Impacts on Nematode Pests - Climate Resilient Agriculture for Ensuring Food Security - page 179

from dauer stage or diapause, etc. Elevated CO 2
levels may also infl uence these nematodes
indirectly by altering host physiology (defense
mechanisms such as production of secondary
metabolites and nutrient status such as C:N ratio).
It may also infl uence microbial feeding nema-
todes due to changes in quality and availability of
food under enriched CO 2 conditions in soil.
The impacts of climate change can be positive,
negative, or neutral, since these changes can
decrease, increase, or have no impact on nema-
tode abundance, depending on each region or
period.
Available information on effect of global
warming on soil nematodes though limited indi-
cates that abundance of soil nematodes in general
is either increased or unaffected by elevated CO 2
levels, while individual species and trophic
groups differ considerably in their response to
climate change. Herbivorous nematodes showed
neutral or positive response to CO 2 enrichment
effects with some species showing the potential
to build up rapidly and interfere with plant's
response to global warming.
Similar to other organisms which feed on
plants, increased CO 2 levels are believed to have
an impact on herbivorous nematodes (Ayres et al.
2008 ), and several studies have been conducted,
where the aboveground plant community was
exposed to elevated CO 2 . Almost all of these
studies were done in different grasslands and for-
ests, and thus results have been variable and con-
tradictory. Research results regarding nematodes,
from experiments conducted on agricultural
crops in arable soils, are very limited. Basically,
all kinds of results were determined: increase,
decrease, and no change of nematode populations
(Sticht et al. 2009 ). A recent publication presents
results of a long-term agricultural experiment
conducted in winter wheat and sugar beets in
Germany. Winter wheat and sugar beet were
grown in rotation under 550 ppm atmospheric
CO 2 compared to ambient (380 ppm) atmospheric
CO 2 . The number of herbivore, bacterivore, and
fungivore nematodes was signifi cantly higher
under wheat and sugar beets grown under ele-
vated CO 2 , while the number of carnivore was
not changed. The total numbers of herbivore,

bacterivore, and fungivore nematodes were
higher under elevated CO 2 wheat than under ele-
vated CO 2 sugar beet, most likely due to the very
different root system of both plant species (Sticht
et al. 2009 ). However, impacts on yield were not
determined.
The observations that elevated CO 2 levels
often induce increased root production. It can be
presumed that herbivorous nematode communi-
ties will be relatively more affected by increases
in atmospheric CO 2 concentration. Positive
effects of CO 2 enrichment on the abundance of
herbivorous nematodes have been reported in
some studies (Yeates et al. 2003 ). The abundance
of Tylenchus and Longidorus increased after
5 years of CO 2 enrichment, but there was no
effect on the abundance of Paratylenchus ,
Trichodorus , and members of Hoplolaimidae in
pasture plots (Yeates et al. 2003 ). Yeates et al.
( 1997 ) reported increase in abundance of
Meloidogyne in response to CO 2 enrichment in
grassland turfs while 7 other herbivorous nema-
tode taxa were not affected. The abundance of
Pratylenchus was positively associated with CO 2
concentration in gley, but not in organic soil
around a natural CO 2 vent in New Zealand
(Yeates et al. 1999 ).
Although root biomass increased under ele-
vated CO 2 , the damage due to root-feeding
nematodes was more under elevated CO 2 com-
pared to the ambient levels in a grass species
(Wilsey 2001 ). Similarly, neutral responses of
herbivorous nematodes to CO 2 enrichment were
observed despite increase in root production by
3-32 % in different locations (Ayres et al.
2008 ). This may be due to decrease in root
quality (low nitrogen content) or increase in
nematode antagonists.
The interaction of elevated CO 2 with nitro-
gen fertilization or residue addition signifi -
cantly affected the soil nematode community
indices. The residue addition stimulated struc-
ture index and inhibited plant-parasite response
to the elevated CO 2 in a wheat fi eld (Li et al.
2009 ).
Experiments with rice have showed no adverse
effects of elevated CO 2 levels up to 700 ppm on
the abundance of soil nematodes and penetration