PRODUCTION AND NUTRITIONAL STRUCTURE OF CROPS: METABOLISM, CYCLING, AND SIGNALING

摘要

Crop production is highly dependent on nutrients and the acquisition of nutrients from soil, water, and air and is strongly related to the availability of nutrients. An insufficient uptake of nutrients reduces crop productivity. However, the production or growth of crops is not linearly related to the amount of nutrients available to plants for the following reasons: (1) The available plant nutrients are not always direct sources of plant production. Nitrate and carbon dioxide are the major N and C sources of green plants, but they must be transformed and metabolized into amino acids and organic acids, respectively, prior to usage for plant growth and production. (2) Unicellular bacteria can transform and metabolize nitrate and CO_2 into amino acidsand organic acids. In contrast, in the group of multi-cellular and multi-organ higher plants, to which most crops belong, there are divisions of metabolism among cells and among organs. Nitrate is only partly metabolized into amino acids in the root and, as a result, most of these amino acids and non-reduced nitrate are transported to the shoot. There, the nitrate is metabolized into amino acids, and the amino acids are further metabolized into other amino acids and used to synthesize high-molecular Ncompounds (nucleic acids and proteins).