Editorial: Ecophysiology and Biogeochemistry of Marine Plants in the Anthropocene


Editorial Article in Frontiers in Marine Science

“Future climate conditions will arguably have major impacts on the function and fitness of vegetated coastal ecosystems worldwide and thus on their ecological roles. Gaining a better understanding of the environmental regulation of marine plants and their ecophysiology is thus important for the planning of climate adaptation strategies and development of innovative and sustainable protection strategies for marine plants to better protect and secure vital ecosystem services and functions of vegetated coastal ecosystems in the Anthropocene. The Research Topic is a compilation of 14 articles that aim to advance our understanding of how changing environmental conditions in the Anthropocene affects the ecophysiology and biogeochemistry of marine plants. The Research Topic is divided into 3 subtopics: (i) articles that discuss effects on the phyllosphere and rhizosphere conditions, (ii) articles that focus on impacts of ocean warming on marine plants and ecosystems, and (iii) articles that studied effects on seagrass metabolism and biogeochemical cycling.”


Link: https://www.frontiersin.org/articles/10.3389/fmars.2022.1010651/full

Thanks to the Villum Foundation for supporting my research!

Talk at the World Seagrass Conference 2022

14th biennial International World Seagrass Conference and Seagrass Biology Workshop (ISBW14) in Annapolis, Maryland (USA) in 2022.

I will be giving my talk on “Effects of Epiphytes on the Seagrass Phyllosphere” on Tuesday (Aug 9) in the Microbial Ecology session (7B) in the afternoon (between 4-5.30pm).

KEB presentation


Talk entitled:


Kasper Elgetti Brodersen1 and Michael Kühl1

1Marine Biological Section, University of Copenhagen, Copenhagen, Denmark


Eutrophication is a major threat to seagrasses worldwide, as it leads to increased epiphyte overgrowth of leaves. Yet, little is known about how epiphytes affect key biogeochemical processes and chemical conditions in the seagrass phyllosphere. We used microsensors to measure microgradients of O2, temperature, pH, nitric oxide and CO2 at the bare and epiphyte-covered leaf surface of Zostera marina. Epiphytes result in extreme daily fluctuations in pH, O2 and inorganic carbon concentrations at the leaf surface, severely hampering the seagrass’ performance. In light, the presence of epiphytes resulted in strong phyllosphere basification, which reduced the CO2 and HCO3 availability at the leaf surface and reduced photosynthetic efficiency due to carbon limitation and enhanced photorespiration, which increases the risk for plant starvation. With epiphytes, leaf surface pH increased to >10, thereby exceeding final pH levels of ~9.62 and CO2 compensation points for photosynthesis. Epiphytes also impeded heat transfer between the leaf surface and the surrounding water, leading to the establishment of thermal boundary layers (TBLs) and leaf warming. The TBL imposes an insulating barrier impeding heat dissipation from the leaf, potentially aggravating negative responses to elevated temperatures, when seagrasses are living close to their thermal stress threshold. In darkness, epiphytes resulted in increased CO2 and hypoxia at the leaf surface – increasing the risk of plant/tissue asphyxiation. Moreover, anoxic conditions in the leaf epiphytic biofilm at night can also enable anaerobic microbial processes leading to harmful nitric oxide production via denitrification. Epiphytes can thus represent a severe threat to seagrass health.

Effects of epiphytic biofilm activity on the photosynthetic activity, pH and inorganic carbon microenvironment of seagrass leaves (Zostera marina L.)

New paper published in Frontiers in Marine Science

Epiphytic biofilms increase pH and O2 levels in the seagrass leaf microenvironment in the light and strongly reduce the CO2 availability for the underlying seagrass leaf, which leads to reduced leaf photosynthesis and thus seagrass fitness. Here, we aimed at separating the physical and biological contribution of the epiphytic biofilm to the change in phyllosphere conditions and show that the metabolic (biological) activity of epiphytes primarily affected the phyllosphere chemistry in light, leading to hyperoxia and low inorganic carbon conditions, where the epiphytes contributed with the vast majority of the photosynthetic O2 production and thereby to the changes in the seagrass phyllosphere. At night-time, passive diffusion of O2 into the epiphytic biofilm seemed sufficient to meet the epiphytes respiratory needs and therefore had limited effect on the phyllosphere O2 and DIC conditions.

We also aimed at providing first determinations of seagrass leaf DBL acidification via proton pumps, however, such earlier proposed carbon concentration mechanism in seagrass was not supported by our detailed microscale pH measurements.


Thanks to the Villum Foundation for supporting my research!

