Is nitrogen uptake after anthesis in wheat regulated by sink size?

Increased grain yield and protein content are two important goals in wheat production. To increase yield potential, the recent approach in winter wheat breeding in China is to breed genotypes with more large kernels per spike. However, the regulation of grain nitrogen accumulation in relation to spike size is overlooked. This study was performed to investigate the effect of post-anthesis N uptake on grain N accumulation, and its regulation by N fertilization in two wheat cultivars with different spike sizes. The results showed that the cultivar LZ953, with large spikes and numerous kernels, also had high potential for N uptake after anthesis. Additional N application at anthesis could increase its post-anthesis N uptake and grain N content. In contrast, LM14, a cultivar with small spikes, showed low N uptake after anthesis, and additional N at anthesis had little effect on its post-anthesis N uptake. When the large sink size of LZ953 was reduced by removing the upper one-third of the spike, post-anthesis N uptake was greatly reduced, indicating a feedback regulation of sink size on the post-anthesis N uptake. Data also showed that the rapid senescence of LM14 limited its capacity to take up more N after anthesis. Our results suggest that only cultivars with large spikes may benefit from the increased N application at the late grain-filling stage and increase the grain N accumulation. (C) 2000 Elsevier Science B.V. All rights reserved.