Kasper Elgetti Brodersen

Roskilde University

Seagrasses can enhance nutrient mobilization in their rhizosphere via complex interactions with sediment redox conditions and microbial populations. Yet, limited knowledge exists on how seagrass-derived rhizosphere dynamics affect nitrogen cycling. Using optode and gel-sampler-based chemical imaging, we show that radial O 2 loss (ROL) from rhizomes...

Seagrasses provide crucial ecosystem services of relevance for the marine environment. However, anthropogenic activities are causing global seagrass decline. Increasing microplastic (MP) concentrations have been recognized as a novel threat to many marine organisms, but their effects on marine plants remain underexplored. Here, we investigate the e...

In many terrestrial seeds, photosynthetic activity supplies O2 to the developing plant embryo to sustain aerobic metabolism and enhance biosynthetic activity. However, whether seagrass seeds possess similar photosynthetic capacity to alleviate intra‐seed hypoxic stress conditions is unknown. We used a novel combination of microscale variable chloro...

In many terrestrial seeds, photosynthetic activity supplies O 2 to the developing plant embryo to sustain aerobic metabolism and enhance biosynthetic activity. However, whether seagrass seeds possess similar photosynthetic capacity to alleviate intra-seed hypoxic stress conditions is unknown. We used a novel combination of microscale variable chlor...

Epiphytic biofilms on seagrass leaves can lead to extreme microenvironmental conditions for the encapsulated leaf limiting both its photosynthesis and respiration. Yet, little is known about how the biological activity of the biofilm itself changes the seagrass phyllosphere microenvironment and dynamics. We used microsensors to measure O2 concentra...

Ocean warming along with nutrient enrichment are major stressors causing global seagrass decline. While the effects of global warming on metabolic parameters in seagrasses are well described, the effect of increasing temperature on the epiphytic overgrowth of seagrass leaves and the consequences for the seagrass plant are poorly understood. Here, w...

The seagrass phyllosphere consists of a dynamic mosaic of physico-chemical microgradients that modulate light harvesting, gas and nutrient exchange between the photosynthetic leaves and the surrounding water-column. The phyllosphere is thus of vital importance for seagrass growth and fitness. However, unfavorable environmental conditions such as wa...

Freshwater wetlands are natural sinks of carbon; yet, wetland conversion for agricultural uses can shift these carbon sinks into large sources of greenhouse gases. We know that the anthropogenic alteration of wetland hydrology and the broad use of N-fertilizers can modify biogeochemical cycling, however, the extent of their combined effect on green...

Steep geochemical gradients surround roots and rhizomes of seagrass and protect the plants against the harsh conditions in anoxic sediment, while enabling nutrient uptake. Imbalance of these gradients, due to e.g., low plant performance and/or changing sediment biogeochemical conditions, can lead to plant stress and large-scale seagrass meadow die-...

Seagrass ecosystems are globally-significant ‘blue carbon’ sinks; however, there is concern that this capacity will decline if rising ocean temperatures accelerate microbial decomposition. Decomposition of plant litter is a key process in the global carbon cycle—it influences how much carbon is available for sequestration. Therefore, understanding...

Intensified coastal eutrophication can result in an overgrowth of seagrass leaves by epiphytes, which is a major threat to seagrass habitats worldwide, but little is known about how epiphytic biofilms affect the seagrass phyllosphere. The physico-chemical microenvironment of Zostera marina L. leaves with and without epiphytes was mapped with electr...

Eutrophication leads to epiphyte blooms on seagrass leafs, which strongly affect plant health, yet the actual mechanisms of such epiphyte‐induced plant stress remain poorly understood. We used magnetic optical sensor nanoparticles in combination with luminescence lifetime imaging to map the O2 concentration and dynamics in the heterogeneous seagras...

Coastal eutrophication is a growing problem worldwide, leading to increased epiphyte overgrowth of seagrass leaves. Yet, little is known about how epiphytes affect key biogeochemical conditions and processes in the seagrass phyllosphere. We used electrochemical microsensors to measure microgradients of O2, pH, and CO2 at the bare and epiphyte‐cover...

Irradiance and temperature variations during tidal cycles modulate microphytobenthic primary production potentially by changing the radiative energy balance of photosynthetic mats between immersion and emersion and thus sediment daily net metabolism. To test the effect of tidal stages on the radiative energy budget, we used microsensor measurements...

Vegetated coastal habitats (VCHs), such as mangrove forests, salt marshes and seagrass meadows, have the ability to capture and store carbon in the sediment for millennia, and thus have high potential for mitigating global carbon emissions. Carbon sequestration and storage is inherently linked to the geochemical conditions created by a variety of m...

Most aquatic systems rely on a multitude of biogeochemical processes that are coupled with each other in a complex and dynamic manner. To understand such processes, minimally invasive analytical tools are required that allow continuous, real-time measurements of individual reactions in these complex systems. Optical chemical sensors can be used in...

Life in seawater presents several challenges for seagrasses owing to low O2 and CO2 solubility and slow gas diffusion rates. Seagrasses have evolved numerous adaptations to these environmental conditions including porous tissue providing low-resistance internal gas channels (aerenchyma) and carbon concentration mechanisms involving the enzyme carbo...

