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Download fileOptical Sensor Nanoparticles in Artificial Sediments–A New Tool To Visualize O2 Dynamics around the Rhizome and Roots of Seagrasses
journal contribution
posted on 2015-02-17, 00:00 authored by Klaus Koren, Kasper E. Brodersen, Sofie
L. Jakobsen, Michael KühlSeagrass
communities provide important ecosystems services in coastal
environments but are threatened by anthropogenic impacts. Especially
the ability of seagrasses to aerate their below-ground tissue and
immediate rhizosphere to prevent sulfide intrusion from the surrounding
sediment is critical for their resilience to environmental disturbance.
There is a need for chemical techniques that can map the O2 distribution and dynamics in the seagrass rhizosphere upon environmental
changes and thereby identify critical stress thresholds of e.g. water
flow, turbidity, and O2 conditions in the water phase.
In a novel experimental approach, we incorporated optical O2 sensor nanoparticles into a transparent artificial sediment matrix
consisting of pH-buffered deoxygenated sulfidic agar. Seagrass growth
and photosynthesis was not inhibited in the experimental setup when
the below-ground biomass was immobilized in the artificial sulfidic
sediment with nanoparticles and showed root growth rates (∼5
mm day–1) and photosynthetic quantum yields (∼0.7)
comparable to healthy seagrasses in their natural habitat. We mapped
the real-time below ground O2 distribution and dynamics
in the whole seagrass rhizosphere during experimental manipulation
of light exposure and O2 content in the overlaying water.
Those manipulations showed that oxygen release from the belowground
tissue is much higher in light as compared to darkness and that water
column hypoxia leads to diminished oxygen levels around the rhizome/roots.
Oxygen release was visualized and analyzed on a whole rhizosphere
level, which is a substantial improvement to existing methods relying
on point measurements with O2 microsensors or partial mapping
of the rhizosphere in close contact with a planar O2 optode.
The combined use of optical nanoparticle-based sensors with artificial
sediments enables imaging of chemical microenvironments in the rhizosphere
of aquatic plants at high spatiotemporal resolution with a relatively
simple experimental setup and thus represents a significant methodological
advancement for studies of environmental impacts on aquatic plant
ecophysiology.