Sulfide intrusion in seagrasses assessed by stable sulfur isotopes—a synthesis of current results

Abstract

Sulfide intrusion in seagrasses, as assessed by stable sulfur isotope signals, is widespread in all climate zones, where seagrasses are growing. Seagrasses can incorporate substantial amounts of 34 S-depleted sulfide into their tissues with up to 87% of the total sulfur in leaves derived from sedimentary sulfide. Correlations between 34 δ S in leaves, rhizomes, and roots show that sedimentary sulfide is entering through the roots, either in the form of sulfide or sulfate, and translocated to the rhizomes and the leaves. The total sulfur content of the seagrasses increases as the proportion of sedimentary sulfide in the plant increases, and accumulation of elemental sulfur (S 0 ) inside the plant with 34 δ S values similar to the sedimentary sulfide suggests that S 0 is an important reoxidation product of the sedimentary sulfide. The accumulation of S 0 can, however, not account for the increase in sulfur in the tissue, and other sulfur containing compounds such as thiols, organic sulfur, and sulfate contribute to the accumulated sulfur pool. Experimental studies with seagrasses exposed to environmental and biological stressors show decreasing 34 δ S in the tissues along with reduction in growth parameters, suggesting that sulfide intrusion can affect seagrass performance.

Light indirectly mediates bivalve habitat modification and impacts on seagrass

“…5A). Both indicators of sulfide intrusion that were measured in this mesocosm study (F sulfide and root S 0 ) are similar to values observed in situ for Zostera marina Borum et al, 2013;Holmer and Hasler-Sheetal, 2014), suggesting that similar sulfur dynamics may occur in coastal regions of the North and Baltic Seas.…”

Climate Change Impacts on Seagrass Meadows and Macroalgal Forests: An Integrative Perspective on Acclimation and Adaptation Potential

“…Although this metabolic shift allows the system to recycle organic carbon, it comes at a high cost by generating high amounts of sulfide that is toxic for seagrasses (Koch and Erskine, 2001). Seagrasses are able to tolerate sulfide intrusion by: (i) reoxidized sulfide by oxygen present in the aerenchyma (Pedersen et al, 2004) or in the rhizosphere (van der Heide et al, 2012) or (ii) organic sulfur conversion into thiols (Holmer and Hasler-Sheetal, 2014). If both mechanisms fail and sulfide intrudes into active tissues such as leaves and meristems, seagrasses suffer in performance (Garcias-Bonet et al, 2008;Pulido and Borum, 2010).…”

“…If the plant cannot translocate sucrose efficiently to feed the underground organs, it will consume the storage sugars (underground starch) to maintain root growth and nutrient acquisition metabolisms. This re-mobilization of underground starch shifts the plant metabolism from an energy producer to an active consumer and, thus, impairs growth and primary productivity (Holmer and Bondgaard, 2001;Koch and Erskine, 2001;Holmer and Hasler-Sheetal, 2014).…”

Epiphyte-cover on seagrass (Zostera marina L.) leaves impedes plant performance and radial O2 loss from the below-ground tissue

“…Bacterially-mediated H 2 S oxidation is about 10.000-100.000 times faster than the chemical reaction alone (Jørgensen and Postgate, 1982) and therefore has potential to be of high value for the plants. It has been suggested that H 2 S oxidation also takes place inside the plant (Holmer et al, 2005;Holmer and Hasler-Sheetal, 2014), as seagrass exposed to high sediment H 2 S levels showed internal accumulation of elemental sulfur that is an intermediate in the sulfide oxidation. This process is, however, driven by simple chemical reactions between H 2 S and O 2 and is not mediated by intra-plant enzymes or bacteria (Pedersen et al, 2004) as seen in some marine invertebrates (Grieshaber and Völkel, 1998).…”