Planar Optode Research Articles

Oxygen imaging at the sediment‐water interface using lifetime‐based laser induced fluorescence (τLIF) of nano‐sized particles

AbstractMost applications of laser induced fluorescence (LIF) for dissolved oxygen (DO) imaging in flowing water are based on luminescence intensity measurements of a dissolved indicator. A major limitation for applying the technique in the bottom boundary layer (BBL) is the sorption of the luminescent dye to organic surfaces at the sediment. Many sediment and soil studies have used planar optodes on transparent foils as an imaging technique for observing concentration distributions across the sediment‐water interface. The presence of the foil, however, is restricting the free flow and therewith the DO concentration above the sediment surface. In this study, we applied the phosphorescence lifetime LIF (τLIF) technique in combination with nanoparticles coated with platinum complexes as DO indicators. By using a planar laser light sheet for fluorescence excitation, the three‐dimensional flow field around the sampling area is not restricted. In contrast to the intensity‐based LIF technique, this method extracts the lifetime of the luminescence by evaluating the exponential decrease of the phosphorescence intensity after a short excitation light pulse. The method is therefore independent of dye concentration and is not affected by spatial inhomogeneities of the excitation light intensity. We applied the technique to visualize the burrow‐ventilation activity of the tube‐dwelling Chironomus plumosus larvae. Sequences of the two‐dimensional DO concentration distributions showed the intermittent outburst of highly‐depleted plumes from the outlet of the burrows, which mixed rapidly with the ambient oxygen‐rich water.

Spatiotemporal dynamics of phosphorus release, oxygen consumption and greenhouse gas emissions after localised soil amendment with organic fertilisers

Organic fertilisation inevitably leads to heterogeneous distribution of organic matter and nutrients in soil, i.e. due to uneven surface spreading or inhomogeneous incorporation. The resulting localised hotspots of nutrient application will induce various biotic and abiotic nutrient turnover processes and fixation in the residuesphere, giving rise to distinct differences in nutrient availability, soil oxygen content and greenhouse gas (GHG) production. In this study we investigated the spatiotemporal dynamics of the reaction of manure solids and manure solids char with soil, focusing on their phosphorus (P) availability, as current emphasis on improving societal P efficiency through recycling waste or bio-based fertilisers necessitates a sound understanding of their behaviour. Soil layers amended at a constant P application rate with either pig manure solids or char made from pig manure solids were incubated for three weeks between layers of non-amended, P-depleted soil. Spatial and temporal changes in and around the amendment layers were simultaneously investigated in this study using a sandwich sensor consisting of a planar oxygen optode and multi-element diffusive gradients in thin films (DGT) gels, combined with GHG emission measurements. After three weeks of incubation, the soil containing a layer amended with manure solids had a lower overall O2 content and had emitted significantly more CO2 than the non-amended control or the char-amended soil. The P availability from manure solids was initially higher than that from the char, but decreased over time, whereas from the char-amended layer P availability increased in the same period. In both treatments, increases in P availability were confined to the amended soil layer and did not greatly affect P availability in the directly adjacent soil layers during the three-week incubation. These results highlight the importance of placing organic P fertilisers close to where the plant roots will grow in order to facilitate optimal fertiliser use efficiency.

A nitrate sensitive planar optode; performance and interferences

We present a newly developed nitrate sensitive planar optode. It exhibits a linear response to nitrate from 1 to 50mM at pH 8.0, a fast response time below 10s and a good lifetime, allowing for fast two dimensional nitrate measurements over long periods of time. Interference from nitrite, chloride and thiocyanate, however, limits the optode’s application in environments where these are encountered, notably seawater with its high chloride content.

(Keynote) Oxygen Sensing Microfluidic Structures for Biomedical and Environmental Science Research

