N uptake and distribution in crops: an agronomical and ecophysiological perspective.
The rate of N uptake of crops is highly variable during crop development and between years and sites. However, under ample soil N availability, crop N accumulation is highly related to crop growth rate and to biomass accumulation. Critical N concentration has been defined as the minimum N concentration which allows maximum growth rate. Critical N concentration declines during crop growth. The relationship between critical N concentration and biomass accumulation over the growth period of a crop is broadly similar within major C(3) and C(4) cultivated species. Therefore, the critical N concentration concept is widely used in agronomy as the basis of the diagnosis of crop N status, and allows discrimination between situations of sub-optimal and supra-optimal N supply. The relationship between N and biomass accumulation in crops, relies on the interregulation of multiple crop physiological processes. Among these processes, N uptake, crop C assimilation and thus growth rate, and C and N allocation between organs and between plants, play a particular role. Under sub-optimal N supply, N uptake of the crop depends on soil mineral N availability and distribution, and on root distribution. Under ample N supply, N uptake largely depends on growth rate via internal plant regulation. Carbon assimilation of the crop is related to crop N through the distribution of N between mature leaves with consequences for leaf and canopy photosynthesis. However, although less commonly emphasized, carbon assimilation of the crop also depends on crop N through leaf area development. Therefore, crop growth rate fundamentally relies on the balance of N allocation between growing and mature leaves. Nitrogen uptake and distribution also depends on C allocation between organs and N composition of these organs. Within shoots, allocation of C to stems generally increases in relation to C allocation to the leaves over the crop growth period. Allocation of C and N between shoots and roots also changes to a large extent in relation to soil N and/or crop N. These alterations in C and N allocation between plant organs have implications, together with soil availability and carbon assimilation, on N uptake and distribution in crops. Therefore, N uptake and distribution in plants and crops involves many aspects of growth and development. Regulation of nitrogen assimilation needs to be considered in the context of these interregulatory processes.
Gastal
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Unité d'Ecophysiologie des Plantes Fourragères, INRA-UEPF, 86600 Lusignan, France. gastal@lusignan.inra.fr
Lemaire
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D000383:Agriculture; D018533:Biomass; D002244:Carbon / Q000378:metabolism; D018556:Crops, Agricultural / Q000187:drug effects / Q000502:physiology*; D004463:Ecology; D008027:Light; D009584:Nitrogen / Q000378:metabolism* / Q000494:pharmacology; D010788:Photosynthesis / Q000187:drug effects / Q000502:physiology*; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology; D018517:Plant Roots / Q000187:drug effects / Q000502:physiology; D018547:Plant Stems / Q000187:drug effects / Q000502:physiology; D010944:Plants / Q000145:classification; D012987:Soil / Q000032:analysis; D013997:Time Factors
D012987:Soil; D002244:Carbon; D009584:Nitrogen