Our results indicate that the effects of AgNP-exposure on maize
and on the bacterial community in its rhizosphere are negatively
correlated. After 75 days, maize plants showed significantly higher
dry biomass production when they were exposed to AgNP. Additionally,
after both 39 and 75 days, maize total leaf length was
significantly higher under AgNP-exposure. Notably, at those two
harvesting points, the bacterial rhizosphere community exhibited
significant changes under AgNP-exposure. Carbon use diversity
decreased and shifted, and the community structure, as determined
by DNA fingerprinting, changed significantly. These changes
are also apparent from the FDA-assay, showing that the total microbial
activity was significantly lowered by AgNP-exposure only at
these two harvesting points. This decrease in activity indicates that
the changes in the microbial community are caused by the negative
effects of AgNP on bacteria, which in general have a higher activity
level than fungi. The correlation between bacterial community and
plant responses is visible in Fig. 6A, as the AgNP-related shift in
community fingerprint as well as the bacterial metabolic parameters
are negatively correlated with the plant parameters.