The marine diatom Thalassiosira pseudonana was grown in a continuous culture system to study the interactive effects of temperature, irradiance, nutrient limitation, and the partial pressure of CO2 (pCO2) on its growth and physiological characteristics. The cells were able to grow at all combinations of low and high irradiance (50 and 300 mmol photons m−2 s−1, respectively), low and high pCO2 (400 and 1000 ppmv, respectively), nutrient limitation (nitrate-limited and nutrient-replete conditions), and temperatures of 10–30°C. At 5°C and 32°C, the cells were able to grow only at high irradiance. Increasing the pCO2 from 400 to 1000 ppmv increased growth rates only when other conditions were optimal, consistently increased productivity indices at high but not low irradiance, and increased carbon/chlorophyll a ratios under nutrient-replete conditions when temperatures were outside the optimal range of 20–25°C. Dark respiration rates were 25% of net growth rates under nutrient-replete conditions, but under nitrate limitation the percentage loss to dark respiration was higher and was positively correlated with temperature. Under nitrate-limited conditions losses to dark respiration were consistently higher at high versus low pCO2 when temperatures were suboptimal or supraoptimal. Increasing the pCO2 from 400 and 1000 ppmv presumably facilitated acquisition of inorganic carbon but was associated with a decrease of pH from 8.0 to 7.7 that may have been responsible for the adverse effects of elevated pCO2 when other conditions were suboptimal. The minimum quantum requirement for carbon fixation, however, remained constant (9.4 ± 0.3) across all growth conditions.
Dr. Edward Laws received his Ph.D in Chemical Physics from Harvard University in 1972. He was an instructor in the oceanography department at Florida State University from 1971 to 1974. He joined the faculty of the oceanography department at the University of Hawaii in 1974, where he became a professor of oceanography in 1984. He moved to Louisiana State University (LSU) in 2005 and served as the dean of the School of the Coast & Environment until 2008. He is currently a professor in the department of environment at Louisiana State University. Dr. Laws has published more than 200 refereed papers in scientific journals and is the author of two books, Mathematical Methods for Oceanographers and Aquatic Pollution. Aquatic Pollution is now in its 4th edition and has been translated into both Japanese and Chinese. Dr. Laws served on the editorial board of Limnology & Oceanography from 1981 to 1984. He received the Best Paper Award from the Organic Geochemistry Division of the Geochemical Society in 1995 and the Tyge Christensen Prize for best algal paper in Phycologia in 2007. He received the Qingdao Award from the Qingdao Municipal Government in 2012 and 2015, Friendship Award from Government of China in 2018 and delivered the Nanqiang Lecture “The Earth’s Changing Climate: Natural Cycles and Human Effects” at Xiamen University on July 23, 2013.