02870naa a2200205 a 450000100080000000500110000800800410001910000110006024501180007126000090018950000200019852022630021865300250248165300220250665300080252865300200253665300130255665300270256977300680259610777432011-06-29       2007    bl uuuu     u00u1 u    #d1 aEpagri  aIs crop N demand more closely related to dry matter accumulation or leaf area expansion during vegetative growth?  c2007  aISSN, 0378-4290  aThe critical crop nitrogen uptake is defined as the minimum nitrogen uptake necessary to achieve maximum biomass accumulation (W). Across a range of crops, the critical N uptake is related to W by a power function with a coefficient less than unity that suggests crop N uptake is co-regulated by both soil N supply and biomass accumulation. However, crop N demand is also often linearly related to the expansion of the leaf area index (LAI) during the vegetative growth period. This suggests that crop N demand could be also linked with LAI extension. In this paper, we develop theory to combine these two concepts within a common framework. The aim of this paper is to determine whether generic relationships between N uptake, biomass accumulation, and LAI expansion could be identified that would be robust across both species and environment types. To that end, we used the framework to analyze data on a range of species, including C3 and C4 ones and mono- and di-cotyledonous crops. All crops were grown in either temperate or tropical and subtropical environments without limitations on N supply. The relationship between N uptake and biomass was more robust, across environment types, than the relationship of LAI with biomass. In general, C3 species had a higher N uptake per unit biomass than C4 species, whereas dicotyledonous species tended to have higher LAI per unit biomass than monocotyledonous ones. Species differences in N uptake per unit biomass were partly associated with differences in LAI and N-partitioning. Consequently the critical leaf-N uptake per unit LAI (specific leaf nitrogen, SLN) was relatively constant across species at 1.8?2.0 g m−2, a value that was close to published data on the critical SLN of new leaves at the top of the canopy. Our results indicate that critical N uptake curves as a function of biomass accumulation may provide a robust platform for simulating N uptake of a species. However, if crop simulation models are to capture the genotypic and environmental control of crop N dynamics in a physiologically functional manner, plant growth has to be considered as the sum of a metabolic (e.g. leaves) and a structural (e.g. stems) compartment, each with its own demand for metabolic and structural N.  aBiomass accumulation  aCritical N-uptake  aLAI  aLeaf Area Ratio  aN-demand  aSpecific Leaf Nitrogen  tField Crops Research, Amsterdamgv. 100, n. 1, p. 91-106, 2007.