Planar optode films consisting of a fluorescent dye in a polymer film can be incorporated into microfluidic structures to map out oxygen concentrations while microfluidic devices set up gradients and environmental conditions that are relevant to biomedical or natural biogeochemical systems. Gradients of molecular oxygen are of particular interest due to the fact that many important biological processes either occur at interfaces or are regulated by the flux of oxygen and other resources. Hence, oxygen sensing microfluidic devices can be used to investigate microbial behavior related to carbon cycling, or microbial communities in the gut where the interface with the host tissue is microoxic. In addition, oxygen sensing microfluidic devices may be useful in mammalian cell or tissue culture where favorable conditions must be maintained. Practical issues in developing and fabricating microfluidic structures with inherent oxygen sensing capability include multiple parameters, including incorporation of sensing elements in microfluidics, imaging oxygen concentrations by fluorescence, and relating oxygen imaging data to spatial structure of the microfluidic channels, all in useful structures that create biologically relevant microenvironments. We will describe multiple approaches to meeting these challenges, including gas impermeable silicon-on-glass structures where the fluorescent signals are only observed where microfluidic channels occur, and solvent imprinting lithography where sensing dyes can be incorporated in thermoplastics in a single process that enables sensor dye impregnation, channel imprinting, and cover plate bonding. These methods are discussed with regard to structures including pore network and gradient generation microfluidic structures.

Heterogeneity of O2 dynamics in soil amended with animal manure and implications for greenhouse gas emissions

Soil oxygen (O2) availability influences nitrification and denitrification, the major biological processes responsible for nitrous oxide (N2O) production and emissions from soil. In this study O2-specific planar optodes were used to visualise O2 distribution with high spatial and temporal resolution in soils in which the same amount of solid fraction of pig manure had been distributed in three different ways (mixed, layered, single patch) and which were maintained at a water potential of −5 kPa (corresponding to 91% of water-filled pore space). In parallel, the greenhouse gas emissions (N2O, CO2 and CH4) from soil at high temporal resolution were monitored. At the end of the incubations, vertical profiles of mineral nitrogen (ammonium and nitrate) in the soil matrix were quantified. The optode results revealed that anoxia rapidly developed in zones with manure addition and gradually expanded to the entire soil during the 66-h experimental period. The anoxia in the soil developed more quickly as the heterogeneity of manure distribution decreased (from single patch to layered to mixed). The single patch distribution of manure solids delayed peak emission rates of both N2O and CO2, but stimulated the cumulative N2O emissions and reduced the cumulative CO2 fluxes. The faster the anoxia developed, the less the nitrification process appeared to contribute to N2O emissions. No treatment effects on CH4 emissions were observed. Combined high resolution imaging of O2 dynamics and measurements of N2O emission rates are essential to get a detailed understanding of how O2 availability regulates the distribution and coupling of denitrification and nitrification activity in soil. Such unique information on soil O2 dynamics could be used for further modelling and quantification of processes producing greenhouse gases from soil ecosystems.

O2 dynamics in the rhizosphere of young rice plants (Oryza sativa L.) as studied by planar optodes.

Background and aimsRadial O2 loss (ROL) strongly affect the O2 availability in the rhizosphere of rice. The ROL create an oxic zone around the roots, protecting the plant from toxic reduced chemical species and regulates the redox chemistry in the soil. This study investigates the spatio-temporal variability in O2 dynamics in the rice rhizosphere.MethodApplying high-resolution planar optode imaging, we investigated the O2 dynamics of plants grown in water saturated soil, as a function of ambient O2 level, irradiance and plant development, for submerged and emerged plants.ResultsO2 leakage was heterogeneously distributed with zones of intense leakage around roots tips and young developing roots. While the majority of roots exhibited high ROL others remained surrounded by anoxic soil. ROL was affected by ambient O2 levels around the plant, as well as irradiance, indicating a direct influence of photosynthetic activity on ROL. At onset of darkness, oxia in the rhizosphere was drastically reduced, but subsequently oxia gradually increased, presumably as root and/or soil respiration declined.ConclusionThe study demonstrates a high spatio-temporal heterogeneity in rhizosphere O2 dynamics and difference in ROL between different parts of the rhizosphere. The work documents that spatio-temporal measurements are important to fully understand and account for the highly variable O2 dynamics and associated biogeochemical processes and pathways in the rice rhizosphere.

