Ecophysiology and Biogeochemistry of Marine Plants in the Anthropocene

With ongoing climate change in the Anthropocene, extreme environmental impacts such as ocean deoxygenation, heatwaves, heavy rain and storm events are expected to increase in frequency and severity, leading to detrimental effects on the livelihood of marine plants and their coastal habitats. Hypoxic conditions in the water column, induced by eutrophication or the shoaling of deoxygenated water, markedly affect the intra-plant O2 budget of marine plants, increasing their susceptibility to intrusion of reduced toxic compounds. Coastal eutrophication often results in epiphyte-blooms on seagrass and other marine plant leaves, shading the leaves for light and limiting essential gas and nutrient exchange with the water column. Elevated temperature can weaken the blue carbon sink capacity of vegetated coastal ecosystems and can lead to oxygen deficiency in plants living close to their thermal stress threshold. Increased temperature can also lead to elevated microbial activity producing sulphides increasing the sulphide pressure on the plants and elevated emissions of methane from seagrass sediments, further weakening their climate mitigation capacities. Finally, drops in salinity and high ammonium availability have been shown to synergistically interact to negatively affect marine plant fitness.

Hence, future climate conditions will arguably have major impacts on the health and functioning of vegetated coastal ecosystems worldwide and thus on their ecosystem functions and services. This Research Topic invites studies focusing on effects of climate change and other anthropogenic stressors on the ecophysiology and biogeochemistry of marine plants. This includes original studies, perspectives and mini-reviews of how ocean deoxygenation, increased temperature and eutrophication act alone or in synergy in affecting the fitness of seagrasses and macroalgae in terms of: (i) the plant/epiphyte relationship and performance, (ii) the plant’s photosynthetic efficiency, O2 balance and carbon fixation capacity, (iii) interactions in the plant rhizosphere with sediment biogeochemical processes and chemical conditions, and (iv) the blue carbon sequestration capacity and greenhouse gas emission potential of marine plants. We also encourage papers assessing possible adaptations/acclimations of marine plants to future climate conditions, including molecular studies focusing e.g. on up- and downregulation of enzymes involved in CO2 concentration mechanisms or deoxygenation stress responses in marine plants. Gaining a better understanding of the (micro)environmental ecology of marine plants in the age of changing oceans is important for the planning of climate adaptation strategies and for the development of innovative and sustainable protection strategies for marine plants. This is especially relevant for those growing in coastal waters exposed to anthropogenic disturbances/stress, as it will enable us to better protect and secure vital ecosystem services and functions of vegetated coastal ecosystems in the Anthropocene.

This Research Topic focuses on (but is not limited to) the following aspects:
• Studies addressing extreme environmental events as a stressor for marine plants and vegetated sediments, as well as, on whole ecosystem level.
• Studies of light intensity and quality effects on photosynthetic activity and efficiency.
• Studies of how the relationship between the plants and their epiphytic biofilm community will react and potentially shift as a response to increased nutrient availability and coastal water deoxygenation.
• Studies of how nutrient and temperature increases affects carbon sequestration, decomposition processes and decay rates within the sediment and greenhouse gas emissions from vegetated coastal ecosystems.
• Identification of key molecular responses of marine plants to environmental stress.
• Studies addressing plant-sediment interactions and how these are affected by climate related stressors or anthropogenic disturbances (e.g., dam on a river, harbour development, dredging events, bottom trawling, etc.).
• Studies on plant-to-plant interactions with seagrass meadows, and how these will react and potentially shift as a response to climate change related stressors.
• Studies focusing on interactions of marine plants with biogeochemical element cycling in sediments and how such interactions are affected by climate change and other anthropogenic stressors.