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Effects of salinity on photosynthesis and respiration of the seagrass Zostera japonica: A comparison of two established populations in North America
Shafer, D., J. E. KALDY, III, T. Sherman, AND K. Marco. Effects of salinity on photosynthesis and respiration of the seagrass Zostera japonica: A comparison of two established populations in North America. AQUATIC BOTANY. Elsevier Science Ltd, New York, NY, 95:214-220, (2011).
Zostera japonica is a non-native seagrass along the Pacific Coast of North America that is distributed from Northern California, USA to British Columbia, Canada.
Zostera japonica is a non-native seagrass along the Pacific Coast of North America that is distributed from Northern California, USA to British Columbia, Canada. Recent observations indicate that the species is expanding both latitudinally and into areas of lower salinity. There is insufficient ecophysiological data on Z. japonica to predict the potential for establishment and spread of the species. Our objective was to evaluate the photosynthetic response of two Z. japonica populations located near the northern and southern limits of distribution exposed to a range of salinities. Plants were collected from Padilla Bay, WA and Coos Bay, OR 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 the light saturated photosynthesis (Pmax) or dark respiration (Rd). For the Padilla Bay population, Pmax ranged from 192-390 µmols O2 gdw-1 h-1; for the Coos Bay population Pmax ranged from 226-774 µmols O2 gdw-1 h-1. Salinity had a significant effect on Pmax of the Coos population (p = 0.044) but not the Padilla population (p = 0.983). There were significant differences in leaf tissue Rd among salinity levels 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 Pmax rates at a salinity of 20. Additionally, this work suggests that southern populations may possess greater ecological ‘fitness’, particularly with respect to further expansion southward along the Pacific Coast and changes associated with global climate change.