient deficiencies substantially impair production of dry matter and its partitioning between the plant organs (Marschner, Kirkby, and Cakmak, 1996; McDonald, Ericsson, and Larsson, 1996). Although total dry matter production is similarly affected by mineral nutrient deficiencies, partitioning of dry matter between plant organs (e.g., shoots and roots) is differentially influenced by different mineral nutrient deficiencies. In a study with bean plants, total dry matter production was similar under P (phosphorus), K (potassium), and Mg (magnesium) deficiencies. Under P deficiency, however, a greater proportion of dry matter was partitioned to roots, while under K and Mg deficiencies root growth was mark edly decreased (Cakmak, Hengeler, and Marschner, 1994a). These changes were paralleled with the corresponding changes in the distribution of carbohydrates between roots and shoots, indicating differential effects of mineral nutrients on partitioning of photosynthates within plants. Similarly, in birch seedlings, shoot and root growth was differently diminished by deficiency of several nutrients. Under deficiency of N (nitrogen), K, and S (sulfur), a large proportion of total dry matter was allocated to the roots, but under deficiencies of Mg. K, and Mn (manganese) dry matter partitioning toward the roots was depressed severely (Ericsson, 1995).