Sulfur isotopic composition (δ³⁴S, mean ± SEM) in per mille [‰] of bulk sulfur, insoluble sulfur compounds (S⁰), organic sulfur, and sulfate in different <i>Zostera marina</i> tissues cultivated under high sediment sulfide concentrations (HS) and control conditions (C); n = 6.

<p>Note that S⁰ was assessed from insoluble sulfur compounds. Asterisks indicate significant differences between HS and C. Capital letters indicate significant differences between compounds within a tissue; lower case letters indicate significant differences between the tissue types in a specific compound. ANOVA and post hoc Tukey’s test; p < 0.05.</p><p>Sulfur isotopic composition (δ³⁴S, mean ± SEM) in per mille [‰] of bulk sulfur, insoluble sulfur compounds (S⁰), organic sulfur, and sulfate in different <i>Zostera marina</i> tissues cultivated under high sediment sulfide concentrations (HS) and control conditions (C); n = 6.</p

Conceptual model of sediment-sulfide intrusion, sulfate uptake, and possible sulfide accumulation/detoxification patterns in <i>Zostera marina</i>.

<p>Dash-dotted lines = gas diffusion; dashed lines = liquid diffusion; circles = inorganic sulfur; rectangles = organic sulfur; diamonds = gaseous compounds; pentagons = detoxified and permanently stored sulfur; ox = oxidation; ez = enzymatic pathway. Symbols marked with a question mark indicate an unknown reaction. Symbols shaded in grey indicate sulfur pools enriched in ³⁴S. White symbols indicate depleted ³⁴S sulfur pools and symbols with a grey/white gradient indicate mixed δ³⁴S pools.</p

Sulfur budget of different fractions of <i>Zostera marina in situ</i> (A) stacked values of all fractions, (B) total sulfur, (C) sulfate, (D) organic sulfur, (E) thiols, (F) S⁰.

<p>Values represent mean ± SEM. Lower case letters indicate differences between tissues (ANOVA and Tukey’s test, p < 0.05); n = 12.</p

Sulfur content in atomic-percent [at%] by SEM-EDX in <i>Zostera marina</i> roots exposed to sulfide intrusion.

<p>Letters indicate significant differences (Dunn's test p < 0.05); n = 48. HS = high sulfide; C = control.</p

Linear regressions of pore water sulfide and <i>Zostera marina</i> tissue sulfate (A, C) and thiol concentration (B, D) from plants exposed to high pore water sulfide concentrations in experimental conditions (A, B) and from field plants (C, D); n = 12 for A, B and 9 for C, D.

<p>DW, dry weight.</p

Relative net accumulation of total sulfur in <i>Zostera marina</i> (HS minus C) including the assemblage total sulfur composition of sulfur compounds in the different tissues (n = 6).

<p>Relative net accumulation of total sulfur in <i>Zostera marina</i> (HS minus C) including the assemblage total sulfur composition of sulfur compounds in the different tissues (n = 6).</p

Sulfur budget of different fractions of <i>Zostera marina in vitro</i> (A) stacked values of all fractions, (B) total sulfur, (C) sulfate, (D) organic sulfur, (E) thiols, (F) S⁰.

<p>Values represent mean ± SEM; n = 6. C, control; DW, dry weight; HS, high sulfide. Columns connected by the asterisk indicate significant intra-tissue differences (ANOVA and Tukey’s test, p < 0.05).</p

Sulfur isotopic response in sulfur compounds in <i>Zostera marina</i> upon sulfide intrusion.

<p>Shift of average δ³⁴S values (± SEM) in per mille [‰] of bulk sulfur and different sulfur compounds from <i>Zostera marina</i> between high sulfide concentrations (HS) and control conditions (C); n = 6. Capital letters indicate significant differences between compounds in a tissue and lower case letters indicate differences between tissues for a specific compound (ANOVA and Tukey’s test, p < 0.05).</p

Conceptual model of sulfide detoxification capacities of <i>Zostera marina</i> exposed to sulfide intrusion based on stable isotope tracing and mass balance modeling.

<p>The numbers (percentage) next to the arrows indicate the contribution of a sulfur compound to the detoxification process. The numbers (percentage) under ‘rel’ indicate the relative distribution of a sulfur compound between the tissues; the numbers under ‘abs’ indicate the share of the net total sulfur accumulation upon sulfide intrusion of the compounds in a tissue. The total sulfur table indicates the share of the different tissues in detoxification of sulfide. Avoidance is indicated by preventing sulfide intrusion by precipitation of sulfide to S⁰ and tolerance by standing sulfide intrusion by incorporating sulfide into thiols, organic sulfur, and sulfate.</p

Appendix A. A figure showing sediment cores with –OM and +OM treatments at the end of the experiment (day 25).

A figure showing sediment cores with –OM and +OM treatments at the end of the experiment (day 25)