Agriculture Reference
In-Depth Information
The germination and root elongation of several of the species were enhanced at
lower concentrations but were significantly inhibited (20-30 %) at 2,000 and
4,000 mg/L. However, the shoot elongation was enhanced in nearly all cases.
Birbaum et al. (
2010
) showed that exposure of CeO
2
NPs to corn grown in soil
(50 mL of 10
g/mL CeO
2
NPs per day through irrigation) for 14 days resulted in no
observable toxicity. The authors also included an aerial exposure on leaves, and
similarly corn growth was not affected. Wang et al. (
2012
) grew tomato in the
presence of CeO
2
NP-amended (0.1-10 mg/L) irrigation water throughout the
lifetime of this plant and reported either no impact or slight enhancements in
plant growth and yield. A recent study demonstrated that CeO
2
NPs had a modest
impact on soybean growth in soil but showed a detrimental impact on the nitrogen
fixation bacterial community on soybean roots (Priester et al.
2012
).
Taken together, the impact of ENMs on agricultural crops is highly diverse and
is strongly dependent upon the composition and properties of ENMs, the applied
concentrations of ENMs, the plant species, as well as the growing conditions. One
important observation of the checked literature studies is that most of the toxicity
studies were performed with very high concentrations highly unexpected in the real
environmental conditions in the foreseeable future and in a very short term (from
days to a few weeks). A most likely scenario we will face is that crops will grow in
an environment with low levels of ENMs for many generations; however, the long-
term impact of ENMs on plant growth at environmentally relevant concentrations is
still elusive. Our lab has germinated tomato seeds collected from the mother plants
grown in the presence or absence of 10 mg/L of CeO
2
NPs throughout their life
cycle and then grew the seedlings again hydroponically in the presence and absence
of 10 mg/L of CeO
2
NPs to obtain some insights on the impact of CeO
2
NPs on the
second-generation seedlings. Our study showed that while CeO
2
NPs stimulated the
growth of tomato seedlings developed from unexposed seeds, seedlings developed
from seeds collected from CeO
2
NPs-treated mother plants had smaller biomass,
lower water transpiration, and much higher hydrogen peroxide in their roots (Wang
et al.
2013a
,
b
). Interestingly, the second-generation seedlings grown from treated
mother plant seeds developed significantly more root hair, irrespective of their
exposure to CeO
2
NPs or not in the second generation. We also grew the second-
generation seedlings in suspensions containing different types of ENMs and
observed the root elongation and biomass collection. Our results indicated that
except for seedlings exposed to raw MWCNTs, all second-generation seedlings
developed with seeds from CeO
2
NPs-treated mother plants displayed slower root
elongation (Fig.
14.2
). Plant biomass development demonstrated similar trend as
root elongation (Fig.
14.3
). The only exception is that treated second-generation
tomato seedlings had slightly higher biomass than untreated seedlings 10 days after
their growth in suspensions containing 10 mg/L of C
60
fullerene. These results
clearly showed that the long-term impact of ENMs on plant development varied
with their short-term impact and the long- term, multigenerational impact of ENMs
on plant development should be further investigated.
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