Photosynthetic response of Myriophyllum salsugineum A.E. orchard to photon irradiance, temperature and external free CO 2

Abstract

The photosynthetic capacity of Myriophyllum salsugineum A.E. Orchard was measured, using plants collected from Lake Wendouree, Ballarat, Victoria and grown subsequently in a glasshouse pond at Griffith, New South Wales. At pH 7.00, under conditions of constant total alkalinity of 1.0 meq dm −3 and saturating photon irradiance, the temperature optimum was found to be 30–35°C with rates of 140 μmol mg −1 chlorophyll a h −1 for oxygen production and 149 μmol mg −1 chlorophyll a h −1 for consumption of CO 2. These rates are generally higher than those measured by other workers for the noxious Eurasian water milfoil, Myriophyllum spicatum L., of which Myriophyllum salsugineum is a close relative. The light-compensation point and the photon irradiance required to saturate photosynthetic oxygen production were exponentially dependent on water temperature. Over the temperature range 15–35°C the light-compensation point increased from 2.4 to 16.9 μmol (PAR) m −2 s −1 for oxygen production while saturation photon irradiance increased from 41.5 to 138 μmol (PAR) m −2 s −1 for oxygen production and from 42.0 to 174 μmol (PAR) m −2 s −1 for CO 2 consumption. Respiration rates increased from 27.1 to 112.3 μmol (oxygen consumed) g −1 dry weight h −1 as temperature was increased from 15 to 35°C. The optimum temperature for productivity is 30°C.