Is crop N demand more closely related to dry matter accumulation or leaf area expansion during vegetative growth?
ABSTRACT The 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.
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ABSTRACT: Partitioning of nitrogen among species was determined in a stand of a tall herbaceous community. Total amount of nitrogen in the aboveground biomass was 261 mmol N m–2, of which 92% was in three dominant species (Phragmites, Calamagrostis and Carex) and the rest was in the other eight subordinate species. Higher nitrogen concentrations per unit leaf area (n L) with increasing photosynthetically active photon flux density (PPFD) were observed in all species except for three short species. The changes in n L within species were mainly explained by the different nitrogen concentrations per unit leaf mass, while the differences in n L between species were explained by the different SLM (leaf mass per unit leaf area). Photon absorption per unit leaf nitrogen ( N ) was determined for each species. If photosynthetic activity was proportional to photon absorption, N should indicate in situ PNUE (photosynthetic nitrogen use efficiency). High N of Calamagrostis (dominant) resulted from high photon absorption per unit leaf area ( area ), whereas high N of Scutellaria (subordinate) resulted from low n L although its area was low. Species with cylinder-like leaves (Juncus and Equisetum) had low N , which resulted from their high n L. Light-saturated CO2 exchange rates per unit leaf area (CER) and per unit leaf nitrogen (potential PNUE) were determined in seven species. Species with high CER and high n L (Phragmites, Carex and Juncus) had low potential PNUE, while species with low CER and low n L showed high potential PNUE. NUE (ratio of dry mass production to nitrogen uptake) was approximated as a reciprocal of plant nitrogen concentration. In most species, three measures of nitrogen use efficiency (NUE, N and potential PNUE) showed strong conformity. Nitrogen use efficiency was high in Calamagrostis and Scutellaria, intermediate in Phragmites and relatively low in Carex. Nitrogen use efficiency of subordinate species was as high as or even higher than that of dominant species, which suggests that growth is co-limited by light and nitrogen in the subordinate species.Oecologia 01/1994; 100(3):203-212. · 3.01 Impact Factor
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ABSTRACT: This paper quantifies the effects of N-stress on development and growth of sorghum by identifying critical values for stover N% (SNC) and specific leaf nitrogen (SLN) for a range of physiological processes (rates of leaf appearance, leaf expansion, leaf area increase, and biomass accumulation). It also compares the merits of the SNC and SLN approach for implementation in the N-routines of crop growth simulation models. Data from experiments covering a range of nitrogen treatments, grown at three contrasting locations in Australia, were used in the analyses. For the rate of biomass accumulation, the critical and minimum SLN were constant for most of the growing season, except for early stages prior to approximately panicle initiation. For SNC, however, the critical and minimum values continued to decline throughout the growing season, although the decline was limited at later development stages. During the stage of leaf growth, the critical N content was similar for all processes considered. Although critical SLN was less sensitive to development stage than SNC, identification of a critical SLN was hampered if environmental effects on specific leaf area were present. The merit of each approach in simulation models will depend upon their ability to capture genotypic differences in N-dynamics. (C) 2001 Elsevier Science B.V. All rights reserved.01/2001;
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ABSTRACT: Several controlled environmental and field experiments were carried out to define the critical nitrogen dilution curve for winter oilseed rape, cultivar Goeland. This curve is described by the following power equation:N=4.48 W-0.25,whereNis the total nitrogen concentration in the shoot biomass andWthe shoot biomass. This curve has been validated over the range of shoot dry matter of 0.88 to 6.3 t ha-1. For lower shoot biomasses this equation overestimated the critical nitrogen concentration; we propose a constant value of 4.63 (Nis expressed in reduced N, which is a more stable N fraction in the shoot at these stages of development). These results have been validated in several pedoclimatic conditions in France on a single variety in 1994 and 1995. The higher position of this curve relative to the C3species reference curve (Greenwoodet al.,Annals of Botany67: 181–190, 1990) can be explained by the experimental conditions obtained by Greenwoodet al. (1990); therefore, all their rape data are rather close to the critical curve that we propose. The differences found between wheat and winter oilseed rape critical N dilution curves correspond to their respective leaf:stem dry matter ratio and the specific leaf loss phenomenon occuring in rape. Winter oilseed rape has a higher capacity of N accumulation in its shoot than wheat for the same aerial dry matter. The proportion of nitrate in shoots rises with the nitrogen nutrition index (N.N.I.) and is more important for rapeseed than for wheat for the same N.N.I. This difference is especially high at the beginning of flowering when the shade provided by the canopy of rapeseed flowers decreases nitrate reductase activity.Annals of Botany - ANN BOT. 01/1998; 81(2):311-317.