Nitrogen metabolism and antioxidant system responses of Suaeda salsa to nitrogen addition

There are serious problems with degradation of Suaeda salsa (S. salsa) in Liaohe estuary wetland, Liaodong Bay, Northeast China, which may be mainly caused by the high nitrogen runoff of the upstream ecosystem. This study investigated the effect of nitrogen addition on the nitrogen transformation of S. salsa and soil by 15N labeling technology and the oxidative stress to S. salsa, thereby exploring the cause of the degradation. The dry weight (by 45.2%–67.3%) of S. salsa and the abundance of ammonium monooxygenase (amoB) (by 62%–75%) gene in soil decreased under high concentration of nitrogen conditions. The dissolved organic nitrogen (DON) (by 3%–14.2%) and total nitrogen (TN) (by 75%–89.7%) content in soil increased with increasing nitrogen addition. The hydrogen peroxide (by 5.9%–14.6%) and malondialdehyde (MDA) (by 9.6%–14.7%) content of S. salsa increased with increasing nitrogen addition. Therefore, high concentration of nitrogen not only decreased the biomass of S. salsa but also caused the waste of nitrogen source. High concentration of nitrogen weakened the nitrification of soil microorganisms and caused oxidative stress to S. salsa. The addition of high concentration of nitrogen was evidenced to be one of the main reasons for the degradation of S. salsa in the present study.