Effects of nitrogen enrichment on variations of sulfur in plant-soil system of Suaeda salsa in coastal marsh of the Yellow River estuary, China

Abstract

Abstract To assess the impacts of nitrogen (N) enrichment on sulfur (S) allocations and turnovers in Suaeda salsa marsh in high tidal flat of the northern Yellow River estuary, the variations of S in plant-soil system were investigated by conducting in situ experiment of N enrichment which included four treatments (N0, no N import treatment, 0 g N·m−2·yr−1; N1, low N import treatment, 3.0 g N·m−2·yr−1; N2, middle N import treatment, 6.0 g N·m−2·yr−1; and N3, high N import treatment, 12.0 g N·m−2·yr−1). Results showed that although N enrichment did not alter the temporal variations of TS contents in soils greatly, higher values were generally observed in N2 and N3 treatments. Increased N loading promoted the mineralization of S in marsh soils, but, as soils were flooded, the potentially mineralizable S in soils declined significantly and the decreasing amplitude was particularly evident in N2 treatment. With increasing N enrichment, the biomasses of different organs during the growing season generally showed an increasing tendency, but the contents of TS in organs showed dissimilar variations. Except for N1 treatment, stocks of S in plant-soil systems showed an increasing tendency with increasing N loading. Compared with N0 treatment, stocks of S in plant subsystem increased by 18.03%, 20.81% and 59.18% at N1, N2 and N3 treatments, respectively, while those in soils at N2 and N3 treatments increased by 0.61% and 2.68%, respectively. Both S absorption coefficients (SAC) and utilization coefficients (SUC) of plants generally showed increasing tendency with increasing N enrichment, and, compared to N0 treatment, the SAC at N1, N2 and N3 treatments increased by 61.83%, 94.83% and 86.85%, respectively, whereas the SUC at the three treatments increased by 4.07%, 25.42% and 14.28%, respectively. This paper found that, with increasing N enrichment, the S. salsa might adjust its growth traits and S allocations to adapt different N import conditions and the adaptation strategy was particularly evident in plants at N2 treatment. In future, as N loading reached N2 level, the S supply relationships between aboveground and belowground tissues of S. salsa and the patterns of S allocations in its plant-soil system would be altered greatly, which might directly influence the stability and health of S. salsa marsh ecosystem.