Black cottonwood (BC, Populus trichocarpa)
and hybrid aspen (HA, P. tremula 9 tremuloides) differ in
their ecology of being adapted to wet and drier conditions
as riparian and early successional forest species, respectively.
We tested the hypothesis that these ecological differences
were reflected in higher nitrogen (N) use
efficiency in HA than in BC and that HA would allocate
more resources belowground than BC in the presence of
high and low N availability. We expected that responses of
wood properties to elevated N would be more pronounced
in the species with higher wood formation in response to N
supply. HA showed higher belowground biomass partitioning
than BC in the presence of low (0.2 mM) and high
(2 mM) N supply, but in contrast to our expectation wholeplant
nitrogen use efficiency and the stem carbon-tonitrogen
balance were lower than in BC. In response to
elevated N, HA exhibited stronger stimulation of biomass
production than BC, especially of the stem, which showed
significant increases in biomass and volume but decreases
in density. Lignification, especially the production of
guaiacyl (G)-compared to syringyl (S)-lignin, was delayed
in HA compared with BC wood. Since G lignin leads to
stronger crosslinking than S lignin, its delayed formation
may have enabled stronger expansion and higher volume
increment of HA than of BC stems. Our results suggest that
BC, a poplar species adapted to fluctuating N supply, is less
responsive to differences in N availability than aspen that
occurs in low N environments.peerReviewe