MEPS 387:61-70 (2009)  -  DOI: https://doi.org/10.3354/meps08101

ABSTRACT: Mathematical models were used to quantify annual production of the epiphytic community on the saltmarsh cordgrass Spartina alterniflora. Hourly measurements of solar radiation and light attenuation (a function of plant canopy and tidal height) were used as forcing functions in the model. Steeper initial slopes (α) of photosynthesis vs. irradiance curves (P-I curves) were estimated in the summer (when the canopy was densest), indicating highest shade adaptation. Model validation showed a good agreement between actual hourly production measurements and hourly predicted net production (r² = 0.90). Predicted areal epiphytic community production was negative during all seasons and higher in the high marsh (short S. alterniflora zone) than in the low marsh (tall S. alterniflora zone), due to a more open canopy and less exposure to tidal waters. The results indicated that the epiphytic community on S. alterniflora in North Inlet is an energy sink (i.e. net heterotrophic community). When irradiance values were held constant at 615 µmol photons m^–2 s^–1 (mean daily irradiance value during daylight), production values were overestimated by 11.68 to 34.77%. Therefore, building quantitative models that include hourly changes in light is key to the realistic estimation of epiphytic production in salt marshes.

KEY WORDS: Epiphytic community production · Mathematical modeling · P-I curves · Salt marsh · Spartina alterniflora