Decomposition of macrophytes

Aquatic macrophytes play a crucial role in freshwater carbon (C) cycling by converting inorganic to organic C through photosynthesis. During senescence, macrophyte organic matter accumulates at the sediment surface where it can either be decomposed or buried for longer periods. One of the major factors affecting the decomposition of aquatic macrophytes is its nutritional quality for microbes. This nutritional quality of a specific macrophyte species is dependent on the C:nitrogen (N) and C:phosphorus (P) ratio as well as its content of polyphenols. As polyphenols are C-rich compounds, plant phenolic content can be linked to plant C:nutrient stoichiometry. In general, plants with a high C:nutrient ratio are of low nutritional value for decomposers and thus may have a high potential for long-term burial. However, there is currently no consensus on whether C:nutrient ratio or phenolic content is the most important trait for macrophyte decomposition. Indeed, both these biochemical traits can vary strongly between species, and with environmental gradients. Polyphenols have furthermore antibacterial properties, thereby affecting bacterial biomass and leading to lower bacterial diversity. This can in turn feedback to reduced decomposition rates. Therefore, we aim to unravel how C:nutrient ratios, polyphenol content and bacteria interact on macrophyte decomposition.