Effects of coastal embankments on seasonal variations in nitrogen storage in the plant-soil systems of Suaeda salsa salt marshes in Eastern China

The impacts of coastal embankments on nitrogen (N) dynamics are of great importance in salt marshes. However, effects of embankments on seasonal N dynamics in the plant-soil systems of Suaeda salsa salt marshes are still not well understood. Therefore, the edaphic moisture and salinity, biomass, N concentrations and storage in different plant tissues; the extent of organic and inorganic N subpools in soil subsystems; as well as N immobilization and mineralization by microorganisms in embanked and neighboring natural S. salsa salt marshes through all four seasons were investigated in Yancheng, Eastern China. Our results revealed that embankments increased the biomass and N storage of dead tissues (e.g., litter), while they decreased the biomass and N storage of live tissues (e.g., living aboveground tissues and roots) of S. salsa through decreased edaphic moisture and salinity. Furthermore, under the influence of embankments edaphic water-dissolvable N, e.g.,edaphic dissolved organic N (EDON) and nitrate and nitrite N (TNN), significantly increased with higher N inputs from S. salsa litter. This water-dissolvable N was an important source of N for plants, which translated to higher N concentrations in live plant tissues. However, this excess absorbed N appeared not to facilitate the growth of plants, which would ultimately return to the soil from plant residues. Our results suggested that the decreased edaphic soil moisture and salinity due to embankments had negative impacts on the biomass and N storage of S. salsa plant tissues, which were likely due to shifts in the edaphic osmotic potential. Subsequently, a cascading butterfly effect may be initiated due to the impaired growth of S. salsa, to which more attention should be paid. This study represents a step forward by providing valuable insights and an improved elucidation of the seasonal plant-soil N dynamics of S. salsa salt marshes.