Background: It is known that hexaploid common wheat (Triticum aestivum L.) has stronger adaptability to many stressful environments than its tetraploid wheat progenitor. However, the physiological basis and evolutionary course to acquire these enhanced adaptabilities by common wheat remain understudied. Here, we aimed to investigate whether and by what means tolerance to low-nitrogen manifested by common wheat may emerge immediately following allohexaploidization. Results: We compared traits related to nitrogen (N) metabolism in a synthetic allohexaploid wheat (neo-6x, BBAADD) mimicking natural common wheat, together with its tetraploid (BBAA, 4x) and diploid (DD, 2x) parents. We found that, under low nitrogen condition, neo-6x maintained largely normal photosynthesis, higher shoot N accumulation, and better N assimilation than its 4x and 2x parents. We showed that multiple mechanisms underlie the enhanced tolerance to N-deficiency in neo-6x. At morphological level, neo-6x has higher root/shoot ratio of biomass than its parents, which might be an adaptive growth strategy as more roots feed less shoots with N, thereby enabling higher N accumulation in the shoots. At electrophysiological level, H+ efflux in neo-6x is higher than in its 4x parent. A stronger H+ efflux may enable a higher N uptake capacity of neo-6x. At gene expression level, neo-6x displayed markedly higher expression levels of critical genes involved in N uptake than both of its 4x and 2x parents. Conclusions: This study documents that allohexaploid wheat can attain immediate higher tolerance to N-deficiency compared with both of its 4x and 2x parents, and which was accomplished via multiple mechanisms.
