Field studies on the interaction of mineral nitrogen supply and free air CO2 enrichment on grain protein content and grain protein composition of winter wheat

大气CO2浓度([CO2])的升高改善了小麦的生长和产量，但通过降低籽粒中的面筋含量从而影响小麦的烘焙品质，从而影响了籽粒中的蛋白质浓度(GP%)。二氧化碳对粮食品质产生负面影响的原因仍在争论中。讨论了在高CO_2浓度下，由于籽粒干重的增加大于氮素吸收的增加，导致GP%下降的原因是生长稀释。此外，还讨论了升高[CO2]可能会减少N的获取。籽粒氮素的最大量来自于营养组织中积累的有机氮的再动员，直到开花。一小部分归因于氮素的转运，氮素在开花和籽粒成熟期之间被同化。本研究将探讨利用自由空气二氧化碳浓度升高(FACE)和三种矿质氮素供应水平(60-350 kg N ha-1)对氮素再动员和运转以及对籽粒蛋白质含量和组成的影响。氮素的再动员将根据叶片和茎的干重以及开花期和籽粒成熟度之间的氮素浓度差异来量化。在低氮供应的情况下，升高的[CO2]是否会由于茎分数的增加和叶片氮浓度的降低而减少氮素的再动员。15N标记在开花时添加的氮肥将被用来研究二氧化碳的增加是否影响氮素的运转，特别是在中等氮肥水平下。我们将测试是否可以通过使用非常高的氮肥水平来防止二氧化碳导致的GP%的下降。在所有这些实验中，都将使用固体硝酸钙铵。在另一项试验中，植物将只使用硝态氮，施入通常水平的氮肥(180公斤ha-1)。本研究的目的是确定升高的[CO2]对小麦氮素吸收、生长和GP%的影响是否强烈地受N形态的影响。除了植物生长测量外，还将记录环境条件，以便以后使用这些数据来模拟气候变化下的植物生长和谷物质量。

The rise of the atmospheric CO2 concentration ([CO2]) improves wheat growth and yield but affects grain protein concentration (GP%) by decreasing gluten concentration in the grain and thus baking quality. The reasons for the negative CO2-effect on grain quality are still under debate. It is discussed that the decrease of GP% under elevated [CO2] results from growth dilution since the increase in grain dry weight is higher than the increase in N acquisition. Furthermore it is discussed that elevated [CO2] may reduce N acquisition. The largest amount for grain N comes from the remobilization of organic N accumulated in the vegetative tissue until anthesis. A smaller part is attributed to the translocation of N which is assimilated between anthesis and grain maturity. In this study the effects of elevated [CO2] using free air CO2 enrichment (FACE) and three levels of mineral nitrogen supply (60-350 kg N ha-1) on nitrogen remobilization and translocation and on concentration and composition of grain protein will be investigated. Remobilization of N will be quantified from the dry weights of the leaves and stems and the difference in N concentration between anthesis and grain maturity. It will be examined whether elevated [CO2] decreases N remobilization at low N supply due to an increase of the stem fraction and a decrease of the leaf N concentration. 15N labeling of the N fertilizer added at flowering will be used to investigate whether CO2 enrichment affects N translocation especially at medium level of N fertilization. We will test whether the decrease in GP% by CO2 can be prevented by using a very high level of N fertilization. In all these experiments solid calcium ammonium nitrate will be used. In an additional experiment plants will be supplied with a usual level of N fertilization (180 kg ha-1) by using only nitrate-N. The objective of this study is to determine whether the effect of elevated [CO2] on N uptake, growth and GP% of wheat is strongly influenced by the N-form. Beside plant growth measurements environmental conditions will be recorded enabling the later use of the data for modelling plant growth and grain quality under climate change.