Silicon accumulation controls carbon cycle in wetlands through modifying nutrients stoichiometry and lignin synthesis of Phragmites australis

Abstract

Silicon (Si) is one of the most abundant elements in the Earth's crust but its role in governing the biogeochemical cycling of other elements remains poor understood. There is a paucity of information on the role of Si in wetland plants, and how this may alter wetland C production and storage. Therefore, this study investigated Si distribution, nutrient stoichiometry and lignin abundance in Phragmites australis from a wetland system in China to better understand the biogeochemical cycling and C storage. Our data show that Si content (ranging between 0.202% to 6.614%) of Phragmites australis is negatively correlated with C concentration (38.150%–47.220%). Furthermore, Si content was negatively antagonistically related to the concentration of lignin-derived phenols in the stem (66.763–120.670 mg g-1 C) and sheath (65.400–114.118 mg g-1 C), but only a weak relationship was observed in the leaf tissue (36.439–55.905 mg g-1 C), which is relevant to the photosynthesis or stabilization function of the plant tissues. These results support the notion that biogenic Si (BSi) can substitute lignin as a structural component, due to their similar eco-physiological functions, reduces costs associated with lignin biosynthesis. The accumulation of BSi increased total biomass C storage and nutrient accumulation due to greater productivity of Phragmites australis. On the other hand, BSi regulated litter composition and quality (e.g., nutrient stoichiometry and lignin) that provide a possibility for the factors affecting litter decomposition. Thus competing processes (i.e., biomass quantity vs quality) can be influenced by Si cycling in wetlands.