Effects of Exogenous Nitrogen Enrichment on Distributions of Total Phosphorus in Plant-Soil System of Suaeda salsa Marsh in the Yellow River Estuary during the Growing Season
Nitrogen (N) and phosphorus (P) are two essential nutrients affecting the ecological processes and the stabilization of marsh ecosystems.Compared to N,P plays important roles in many special biogeochemical processes such as synthesizing P-containing compounds (e.g.nucleic acids,phospholipids and ribonucleotide),controlling the metabolism of carbohydrates in photosynthesis process and enhancing the resistance and adaptation to environmental stress.Estuarine marshes are crucial ecosystems in which the material-energy exchanges between continental river water and marine salt water occur and the effects of global climate change and human activities aggravate.Particularly,with the rapid industrialization and economic development in coastal zone,large quantities of pollutants containing N and P are imported into estuary,resulting in great effects on the habitation of flora and fauna in estuarine marsh.The Suaeda salsa marsh in high tidal flat of the northern Yellow River Estuary were selected as study object,and the total phosphorus (TP) in plant-soil system of S.salsa marsh in the Yellow River Estuary as affected by different N input treatments (N0,no N input treatment;N1,low N input treatment;N_2,middle N input treatment;and N3,high N input treatment) was studied by in situ experiment of N input.The results showed that the influence of exogenous N input on the change of TP content in surface soil of the S.salsa marsh was obvious.The TP content in surface soil (0-10 cm) under N2 and N3 treatments was higher than that of N0 and N1 treatments.The TP contents in different organs of S.salsa under different N input treatments generally followed a leaf >root>stem pattern,indicating that leaves were the key tissues of phosphorus (P) accumulation.Exogenous nitrogen input changed the nutrient restriction status in the S.salsa marsh.With the increase in nitrogen input,although the limitation of P nutrient was intensified,the plant might achieve the best distribution of the obtained P nutrients by adjusting its own ecological characteristics.The increment of soil P stock and plant-soil system P stock were much lower than that of plant sub-system P stock and N supply,indicating that the nutrient supply between N and P was inconsistent.This study found that the increasingly severe P nutrient limitation might be alleviated by accelerating the P biological cycling rate of plant-soil system of S.salsa marsh and this,in turn,might form a positive feedback between N and P,which would favor the maintenance of stabilization and health of the marsh ecosystem.