Does Nutrient Availability Regulate Seagrass Response to Elevated CO2?
Future increases in oceanic carbon dioxide concentrations (CO2(aq)) may provide a benefit to submerged plants by alleviating photosynthetic carbon limitation. However, other environmental factors (for example, nutrient availability) may alter how seagrasses respond to CO2(aq) by regulating the supply of additional resources required to support growth. Thus, questions remain in regard to how other factors influence CO2(aq) effects on submerged vegetation. This study factorially manipulated CO2(aq) and nutrient availability, in situ, within a subtropical seagrass bed for 350 days, and examined treatment effects on leaf productivity, shoot density, above- and belowground biomass, nutrient content, carbohydrate storage, and sediment organic carbon (Corg). Clear, open-top chambers were used to replicate CO2(aq) forecasts for the year 2100, whereas nutrient availability was manipulated via sediment amendments of nitrogen (N) and phosphorus (P) fertilizer. We provide modest evidence of a CO2 effect, which increased seagrass aboveground biomass. CO2(aq) enrichment had no effect on nutrient content, carbohydrate storage, or sediment Corg content. Nutrient addition increased leaf productivity and leaf N content, however did not alter above- or belowground biomass, shoot density, carbohydrate storage, or Corg content. Treatment interactions were not significant, and thus NP availability did not influence seagrass responses to elevated CO2(aq). This study demonstrates that long-term carbon enrichment may alter the structure of shallow seagrass meadows, even in relatively nutrient-poor, oligotrophic systems.
Keywordsocean acidification reduced pH carbon dioxide climate change carbon storage Thalassia testudinum
We thank Dr. Patrick Rice and the Florida Keys Community College for logistical support. Jennifer Sweatman, Bryan Dewsbury, Nathan Lemoine and Thomas Frankovich provided assistance in the field. This work was conducted in the Florida Keys National Marine Sanctuary under permits FKNMS-2010-015 and FKNMS-2010-015A and was supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research Program under Grant No. DBI-0620409, and a Graduate School Doctoral Evidence Acquisition Fellowship awarded to J.E.C by Florida International University. This is contribution #74 from the Marine Education and Research Center in the Institute for Water and Environment at Florida International University.
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