Thesis
Degradation and remineralisation of detritus from macroalga (Ecklonia radiata) and the potential role of fungi
Southern Cross University
Doctor of Philosophy (PhD), Southern Cross University
2022
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Abstract
Coastal regions are dynamic sites of biogeochemical cycling that influence the climate through organic matter (OM) degradation, which affects coastal carbon storage (blue carbon). Although seagrasses and mangroves are recognised contributors to blue carbon, macroalgae have been largely overlooked, mainly because macroalgae grow on rocky substrate that limits detritus burial, and macroalgal detritus is rapidly degraded. However, macroalgae are highly productive and macroalgal detritus (wrack) is frequently deposited on beaches, where its degradation could impact coastal carbon cycles and blue carbon. Pathways for wrack degradation are poorly understood. Fungal pathways may be important for wrack degradation, but are little studied in coastal and marine environments.
Here, macroalgal degradation (Ecklonia radiata) on a beach was simulated using flow-through mesocosms to investigate and quantify biogeochemical pathways. Mesocosms were then run with and without the addition of fungicide to investigate the role of fungi in kelp wrack degradation, and endophytic fungi from E. radiata were screened for their degradation potential (ability to degrade organic polymers) under oxic and anoxic conditions.
Mesocosm studies suggested that macroalgal leachate on a beach would first enter porewater as dissolved organic carbon (DOC) (~60% per mass) which would be partly remineralised into dissolved inorganic carbon (~16%) at 100 cm sediment depth while emitting only a small amount of CO2 and CH4 (<2%). A significant pathway for macroalgal carbon was its conversion to carbonate alkalinity (23% by day 45 and 27% by day 60 per mass). Together, the alkalinity, DOC and DIC produced during macroalgal decomposition may represent a significant blue carbon source. The produced alkalinity would increase the buffering capacity of the coastal ocean by absorbing atmospheric CO2. The produced DOC could have a long residence time (up to 4,000 to 6000 years), while the released DIC can be converted into bicarbonate with a potential oceanic residence time of ca. 100,000 years. However, the contribution of alkalinity, DOC, and DIC to blue carbon would depend on environmental and chemical factors.
When fungi were inhibited, significantly less macroalgae was decomposed, and less DIC and carbonate alkalinity was produced. Fungal remineralisation produced substantially higher dimethyl sulfide, and methanethiol, and increased dimethyl sulfoniopropionate 1000x. Based on organic polymer degradation, endophytic fungi from E. radiata potentially decompose macroalgae under oxic and anoxic conditions. Overall, this thesis demonstrates the potential for fungi to contribute to macroalgal decomposition and, in turn, the potential for macroalgae to contribute to coastal carbon offsets (blue carbon).
Details
- Title
- Degradation and remineralisation of detritus from macroalga (Ecklonia radiata) and the potential role of fungi
- Creators
- Anita K. Perkins
- Contributors
- Joanne Oakes (Supervisor) - Southern Cross UniversityRose L. Andrew (Supervisor) - Southern Cross UniversityHans-Peter Grossart (Supervisor) - University of PotsdamBradley D Eyre (Supervisor) - Southern Cross University
- Awarding Institution
- Southern Cross University; Doctor of Philosophy (PhD)
- Theses
- Doctor of Philosophy (PhD), Southern Cross University
- Publisher
- Southern Cross University
- Number of pages
- xxxiv, 232
- Identifiers
- 991013179513202368
- Copyright
- © K A Perkins 2022
- Academic Unit
- Faculty of Science and Engineering
- Resource Type
- Thesis