Fig. 2From: Morphological, physiological, and transcriptional responses to low nitrogen stress in Populus deltoides Marsh. clones with contrasting nitrogen use efficiencyEffects of low N stress on leaf morphology and chlorophyll content of N-efficient (A-1, A-2, and A-3) and N-inefficient (C-1, C-2, and C-3) genotypes. Different letters above the columns indicate significant differences between the groups (p < 0.05). (A) Chlorophyll (a + b) (Chl); (B) Leaf area (LA)Back to article page