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EPA Researchers Co-author Most Downloaded Aquatic Botany Article

An article written by James E. Kaldy and Katharine M. Marko, researchers at NHEERL’s Western Ecology Division (WED), along with Deborah J. Shafer and Timothy D. Sherman, is among the 25 most downloaded Aquatic Botany articles in the past 90 days. “Effects of salinity on photosynthesis and respiration of the seagrass Zostera japonica: A comparison of two established populations in North America,” published in October 2011, is abstracted below.

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, WA (northern), and Coos Bay, OR (southern), and cultured together in experimental tanks at three 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 (Pmax) or dark respiration (Rd). For the Padilla Bay population, Pmax ranged from 192 to 390?mol O2 gDW?1h?1; for the Coos Bay population, Pmax ranged from 226 to 774?mol O2 gDW?1h?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 Rd 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 Pmax 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.

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