Rhizosphere O2 dynamics in young Zostera marina and Ruppia maritima

Zostera marina and Ruppia maritima often share the same habitat, but R. maritima appears more resistant to environmental stress. We investigated the impact of light intensity and water column O2 concentrations on radial oxygen loss (ROL), in young specimens of Z. marina and R. maritima. Planar optode imaging revealed that ROL of Z. marina was localized to the root tip, while R. maritima showed ROL along extensive root sections. The total root biomass of the 2 spe- cies was similar, but, while R. maritima had only 1 root, of which 33% of its length showed ROL, Z. marina had 2 to 5 individual roots, where only 2 to 3 exhibited O2 leakage, but then only at root tips. ROL resulted in an oxic volume of 4.26 ± 0.51 mm 3 plant �1 for Z. marina and 5.39 ± 0.47 mm 3 plant �1 for R. maritima (n = 3). ROL per plant at light saturation was 2.32 ± 0.30 and 2.89 ± 0.38 nmol h �1 for Z. marina and R. maritima, respectively. These values declined by 71 and 60% in darkness. However, both species were able to maintain ROL as long as ambient O2 levels remained >50% air saturation. The calculated ROL integrated over a 24 h cycle was 48.8 ± 10.6 nmol O2 plant �1 d �1 (n = 3) for R. maritima and 30% less for Z. marina. The ability of R. mar- itima to maintain higher ROL than Z. marina could be an important feature defining its potential for colonizing and maintaining growth in eutrophic sediments.

Imaging of oxygen transmission in the oak wood of wine barrels using optical sensors and a colour camera

Background and Aims Wine ageing in oak barrels is characterised by a series of physical and chemical processes, in many of which oxygen plays an important role. Therefore, to control better this phase of winemaking, it is not enough to know that oxygen penetrates into the barrel through the oak wood; it is also important to know how oxygen moves through the wood into the barrel, in what quantity and which factors are involved. Methods and Results We attempted to answer these questions with a high-resolution colour camera, ratiometric calibration and a planar optode with which the two-dimensional distribution and dynamics of oxygen within an oak barrel stave were studied. It was possible to make two-dimensional measurements when combined with microscopic optics and an appropriate camera, which permitted the measure of the transmission of oxygen into the barrel through the oak stave and the study of the mechanism of transmission. The trial was applied to both dry and wet oak wood, which revealed how the moisture content of the wood influenced oxygen transmission. The measurements were made in an airtight chamber under controlled temperature and pressure, which accurately reproduced the conditions of a stave in an oak wood barrel filled with liquid. Conclusion We were able to visualise the diffusion of oxygen in both dry and in wet French oak wood under conditions similar to those operating in a barrel. The moisture content of the wood influenced the oxygen transmission rate (OTR) through the wood. Significance of the Study For the first time, the dissolved oxygen dynamics and two-dimensional distribution of oxygen within the thickness of a barrel stave have been demonstrated. Wood water saturation is a key factor in the diffusion of oxygen through wood with barrel OTR decreasing during the ageing period.

A split flow chamber with artificial sediment to examine the below-ground microenvironment of aquatic macrophytes

We present a new experimental set-up enabling fine-scale examination of how changing environmental conditions affect the below-ground biogeochemical microenvironment of aquatic macrophytes. By means of microsensor and planar optode technology, the influence of plant-mediated radial O2 release on the below-ground chemical microenvironment of Zostera muelleri and Halophila ovalis was determined in high spatio-temporal resolution. The seagrass specimens were cultured in a new split flow chamber with artificial sediment made of a deoxygenated seawater–agar solution with added sulphide. Microelectrode measurements revealed radial O2 release from the root–shoot junction of both Z. muelleri and H. ovalis during both light stimulation and darkness, resulting in a rapid decrease in H2S concentration, and a significant drop in pH was observed within the plant-derived oxic microzone of Z. muelleri. No radial O2 release was detectable from the below-ground tissue of Z. muelleri during conditions of combined water-column hypoxia and darkness, leaving the plants more susceptible to sulphide invasion. The spatial O2 heterogeneity within the immediate rhizosphere of Z. muelleri was furthermore determined in two dimensions by means of planar optodes. O2 images revealed a decrease in the spatial extent of the plant-derived oxic microzone surrounding the below-ground tissue during darkness, supporting the microelectrode measurements. This new experimental approach can be applied to all rooted aquatic plants, as it allows for direct visual assessment of the below-ground tissue surface during microprofiling, while enabling modification of the above-ground environmental conditions.

Spatial oxygen distribution and nitrous oxide emissions from soil after manure application: a novel approach using planar optodes.