Link to the paper: https://www.frontiersin.org/articles/10.3389/fmars.2022.835381/full

How to cite: Zhang Q, Kühl M, Brodersen KE (2022). Effects of Epiphytic Biofilm Activity on the Photosynthetic Activity, pH and Inorganic Carbon Microenvironment of Seagrass Leaves (Zostera marina L.). Frontiers in Marine Science.

Temperature effects on leaf and epiphyte photosynthesis, bicarbonate use and diel O2 budgets of the seagrass Zostera marina L.

New paper published in Frontiers in Marine Science

The effect of increasing temperature on the seagrass leaf/epiphyte relationship is poorly understood. Here, we describe temperature effects on leaf and epiphyte photosynthesis, respiration, light requirements, bicarbonate use, and diel O2 balance of the common temperate seagrass species Zostera marina. We show that bare seagrass leaves are less affected by elevated temperatures than leaves with epiphytes and epiphytes removed from Z. marina seagrass leaves, as indicated by a more positive diel O2 balance, higher light use efficiency and lower light requirements. Increased epiphyte growth on seagrass leaves can thus aggravate other effects of climate change and strongly affect plant fitness.

Fig 3 O2 budget v3

Thanks to the Villum Foundation for supporting my research!

Link to the paper: https://www.frontiersin.org/articles/10.3389/fmars.2022.822485/full

How to cite: Hansen AB, Pedersen AS, Kühl M and Brodersen KE (2022) Temperature Effects on Leaf and Epiphyte Photosynthesis, Bicarbonate Use and Diel O2 Budgets of the Seagrass Zostera marina L.. Front. Mar. Sci. 9:822485. 

Effects of Epiphytes on the Seagrass Phyllosphere

New paper published in Frontiers in Marine Science


The seagrass phyllosphere is arguably a key site for gas and nutrient exchange with the surrounding environment. Radiative and mass transfer across the phyllosphere largely determine rates of photosynthesis and respiration in seagrass leaves, affecting seagrass growth and fitness via primary production and internal plant aeration, especially of the below-ground tissue that is anchored in anoxic sediment. Development and application of microanalytical tools has enabled novel insights to the phyllosphere microenvironment. In this mini-review, we summarize current knowledge of the seagrass phyllosphere habitat and how it is affected by eutrophication-driven epiphytic biofilm communities and changing environmental conditions.


Thanks to the Villum Foundation for supporting my research.

Link to the paper: https://www.frontiersin.org/articles/10.3389/fmars.2022.821614/full

How to cite: Brodersen KE and Kühl M (2022) Effects of Epiphytes on the Seagrass Phyllosphere. Front. Mar. Sci. 9:821614. doi: 10.3389/fmars.2022.821614


The combined effect of short-term hydrological and N-fertilization manipulation of wetlands on CO2, CH4, and N2O emissions

New paper accepted for publication in Environmental Pollution


“Our study investigated agricultural use of wetlands and the effects of simulated physico-chemical disturbances and short-term hydrological restoration on wetland CO2, CH4, N2O emissions, as well as, oxygen consumption. We assessed how physical (i.e. drainage) and chemical (i.e. use of N-fertilizers) disturbances influence the production and emission of CO2, CH4 and N2O. Furthermore, we examined the short-term response of wetland hydrological rehabilitation on greenhouse gas (GHG) emissions. We found that soil samples enriched with fertilizer acted as carbon sources, with overall 40% higher CO2 emissions detected under permanently dry conditions, and overall ˃90% higher CH4 and N2O emissions from partially and permanently wet soil samples. Increasing GHG emissions after disturbances can be explained with: (1) predominant oxic conditions after water removal that stimulated microbial degradation rates of organic matter, and (2) high O2 consumption rates (leading to anoxic sediment conditions) and high ammonium availability stimulated microbial respiration that increased nitrifier denitrification activity and the ammonium inhibition of CH4 oxidation. Our results thus suggest that anthropogenic impacts can rapidly alter biogeochemical dynamics in wetlands, leading to increasing global warming potential (up to 7.5-fold), while the combinations of hydrological rehabilitation and high nitrogen loads significantly amplified CH4 and N2O emissions. Therefore, consideration of the timing of both water availability and nitrogen fertilization is needed for agricultural-adjacent wetlands to avoid rapid and extensive release of GHG.”


Thanks to the Blue Carbon Lab [Link] and the Carlsberg Foundation [Link] for collaboration and for supporting my research, respectively.

