Biology Reference
In-Depth Information
Since nitrogen availability is considered to be a limiting factor in plant
productivity, N fertilization has been used to improve harvest yields and
biomass production. At the same time, human activities are increasing
N levels in the environment, including forest ecosystems (
Tilman et al.,
2001
). N fertilization or luxuriant supply induces dramatic changes in
whole-plant architecture, biomass accumulation and plant metabolism
(
Cooke et al., 2005
). The impact of nitrogen fertilization on lignification
has been documented in forage grasses in relation to their nutritional value
and contrasting responses have been observed. N fertilization had no effect
on the forage lignin content in Trifolium subterraneum and rice (
Nori et al.,
2006; Sanz et al., 2005
) but resulted in increased lignin content in tall fescue
(Festuca arundinacea;
Wolf and von Boberfeld, 2003
). However, the devel-
opmental stage of the plant at the time of N application may also modulate
the response. For instance, late-season N application to tall fescue main-
tained the forage in a physiologically younger stage and led to accumulation
of lower amounts of lignin.
The impact of N supply on lignification has also been studied in woody
species. The effects depend on the species, developmental stage and mode of
N application. N fertilization reduced the lignin content in roots but had no
effect on needles and stems of 1-year-old longleaf pine seedlings (
Entry et al.,
1998
). Wood lignin content was not affected in coppices of P. nigra fertilized
with N (
Luo et al., 2008
) nor in young spruce by a 3-year N fertilization
(
H¨ttenschwiller et al., 1996
) whereas, a long-term nutrient fertilization
(N, P, K, Mg) led to increased lignin content in wood of 41-year-old Norway
spruces (
Kostiainen et al., 2004
). A detailed analysis on poplar grown under
controlled conditions showed that the lignin structure may be altered in the
wood of trees under N fertilization (
Pitre et al., 2007
). Short-term (28-day)
N fertilization induced modifications in wood anatomy, especially thicker cell
walls. Lignin content in the newly formed wood decreased and its structure
was similar to that of tension wood lignin, with a reduced S/G ratio as well as a
reduced frequency of
-O-4 bonds. In a comparison between high-Nwood and
tension wood, transcriptomic analyses suggest that high nitrogen fertilization
and tension wood formation induce largely distinct molecular pathways albeit
with partial overlap (
Pitre et al., 2010
). Consistent with reduced lignification
and S/G ratio, F5H and COMT were downregulated in high N wood and
tension wood compared to low-N normal wood. Interestingly, in a phenotypic
analysis of 396 genotypes from an interspecific pseudo-backcross pedigree of
Populus, N fertilization significantly decreased lignin content in wood together
with S/G ratio (
Novaes et al., 2009
). Quantitative trait loci corresponding to
lignin content and S/G ratio were specific for one of the two nitrogen treatments
demonstrating a significant nitrogen-dependent genetic control.
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