Sulfide effects on Thalassia testudinum carbon balance and adenylate energy charge

Sulfide accumulation in carbonate sediments of tropical seagrass communities may be responsible for widespread die-back of Thalassia testudinum in Florida Bay. Root hydroponic chambers were used to determine the effects of below-ground exposure to 0.0, 2.0, 4.0, 6.0, and 10.0 mM sulfides. T. testudinum ATP, energy charge, photosynthesis and growth responses were determined after 48 h under light saturation. Root ATP, energy charge and adenylate ratios were all significantly reduced (P < 0.05) when exposed to 2.0-10.0 mM sulfides. Leaf elongation rates declined by an average of 43% in the 2.0-6.0 mM treatments and 63% in the 10.0 mM treatment. Although root energy charge, ATP production and leaf elongation rates declined after sulfide exposure, concentrations up to 10.0 mM failed to produce visual signs of sulfide toxicity or mortality. Photosynthesis and leaf EC remained high after sulfide treatments, suggesting a resilience of T. testudinum to short-term sulfide exposure.