Bancal Pierre
INRA, UMR 1091 INRA/INAPG Environnement et Grandes Cultures, F-78850 Thiverval Grignon, France.
Ann Bot. 2009 Jun;103(8):1315-24. doi: 10.1093/aob/mcp077. Epub 2009 Apr 1.
Nitrogen (N) remobilization is the major source of N for grain filling in wheat, the other being N uptake after anthesis (N(up)); however, variations in remobilization efficiency are not fully understood. It is hard to tell whether the source or the sink effects predominate, because N in the culm at anthesis (N(ant)) correlates strongly with both N remobilization (N(rem)) and grain number (G(n)), respectively the main source and the main sink.
A pot experiment was thus designed to assess the relative contributions of the source and sink to N(rem) regulation. Using two cultivars of winter wheat (Triticum aestivum, 'Apache' and 'Autan'), three pre-anthesis and two post-anthesis N fertilization levels were applied in order to vary the N sources, while ear trimming at anthesis reduced sink size.
Unlike results observed at a scale of m(2), the equation binding N(ant) to N(rem) exhibited a negative intercept, challenging the concept of nitrogen remobilization efficiency. Before ear trimming, G(n) fitted well to N(ant), with a slope dependent on genotype. To obtain a sink variable that was less correlated with N(ant), the difference deltaG(n) was calculated between actual grain number and that which could be predicted from culm N before trimming. A multiple regression then predicted N(rem) (r(2) = 0.95) from N(ant), N(up) and deltaG(n), with fitting unbiased by fertilization treatment, trimming or genotype.
In untrimmed culms, deltaG(n) had a negligible effect, so that N(rem) could be fitted to N(ant) and N(up) only: grain N filling appeared to be determined by sources only (N(ant) and N(up)), not by sink, and the reduction of N(rem) by N(up) was quantified. In these 'normal' cases, the regulation of N(rem) should thus be located within the N sources themselves. In contrast, ear-trimming needs to be considered with caution as it introduced a sink limitation on N(rem); moreover one with an important genotype effect.
氮素再转运是小麦籽粒灌浆氮素的主要来源，另一个来源是开花后氮素吸收（N(up)）；然而，再转运效率的变化尚未完全明晰。很难判断是源效应还是库效应占主导，因为开花期茎秆中的氮素（N(ant)）分别与氮素再转运（N(rem)）和籽粒数量（G(n)）密切相关，而N(rem)和G(n)分别是主要的源和主要的库。
因此设计了一项盆栽试验，以评估源和库对N(rem)调控的相对贡献。使用两个冬小麦品种（普通小麦，‘Apache’和‘Autan’），设置了三个花前和两个花后施氮水平，以改变氮源，同时在开花期剪穗以减小库大小。
与在平方米尺度上观察到的结果不同，将N(ant)与N(rem)联系起来的方程呈现负截距，这对氮素再转运效率的概念提出了挑战。在剪穗前，G(n)与N(ant)拟合良好，斜率取决于基因型。为了获得一个与N(ant)相关性较小的库变量，计算了实际籽粒数量与剪穗前根据茎秆氮素预测的籽粒数量之间的差值deltaG(n)。然后通过多元回归从N(ant)、N(up)和deltaG(n)预测N(rem)（r(2)=0.95），拟合不受施肥处理、剪穗或基因型的影响。
在未剪穗的茎秆中，deltaG(n)的影响可忽略不计，因此N(rem)仅能与N(ant)和N(up)拟合：籽粒氮素灌浆似乎仅由源（N(ant)和N(up)）决定，而非由库决定，并且量化了N(up)对N(rem)的降低作用。在这些“正常”情况下，N(rem)的调控应位于氮源本身。相比之下，剪穗需要谨慎考虑，因为它对N(rem)引入了库限制；此外还有重要的基因型效应。
