Wetland plant species tissue chemistry associated with pore water sulfur in contrasting hydrogeologic settings

Background/Question/Methods Sulfur is an essential plant nutrient, but it can also be a plant toxin or mediate the availability of other elements to plants. The predominant role of sulfur is highly dependent on the magnitude of sulfur supply and the form of sulfur, both of which show tremendous variability within freshwater wetlands. Interacting effects of sulfur on plants can be both direct (e.g., sulfide or sulfate as a toxin or nutrient) and indirect (e.g., iron-mediated effects of sulfur on phosphorus availability or heavy metal availability). We hypothesized that direct plant accumulation of sulfur and indirect plant accumulation of phosphorus would show species-specific patterns associated with variations in porewater sulfur chemistry. We measured porewater sulfate and sulfide chemistry in calcareous rich fens with contrasting hydrogeologic settings (sulfur-rich gypsic geology vs. sulfur-poor calcitic geology) and correlated this porewater chemistry with plant tissue sulfur and phosphorus in both the roots and shoots of the following three species: Eupatorium maculatum, Solidago patula, and Typha latifolia.

Results/Conclusions Wetland plant tissue sulfur correlations with porewater sulfate and sulfide were highly dependent on species identity, while wetland plant tissue phosphorus correlations with porewater sulfate and sulfide were more uniform across species. More specifically, tissue sulfur in E. maculatum shoots was highly positively correlated with porewater sulfate (R²=0.86), while tissue sulfur in S. patula and T. latifolia was not significantly related to porewater sulfate, suggesting that E. maculatum has limited capacity to regulate sulfur uptake. Porewater sulfide was significantly positively correlated with plant root phosphorus (R²=0.38), but contrary to expectations porewater sulfide was not significantly correlated with plant shoot phosphorus. The increase in root tissue phosphorus for all three species with increasing porewater sulfide is consistent with the expectation that these species would be phosphorus limited and that they would respond to the indirect mobilization of iron-bound phosphorus by sulfide. More work is needed to determine the relative importance of porewater sulfate and sulfide in shaping the spatial distribution of plant species in calcareous rich fens.