Effects of salinity on photosynthesis and respiration of the seagrass Zostera japonica: A comparison of two established populations in North America

Authors

Deborah J. Shafer, US Army Corps of Engineers
James E. Kaldy, US EPA, Western Ecology DivisionFollow
Timothy D. Sherman, University of South Alabama
Katharine M. Marko, US EPA, Western Ecology Division

Date of this Version

2011

Citation

Aquatic Botany 95 (2011) 214– 220; doi:10.1016/j.aquabot.2011.06.003

Abstract

Photosynthetic responses were quantified for two Zostera japonica Aschers, and Graebn. populations from the northern and southern limits of distribution exposed to a range of salinities along the Pacific Coast of North America. Plants were collected from Padilla Bay, Washington (northern) and Coos Bay, Oregon, USA (southern) and cultured together in experimental tanks at 3 salinities (5, 20 and 35) under saturating irradiance for 3 weeks. Subsequently, photosynthesis–irradiance (P vs. E curves) relationships for leaf segments from the two populations were assessed using an oxygen electrode system. We found no evidence for diel rhythms in either light saturated photosynthesis (P_max) or dark respiration (R_d). For the Padilla Bay population, P_max ranged from 192 to 390 µmol O₂ g DW⁻¹ h⁻¹; for the Coos Bay population P_max ranged from 226 to 774 µmol O2 g DW⁻¹ h⁻¹. Photosynthetic maxima of the Coos Bay plants occurred at a salinity of 20, whereas salinity had no effect on the photosynthetic maxima of the Padilla Bay plants. There were significant differences in leaf tissue R_d among salinity treatments but the two populations responded similarly to salinity. North American populations of Z. japonica are best adapted to intermediate salinities, displaying minimum Rd rates, lower compensation irradiance, higher saturation irradiance, and greater P_max rates at a salinity of 20. Additionally, the southern population may be better adapted to southward expansion along the Pacific Coast and changes associated with global climate change.