Decomposition and nutrient variations of Suaeda salsa litters under different hydrological connectivities and placement patterns in a typical Chinese estuary

Abstract

A 200-day tethered litter experiment was performed to evaluate the effects of two dimensions of hydrological connectivity (lateral and longitudinal, two perpendicular dimensions) and three placement treatments (surface, semi-buried, and buried) on Suaeda salsa litter decomposition and nutrient release. We used the hydrodynamic condition to represent hydrological connectivity. Mass loss in semi-buried and buried treatments was higher than the surface treatment (p < 0.05), and the former two were basically the same except for the area farthest from the tidal creek. The enhancement of lateral hydrological connectivity significantly accelerated mass loss under the surface and semi-buried treatments (p < 0.05). Sulfur (S) and nitrogen (N) concentrations in the surface treatment were higher than another two treatments in most cases. N concentrations increased with enhancing lateral hydrological connectivity, while potassium (K) concentrations showed a decreasing trend under stronger hydrological connectivity. Phosphorus (P) and S concentrations were not affected by hydrological connectivity. The amount of nutrient release increased with the enhancement of the lateral hydrological connectivity in the surface and semi-buried treatments except for N, and the longitudinal hydrological connectivity only influenced K under the surface treatments. The amount of nutrient release under the surface treatments was lower than another two treatments (p < 0.05). Our findings suggest that the lateral hydrological connectivity has a greater impact on mass loss and nutrient release than the longitudinal hydrological connectivity. If Suaeda. salsa litters are excessively exposed to soil, decomposition processes would increase rapidly and the effects of hydrological connectivity might become minimal.