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]）的升高促进了小麦的生长和产量，但通过降低籽粒中面筋浓度而影响籽粒蛋白质浓度（GP%），从而影响烘焙品质。二氧化碳对粮食质量产生负影响的原因仍在争论中。在CO2浓度升高的条件下，由于籽粒干重的增加高于氮吸收的增加，籽粒GP%的下降是生长稀释的结果。此外，还讨论了[CO2]升高可能会降低氮的吸收。籽粒氮素的最大来源是在开花前营养组织中积累的有机氮素的再动员。较小的一部分归因于氮素的转运，氮素在开花和籽粒成熟之间被同化。本研究将研究自由空气CO2富集（FACE）和3个水平的矿物氮（60-350 kg N ha-1）对氮素再动员和转运以及籽粒蛋白质浓度和组成的影响。通过叶片和茎的干重以及花期和籽粒成熟期氮素浓度的差异来量化氮素的再动员。在低氮供应条件下，由于茎部分的增加和叶片氮浓度的降低，升高的[CO2]是否会降低氮的再动员，这将被检验。花期施氮量的15N标记将用于研究CO2富集是否影响氮素转运，特别是在中等施氮水平下。我们将测试是否可以通过使用非常高水平的氮肥来防止CO2对GP%的降低。在所有这些实验中，将使用固体硝酸铵钙。在另一项试验中，植株只施用硝态氮，按常规水平施氮（180 kg hm -1）。本研究的目的是确定[CO2]升高对小麦氮素吸收、生长和GP%的影响是否受到N形态的强烈影响。除了植物生长测量外，还将记录环境条件，以便以后利用这些数据对气候变化下的植物生长和粮食质量进行建模。

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.