Link to the paper: https://www.sciencedirect.com/science/article/pii/S0269749121022193

How to cite: Bonetti G, Limpert KE, Brodersen KE, Trevathan-Tackett SM, Carnell PE, Macreadie PI (2021). The combined effect of short-term hydrological and N-fertilization manipulation of wetlands on CO2, CH4, and N2O emissions. Environmental Pollution:118637. doi:https://doi.org/10.1016/j.envpol.2021.118637

Resolving chemical gradients around seagrass roots – a review of available methods

New Paper published in Frontiers in Marine Science


In this mini-review we provide an overview of approaches to investigate the complex, diurnally changing chemical microenvironment around the seagrass roots and rhizome. We discuss each technique (this is, optodes, gels and microsensors) and their associated set-ups while focusing on the practical aspects. By doing so, we identified knowledge gaps and point towards techniques which have not yet been used in seagrass research. Studies of the below-ground biogeochemistry are important to fully understand the response of seagrass to e.g., human impact.

Thanks to Villumfonden for supporting my research!

Link: https://www.frontiersin.org/articles/10.3389/fmars.2021.771382/abstract

Citation: Scholz VV, Brodersen KE, Kühl M and Koren K (2021). Resolving chemical gradients around seagrass roots – a review of available methods. Front. Mar. Sci. 0:1597. doi: 10.3389/fmars.2021.771382

Effects of elevated temperature on microbial breakdown of seagrass leaf and tea litter biomass

New Paper published in Biogeochemistry in collaboration with the Blue Carbon Lab (w/ Stacey TT and Peter Macreadie):

“We used natural seagrass and standardised tea litters of varying chemical recalcitrance, combined with highly-sensitive microsensor technology, to track carbon breakdown. We showed that labile types of litter (e.g. green tea) have a near-immediate Q10 response to elevated temperature, both for the metabolic and decay responses. Warming temperatures had a relatively smaller effect for the more recalcitrant litters (seagrass leaf, rooibos tea), affecting the decomposition process later on in incubation. Our results show that increased temperatures (+5-10°C) have the potential to weaken blue carbon accumulation rates by reducing the quantity of organic carbon coming from fresh litter. These results are timely and novel as they are advancing our mechanistic understanding of how blue carbon sink capacity can be impacted under future climatic conditions.”

Thanks to Carlsbergfondet for supporting my research!

Link: https://link.springer.com/article/10.1007/s10533-020-00715-1

Cite as: Trevathan-Tackett, S.M., Brodersen, K.E. & Macreadie, P.I. Effects of elevated temperature on microbial breakdown of seagrass leaf and tea litter biomass. Biogeochemistry (2020). https://doi.org/10.1007/s10533-020-00715-1

Flow and epiphyte growth effects on the thermal, optical and chemical microenvironment in the leaf phyllosphere of seagrass


New paper in Journal of The Royal Society Interface!!!

Our study investigated how epiphytes affect the seagrass leaf surface microenvironment under different flow and light conditions. We hypothesized that the presence of epiphytes leads to sub-optimal conditions for productivity of Z. marina leaves due to shading in light and local toxic conditions (e.g. anoxia) during darkness.

We used microsensors to measure oxygen, light, and for the first time temperature and nitric oxide microprofiles in the seagrass phyllosphere to characterize how epiphytes modify the physico-chemical microenvironement in the vicinity of seagrass leaves.  We show the first demonstration of temperature boundary layers at the surface of illuminated seagrass leafs. Furthermore, we present the first data on nitric oxide production in epiphytic biofilms during night time anoxic conditions in the phyllosphere, potentially impairing seagrass functioning.

Seagrass meadows are highly important marine ecosystems that provide major ecosystem services in terms of enhancing marine biodiversity, sequestration of carbon and coastal protection. Currently, seagrass meadows are declining with alarming rates worldwide, mainly threatened by deteriorating water quality due to eutrophication and other anthropogenic stressors. Eutrophication promotes epiphyte blooms and increasing overgrowth of seagrass leaves. A better understanding of the detrimental effects of epiphytes on seagrass can help to better predict changes in ecosystem services of seagrass meadows subject to eutrophication.

Thanks to Carlsbergfondet and Villum Fonden for supporting my research! 🙂

Link: https://royalsocietypublishing.org/doi/10.1098/rsif.2020.0485

Cite as: Noisette F, Depetris A, Kühl M, Brodersen KE. (2020). Flow and epiphyte growth effects on the thermal, optical and chemical microenvironment in the leaf phyllosphere of seagrass (Zostera marina). J. R. Soc. Interface 17: 20200485. http://dx.doi.org/10.1098/rsif.2020.0485