The availability and spatial distribution of oxygen (O) in agricultural soil are controlling factors in the production and emission of nitrous oxide (NO) to the atmosphere, but most experiments investigating the effects of various factors on NO emissions in soil have been conducted without determining the content and distribution of O. This complicates data interpretation and leads to speculative conclusions about which nitrogen transformation processes are responsible for NO production. Using an O-specific planar optode, this paper shows how spatiotemporal O dynamics can be used to interpret data on NO emissions following a uniform or layered amendment of manure to agricultural soil. The spatial distribution of O and gas emission rates were monitored for 12 h. An anoxic layer formed rapidly around the layered manure, whereas the uniformly distributed manure led to a more widespread anoxia. Nitrous oxide emissions increased immediately after depletion of O in the manure-amended treatments. Greater understanding and improved knowledge of the spatial distribution of O is clearly beneficial and can be used to devise improved application strategies for mitigating NO emissions from manure and other fertilizers.

The Dynamics of Plant-Mediated Sediment Oxygenation in Spartina anglica Rhizospheres—a Planar Optode Study

Belowground sediment oxygenation in rhizospheres of wetland plants promotes nutrient uptake, serve as protection against toxic reduced compounds and play an important role in wetland nutrient cycling. The presence of ~1.5-mm-wide oxic zones around roots of the intertidal marsh grass Spartina anglica was demonstrated below the sediment surface using planar optode technology recording 2D images of the sediment oxygen distribution. Oxic root zones were restricted to the root tips stretching up to 16 mm along the roots with an oxygen concentration up to 85 μmol L−1 detected at the root surface. Radial oxygen loss across the root surface ranged from 250 to 300 nmol m−2 s−1, which is comparable to other wetland plants. During air exposure of the aboveground biomass, atmospheric oxygen was the primary source for belowground oxygen transport, and light availability only had a minor effect on the belowground sediment oxygenation. During inundations completely submerging the aboveground biomass cutting off access to atmospheric oxygen, oxic root zones diminished significantly in the light and were completely eliminated in darkness. Within the time frame of a normal tidal inundation (~1.5 h), photosynthetic oxygen production maintained the presence of oxic root zones in light, whereas oxic root zones were eliminated within 1 h in darkness. The results show that the sediment oxygenation in Spartina anglica rhizospheres is temporally dynamic as well as spatially variable along the roots.

Localized flux maxima of arsenic, lead, and iron around root apices in flooded lowland rice.

In wetland-adapted plants, such as rice, it is typically root apexes, sites of rapid entry for water/nutrients, where radial oxygen losses (ROLs) are highest. Nutrient/toxic metal uptake therefore largely occurs through oxidized zones and pH microgradients. However, the processes controlling the acquisition of trace elements in rice have been difficult to explore experimentally because of a lack of techniques for simultaneously measuring labile trace elements and O2/pH. Here, we use new diffusive gradients in thin films (DGT)/planar optode sandwich sensors deployed in situ on rice roots to demonstrate a new geochemical niche of greatly enhanced As, Pb, and Fe(II) mobilization into solution immediately adjacent to the root tips characterized by O2 enrichment and low pH. Fe(II) mobilization was congruent to that of the peripheral edge of the aerobic root zone, demonstrating that the Fe(II) mobilization maximum only developed in a narrow O2 range as the oxidation front penetrates the reducing soil. The Fe flux to the DGT resin at the root apexes was 3-fold higher than the anaerobic bulk soil and 27 times greater than the aerobic rooting zone. These results provide new evidence for the importance of coupled diffusion and oxidation of Fe in modulating trace metal solubilization, dispersion, and plant uptake.

Root and rhizosphere processes-high time to dig deeper.

Root and rhizosphere processes-high time to dig deeper.

Oxygen dynamics and porewater transport in sediments inhabited by the invasive polychaete Marenzelleria viridis