Seagrasses have a unique leaf morphology where the major site for chloroplasts is in the epidermal cells , stomata are absent and aerenchyma is present inside the epidermis. This means that the major site for photosynthesis is in the epidermis. Furthermore the lack of stomata means that the route for carbon uptake is via inorganic carbon (Ci) uptak...

Seagrasses are a diverse group of angiosperms that evolved to live in shallow coastal waters, an environment regularly subjected to changes in oxygen, carbon dioxide and irradiance. Zostera muelleri is the dominant species in south-eastern Australia, and is critical for healthy coastal ecosystems. Despite its ecological importance, little is known...

The seagrass rhizosphere harbors dynamic microenvironments, where plant‐driven gradients of O2 and dissolved organic carbon form microhabitats that select for distinct microbial communities. To examine how seagrass‐mediated alterations of rhizosphere geochemistry affect microbial communities at the microscale level, we applied 16S rRNA amplicon seq...

Irradiance and temperature changes during tidal cycles affect microphytobenthic primary production potentially changing the radiative energy balance in the photosynthetic biofilm between immersion and emersion. To test this hypothesis, we estimated for the first time the radiative energy budget in a photosynthetic microbial mat during immersion and...

Materials & Methods and Supplementary Data (Figs. S1-10).

Tropical seagrasses are nutrient limited owing to the strong phosphorus fixation capacity of carbonate-rich sediments, yet they form densely-vegetated, multi-species meadows in oligotrophic tropical waters. Using a novel combination of high-resolution, two-dimensional chemical imaging of O2, pH, iron, sulphide, calcium and phosphorus, we found that...

Seagrass species form important marine and estuarine habitats providing valuable ecosystem services and functions. Coastal zones that are increasingly impacted by anthropogenic development have experienced substantial declines in seagrass abundance around the world. Australia, which has some of the world’s largest seagrass meadows and is home to ov...

HIGHLIGHTS: Sedimentation of fine sediment particles onto seagrass leaves severely hampers the plants' performance in both light and darkness, due to inadequate internal plant aeration and intrusion of phytotoxic H2S. Anthropogenic activities leading to sediment re-suspension can have adverse effects on adjacent seagrass meadows, owing to reduced...

We investigated the radiative energy budgets of a heterogeneous photosynthetic coral reef sediment and a compact uniform cyanobacterial biofilm on top of coastal sediment. By combining electrochemical, thermocouple and fiber-optic microsensor measurements of O2, temperature and light, we could calculate the proportion of the absorbed light energy t...

We investigated the radiative energy budgets of a heterogeneous photosynthetic coral reef sediment and a compact uniform cyanobacterial biofilm on top of coastal sediment. By combining electrochemical, thermocouple and fiber-optic microsensor measurements of O 2 , temperature and light, we could calculate the proportion of the absorbed light energy...

A novel dual optode for the simultaneous imaging of pH and O2 was developed to study correlating changes in complex biological systems such as microbial mats and the rhizosphere of seagrasses. The system was tested under lab conditions and optimized to allow monitoring of real life samples by introducing an additional signal enhancing, as well as a...

Nanoparticle based imaging of O2 and pH around the roots of seagrasses

Seagrasses can modulate the geochemical conditions in their immediate rhizosphere through the release of chemical compounds from their below‐ground tissue. This is a vital chemical defence mechanism, whereby the plants detoxify the surrounding sediment. Using novel nanoparticle‐based optical O 2 and pH sensors incorporated in reduced and transparen...

Over the past century, seagrasses have faced an alarming global decline, owing to both direct and indirect human interference [1]. Seagrasses inhabit organic rich, reduced sediments and the exposure of their below-ground biomass to sediment-derived hydrogen sulfide (H2S), has been identified as a key factor in seagrass die-back events [2]. This eff...

The O2 budget of seagrasses is regulated by a complex interaction between several sources and sinks, which is strongly regulated by light availability and mass transfer over the diffusive boundary layer (DBL) surrounding the plant. Epiphyte growth on leaves may thus strongly affect the O2 availability of the seagrass plant and its capability to aer...

Seagrasses provide important eco-engineering services in coastal environments but have over the past century been declining with alarming rates mainly due to anthropogenic activity. Seagrasses are constantly challenged to aerate their belowground tissue and the surrounding sediment to prevent intrusion of reduced, phytotoxic compounds, such as hydr...

Seagrass communities provide important ecosystems services in coastal environments but are threatened by anthropo-genic 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....

Seagrass meadows constitute globally important marine ecosystems; supporting high marine biodiversity and protecting coastal areas from erosion. Over the past century, the worldwide extent of seagrass meadows have declined with an alarming rate, and in order to better manage these vital marine habitats for long-term preservation, new insight into t...

Seagrass is constantly challenged with transporting sufficient O2 from above- to belowground tissue via aerenchyma in order to maintain aerobic metabolism and provide protection against phytotoxins. Electrochemical microsensors were used in combination with a custom-made experimental chamber to analyse the belowground biogeochemical microenvironmen...

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...

The light field on coral reefs varies in intensity and spectral composition, and is the key regulating factor for phototrophic reef organisms, for example scleractinian corals harbouring microalgal symbionts. However, the actual efficiency of light utilization in corals and the mechanisms affecting the radiative energy budget of corals are underexp...