The extensive interaction platform between microbes and
plants that exists in the rhizosphere, is already known to have farreaching
implications for both partners. Our results show a maize
biomass increase in case of AgNP-exposure, but only when also the
bacterial community in its rhizosphere undergoes significant alterations
and the fungal community remains largely unchanged.
The rhizosphere microbial community apparently is altered in
a way that benefits maize growth. This can originate from a
diverse array of either increased plant-beneficial characteristics or
decreased plant-disadvantageous properties in the rhizosphere
microbial community, mainly mediated by shifts in the bacterial
community. There has been significant focus on AgNP in phytopathogens
management research (Servin et al., 2015), and phytopathogen
suppression is also a possible explanation for the AgNPinduced
increase in plant growth. However, other microorganismmediated
processes such as fungal proliferation, suggested above,
and increased mycorrhization are equally likely to explain the
observed effects. Additional research is needed to unambiguously
state the mechanism behind the AgNP-induced plant growth increase.
Our results highlight the importance of rhizosphere interactions
and additionally pose that these interactions have
important consequences for the impact of foreign substances such
as AgNP on multiple members of the system. Several kinds of NPs
have already been shown to directly affect plant growth and productivity
in artificial systems, but the effects of NPs on rootassociated
microbes are very likely to play an important role in
actual terrestrial systems. Clearly, additional investigations
addressing the impacts of widely used materials such as AgNP
should occur under soil-based conditions and the impact of
exposure on plant-associated microbial communities should be
included in fate and effects assessment.