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 504:181-192 (2014) - DOI: https://doi.org/10.3354/meps10737 Oxygen dynamics and porewater transport in sediments inhabited by the invasive polychaete Marenzelleria viridis Zeljko Jovanovic1, Morten Larsen1,2,3, Cintia Organo Quintana1, Erik Kristensen1, Ronnie N. Glud1,2,3,4,* 1Institute of Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark 2Scottish Association for Marine Science, Dunstaffnage Marine Laboratory, Oban PA37 1QA, UK 3Greenland Climate Research Center (CO Greenland Institute of National Resources), Kivioq 2, Box 570, 3900 Nuuk, Greenland 4Artic Research Center, C. F. Møllers Allè 8, 8000 Aarhus University C, Denmark *Corresponding author: rnglud@biology.sdu.dk ABSTRACT: The polychaete Marenzelleria viridis is an invasive species and often replaces the native Nereis diversicolor. This shift leads to more reduced conditions and changes in the biogeochemical function of the sediments. By combining imaging techniques for O2 (planar optodes) and irrigation patterns (rhodamine WT and brilliant blue), we investigated the relationship between irrigation and O2 dynamics in burrows of M. viridis. The investigated animals shifted between 2 modes of ventilation: ciliary pumping for 77% of the time and muscular pumping for 23% of the time. On average, muscular pumping was induced every 0.4 h. During ciliary pumping, oxic water was pumped into blind-ended burrows and into the surrounding sediment, inducing an upward porewater transport of O2-depleted water. This pattern was reversed during muscular pumping. The 2 pumping modes induced oscillating O2 penetration along the burrow wall and along the primary sediment-water interface. The average net downward irrigation rate, including both pumping modes, amounted to 11.1 × 10-3 ± 2.4 × 10-3 ml min-1. The estimated average oxic sediment volume was 2.1 ± 0.5 cm3 per burrow, and the burrow-specific O2 consumption was 45.6 ± 18.1 nmol min-1. M. viridis burrows and the ambient sediment are relatively O2 depleted, with intensified rates of O2 consumption, compared to similar-sized native N. diversicolor. The complex O2 dynamics induced a unique microenvironment that must favor meiofauna and microbial communities that are tolerant to oxic-anoxic oscillations or that have the ability to migrate along with the pulsing oxic-anoxic interface. KEY WORDS: Bioirrigation · Oxygen dynamics · Marenzelleria viridis · Planar optode · Rhodamine Full text in pdf format PreviousNextCite this article as: Jovanovic Z, Larsen M, Organo Quintana C, Kristensen E, Glud RN (2014) Oxygen dynamics and porewater transport in sediments inhabited by the invasive polychaete Marenzelleria viridis. Mar Ecol Prog Ser 504:181-192. https://doi.org/10.3354/meps10737 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 504. Online publication date: May 14, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Oxygen budgets in subtidal arctic (Kongsfjorden, Svalbard) and temperate (Helgoland, North Sea) microphytobenthic communities

We compared primary production and respiration of temperate (Helgoland, North Sea) and subtidal Arctic (Kongsfjorden, Svalbard) microphytobenthic communities during sum- mer. The diatom communities were generally characterized as cosmopolitan, displayed no site specificity, and had similar chl a and fucoxanthin concentrations. Their net and gross photosynthe- sis rates and light adaptation intensities, derived from laboratory microsensor measurements, were also similar, despite differences in water temperature. Daily oxygen fluxes across the sedi- mentwater interface were estimated by combining laboratory microprofile and planar optode measurements with in situ data on oxygen penetration and light dynamics. During the study period, the Svalbard sediments were on average net heterotrophic, while the Helgoland sediments were net autotrophic (�22.4 vs. 9.2 mmol O2 m �2 d �1 ). This was due to high infaunal abundance in the Svalbard sediments that caused high oxygen uptake rates in the sediments and consumption below the sediment euphotic zone. Additionally, bioirrigation of the sediment due to infaunal burrow ventilation was reduced by light; thus, the sedimentary oxygen inventory was reduced with increasing light. Conversely, light-enhanced the oxygen inventory in the Helgoland sedi- ments. Oxygen dynamics in the Svalbard sediments were therefore dominated by bioirrigation, whereas in the Helgoland sediments they were dominated by photosynthetic oxygen production.

Disentangling who is who during rhizosphere acidification in root interactions: combining fluorescence with optode techniques.

Plant–soil interactions can strongly influence root growth in plants. There is now increasing evidence that root–root interactions can also influence root growth, affecting architecture and root traits such as lateral root formation. Both when species grow alone or in interaction with others, root systems are in turn affected by as well as affect rhizosphere pH. Changes in soil pH have knock-on effects on nutrient availability. A limitation until recently has been the inability to assign species identity to different roots in soil. Combining the planar optode technique with fluorescent plants enables us to distinguish between plant species grown in natural soil and in parallel study pH dynamics in a non-invasive way at the same region of interest (ROI). We measured pH in the rhizosphere of maize and bean in rhizotrons in a climate chamber, with ROIs on roots in proximity to the roots of the other species as well as not-close to the other species. We found clear dynamic changes of pH over time and differences between the two species in rhizosphere acidification. Interestingly, when roots of the two species were interacting, the degree of acidification or alkalization compared to bulk soil was less strong then when roots were not growing in the vicinity of the other species. This cutting-edge approach can help provide a better understanding of plant–plant and plant–soil interactions.

