Distinct Carbon and Nitrogen Metabolism of Two Contrasting Poplar Species in Response to Different N Supply Levels.

Poplars have evolved various strategies to optimize acclimation responses to environmental conditions. However, how poplars balance growth and nitrogen deficiency remains to be elucidated. In the present study, changes in root development, carbon and nitrogen physiology, and the transcript abundance of associated genes were investigated in slow-growing Populus simonii (Ps) and fast-growing Populus euramericana (Pe) saplings treated with low, medium, and high nitrogen supply. The slow-growing Ps showed a flourishing system, higher delta N-15, accelerated C export, lower N uptake and assimilation, and less sensitive transcriptional regulation in response to low N supply. The slow-growing Ps also had greater resistance to N deficiency due to the transport of photosynthate to the roots and the stimulation of root development, which allows survival. To support its rapid metabolism and growth, compared with the slow-growing Ps, the fast-growing Pe showed greater root development, C/N uptake and assimilation capacity, and more responsive transcriptional regulation with greater N supply. These data suggest that poplars can differentially manage C/N metabolism and photosynthate allocation under different N supply conditions.