Growth performance, photosynthesis, and root characteristics are associated with nitrogen use efficiency in six poplar species

Abstract Nitrogen (N) is one of the most important elements for plant growth and development. To reveal the interspecific variations of poplar species in response to changes in N levels and the essential traits that are closely linked to nitrogen use efficiency (NUE), six poplar species were subjected to 0.25, 2.5 or 7.5 mM NH 4 NO 3 . The morphological and physiological traits were analyzed, and the effects of species and N nutrition on each trait were determined. The roots of Populus popularis (Pp) were more sensitive to low N, whereas, P. deltoids (Pd) had the highest root biomass irrespective of N levels. The root morphological traits (e.g., total root surface area, total root length, root volume, and fine root surface area) were more affected by the genotype than N levels, and were positively correlated with low N. Conversely, photosynthesis and biomass accumulation in aerial parts were positively correlated with high N and were more affected by soil N availabilities. Considerable morphological variations existed among the analyzed poplar species, and contributed more to the interspecific variations than the physiological traits in these poplar species. The highest NUE was found in Pp under low N, and the lowest one was detected in Pd under high N. In addition, Pearson correlation analysis revealed that most morphological and physiological traits were tightly correlated with NUE among these poplar species in response to changes in N levels. These results indicate that interspecific variations exist within these poplar species, and that NUE is more affected by the N nutrition status than genotype.