Reprint Series No. 22

THE EFFECT OF EXPOSURE TO ENVIRONMENTAL NORMOXIA AND HYPOXIA ON PHOTOSYNTHETIC RATE AND CHLOROPHYLL CONCENTRATION IN INTERTIDAL ZOSTERA MARINA LEAVES

Sharon R. Riggs

 

May 1995

Bibliographic Citation
Riggs, Sharon R. 1995. The effect of exposure to environmental normoxia and hypoxia on photosynthetic rate and chlorophyll concentration in intertidal Zostera marina leaves. Master of Science Thesis, Western Washington University, Bellingham, Washington. 74pp. Washington State Department of Ecology (Publication No. SWR-95-77), Padilla Bay National Estuarine Research Reserve Reprint Series No.22.

Abstract
Exposure of intertidal Zostera marina leaves to dark environmental normoxia or hypoxia significantly reduced photosynthetic rates but had little effect on chlorophyll concentrations in leaf tissue. A 2 x 3 factorial experiment was conducted at each of three temperatures: l0°, 20°. and 30°C. Photosynthetic rates were determined using a radioisotope method and leaf chlorophyll was extracted and measured spectrophotometrically.

Leaves exposed to normoxia in the dark at 10°C and at 30°C had significantly greater mean photosynthetic rates than leaves exposed to hypoxia in the dark. At 20°C there was a significant interaction between the factors oxygen and time. Time had a significant effect on photosynthetic rates for hypoxic treatments but was not significant for normoxic treatments. The photosynthetic rate means for leaves exposed to hypoxia were significantly lower than normoxic means for each time tested (24, 36 and 48 hours).

At 10°C and 20°C, mean chlorophyll concentrations in leaves exposed to normoxia or hypoxia in the dark were not significantly different. At 30°C mean chlorophyll a concentration in Z. marina leaves was significantly higher in leaves exposed to normoxia in the dark than for leaves exposed to hypoxia in the dark.

These results indicate that Zostera marina growing in estuaries that are prone to ponding or eutrophication may be impacted if conditions exist that encourage hypoxic conditions. Those conditions would include temperatures of 30°C or higher, decomposition of macroalgae in ponded sites, or prolonged exposure to the dark at 10°C, 20°C, or 30°C.