Sulfur biological cycle of the different Suaeda salsa marshes in the intertidal zone of the Yellow River estuary, China

To evaluate the sulfur (S) biological cycle status in the marshes of the intertidal zone, this study explored the S biogeochemical processes in the two Suaeda salsa marshes [middle S. salsa marsh (MSM) and low S. salsa marsh (LSM)] of the Yellow River estuary during April 2008 to November 2009. Results showed that soil S fluctuated seasonally and varied with depth in both MSM and LSM. The variations in S content in different parts of plant were significantly influenced by water and salinity. The S. salsa litter in MSM and LSM released S to the decomposition environment throughout the year. The S absorption coefficients of S. salsa in MSM and LSM were very low (0.0031 and 0.0004, respectively), while the S biological cycle coefficients were high (0.9014 and 0.8625, respectively). The S turnovers among compartments of MSM and LSM indicated that the uptake amounts of roots were 1.237 and 0.160 g m−2 yr−1 and the values of aboveground parts were 3.885 and 1.276 g m−2 yr−1, the re-translocation quantities from aboveground parts to roots were 2.770 and 1.138 g m−2 yr−1, the translocation amounts from roots to soil were 0.154 and 0.018 g m−2 yr−1, the translocation quantities from aboveground living bodies to litter were 1.115 and 0.138 g m−2 yr−1, and the annual return quantities from litter to soil were less than 1.096 and 0.188 g m−2 yr−1, respectively. Although S was not a limiting nutrient in S. salsa marshes, its high biological cycle rate might significantly inhibit the production and emission of methane (CH4), which had important significances to reduce CH4 emission from the Yellow River estuary. The S quantitative relationships determined in the compartment model might provide some scientific basis for us to reveal the special inhibition mechanism in future studies.