Biology Reference
In-Depth Information
The lignin modifications induced by CAD or COMT downregulation in
transgenic poplars (P. tremula
P. alba) had no unexpected biological or
ecological impacts. Interactions with leaf-feeding insects, microbial pathogens
and soil organisms were unaltered (
Halpin et al., 2007
). Likewise, no difference
in the diversity of the soil bacterial community could be found (
Halpin et al.,
2007; Pilate et al., 2002
). While a preliminary study has shown that lignin
modifications resulted in higher rates of root decomposition than in the wild
type (
Pilate et al., 2002
), it was later demonstrated that only in the short-term,
decomposition rate of roots in the soil was slightly increased for the most
affected trees, suggesting that the lignin modification led to a decreased ability
of modified lignins to protect polysaccharides from microbial attack: this
actually occurs during the first step of decomposition, whereas in the long-
term, such differences were no longer apparent (
Hopkins et al., 2007
). In
addition, the decomposition in soils of sections of trunks from similar trans-
genic trees did not reveal any significant differences in total CO
2
production or
in total mass loss from the trunk material (
Tilston et al., 2004
). Otherwise, the
evaluation of the same transgenic lines revealed that effects of the different
genetic modifications on leaf litter quality, its decomposition rate, and coloni-
zation by aquatic insects in three natural Scandinavian streams, were shown to
be small compared to variations due to environmental conditions (
Axelsson
et al., 2010
).
Finally, the diversity of fungal communities associated with poplar roots
from field-grown transgenic poplar lines with suppressed expression of CAD,
COMT (
Pilate et al., 2002
)orCCR (
Lepl´ et al., 2007
) was evaluated by a
metagenomic approach using 454-pyrosequencing. It appeared that none of
the genetic modifications had any impact on the diversity of ectomycorrhizal
fungi. The only significantly lower diversity indices measured for one trans-
genic line was most likely related to its altered biomass production suggesting a
link between plant productivity and fungal diversity (
Danielsen et al., 2011
).
Feeding preferences and growth performances of common boreal insect
herbivores (Lepidoptera and Coleoptera) were evaluated on the leaves of
transgenic COMT-downregulated silver birch (Betula pendula Roth) with
lower S/G ratio in their lignins. On average, but not significantly, lowest
growth rates for two species were measured when larvae was fed on leaves
with G-rich lignins, suggesting a negative effect of the lignin modification on
leaf digestibility (
Tiimonen et al., 2005
). Overall, this study led the authors to
conclude that, despite variations of feeding preferences of insect herbivores
among the different birch lines, feeding preferences were not directly asso-
ciated with lignin modification. Although scarce, all these preliminary studies
led to the conclusion that lignin-modified trees have little or no effect on these
trophic interactions.