RGB color ratiomatric planar optode로 측정한 표층 퇴적물의 2차원 산소 분포

We measured two-dimensional (2-D) oxygen distribution in the surface sediment layer of intertidal sediment using a simple and inexpensive planar oxygen optode, which is based on a color ratiometric image approach. The recorded emission intensity of red color luminophore light significantly changed with oxygen concentration by O₂ quenching of platinum(II)octaethylporphyrin (PtOEP). The ratios between the intensity of red and green emissions with oxygen concentration variation demonstrated the Stern-Volmer relationship. The 2-D oxygen distribution image showed microtopographic structure, diffusivity boundary layer and burrow in surface sediment layer. The oxygen penetration depth (OPD) was about 2 mm and the one-dimensional vertical diffusive oxygen uptake (DOU) was 12.6 mmol m -2 d -1 in the undisturbed surface sediment layer. However, those were enhanced near burrow by benthic fauna, and the OPD was two times deeper and DOU was increased by 34%. The simple and inexpensive oxygen planar optode has great application potential in the study of oxygen dynamics with high spatiotemporal resolution, in benthic boundary layers.

Root effects on the spatial and temporal dynamics of oxygen in sand-based laboratory-scale constructed biofilters

It is now well known that roots introduce oxygen into the soil environment through radial oxygen loss. The oxygen dynamics surrounding roots in periodically flushed environments, however, remains unstudied. We investigated the impact of roots of the macrophyte Carex appressa (Cyperaceae), on the small (rhizosphere) scale spatiotemporal dynamics of sediment oxygen consumption in a periodically flushed soil mimicking natural percolation events. Oxygen dynamics around the roots of C. appressa were studied using a planar optode installed in a rhizobox containing sand. A sand-based culture medium was used to simulate conditions in constructed biofiltration wetlands. The use of planar optodes allowed the generation of two dimensional images of sediment oxygen dynamics, that were used to quantify the patterns and kinetics of oxygen consumption. In addition to greatly increasing the spatial heterogeneity of oxygen in the substrate, the area immediately surrounding the roots became sites of both enhanced oxygen consumption, likely due to increased microbial activity associated with the input of carbon-rich rhizodeposits, and radial oxygen loss. This study highlights the profound impact of roots upon sub-surface oxygen dynamics in the rhizosphere.

Visualization of oxygen distribution patterns caused by coral and algae

Planar optodes were used to visualize oxygen distribution patterns associated with a coral reef associated green algae (Chaetomorpha sp.) and a hermatypic coral (Favia sp.) separately, as standalone organisms, and placed in close proximity mimicking coral-algal interactions. Oxygen patterns were assessed in light and dark conditions and under varying flow regimes. The images show discrete high oxygen concentration regions above the organisms during lighted periods and low oxygen in the dark. Size and orientation of these areas were dependent on flow regime. For corals and algae in close proximity the 2D optodes show areas of extremely low oxygen concentration at the interaction interfaces under both dark (18.4 ± 7.7 µmol O2 L- 1) and daylight (97.9 ± 27.5 µmol O2 L- 1) conditions. These images present the first two-dimensional visualization of oxygen gradients generated by benthic reef algae and corals under varying flow conditions and provide a 2D depiction of previously observed hypoxic zones at coral algae interfaces. This approach allows for visualization of locally confined, distinctive alterations of oxygen concentrations facilitated by benthic organisms and provides compelling evidence for hypoxic conditions at coral-algae interaction zones.

Light for the dark side of plant life: —Planar optodes visualizing rhizosphere processes

Background The simple term “rhizosphere” is well defined and has inspired numerous studies from a broad field of science since the beginning of the 20th century. However, we still know very little about the spatial and temporal heterogeneity of rhizosphere processes. This is mostly because assessing rhizosphere heterogeneity is not a trivial task. One technology for high-resolution and quantitative imaging of rhizosphere processes is called planar optode technology. This technology can create quantitative maps of key rhizosphere parameters non-invasively and has great potential to reveal new insights into this biogeochemical hotspot.