Sulfide intrusion and detoxification in seagrasses ecosystems: How to avoid rotting feet

Sulfide intrusion in seagrasses represents a global threat to seagrasses and thereby an important parameter in resilience of seagrass ecosystems. In contrast seegrasses colonize and grow in hostile sediments, where they are constantly exposed to invasion of toxic gaseous sulfide. Remarkably little is known about the strategies of seagrasses to survive sulfide intrusion, their potential detoxification mechanisms and sulfur nutrition in general.
By a global review of sulfide intrusion, coupled with a series of field studies and in situ experiments we elucidate sulfide intrusion and different strategies of seagrasses to sustain sulfide intrusion. Using stable isotope tracing, scanning electron microscopy with x-ray analysis, tracing sulfur compounds combined with ecosystem parameters we found different spatial, intraspecific and interspecific strategies to cope with sulfidic sediments. 1) Tolerance, by elimination (eg. Zostera marina); where we found precipitation of sulfide as non-toxic elemental sulfur on the inner wall of the root lacunae. 2) Utilization (eg. Z. marina), where seagrasses detoxify and incorporate sulfides by active uptake and metabolize to sulfate, representing a non-toxic storage compound. 3) Avoidance, by barriers in tissue (eg. suberin layers in Posidonia) and/or radial root oxygen loss to reoxidize sulfide. Foliar sulfate and metabolic uptake of gaseous sulfide via roots as main sulfur source represents an evolutionary adaption of submerged plants, to our knowledge not present in terrestrial plants at that level. Sulfide is not necessarily toxic but used as sulfur nutrition, presupposing healthy seagrass ecosystems that can support detoxification mechanisms. Presence or absence of those mechanisms determines susceptibility of seagrass ecosystems to sediment sulfide and thereby their resilience, which is important knowledge for management of seagrasses under global pressure.