期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2012
卷号：109
期号：45
页码：E3094-E3100
DOI：10.1073/pnas.1216012109
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Dissolution of anthropogenic CO2 increases the partial pressure of CO2 (pCO2) and decreases the pH of seawater. The rate of Fe uptake by the dominant N2-fixing cyanobacterium Trichodesmium declines as pH decreases in metal-buffered medium. The slower Fe-uptake rate at low pH results from changes in Fe chemistry and not from a physiological response of the organism. Contrary to previous observations in nutrient-replete media, increasing pCO2/decreasing pH causes a decrease in the rates of N2 fixation and growth in Trichodesmium under low-Fe conditions. This result was obtained even though the bioavailability of Fe was maintained at a constant level by increasing the total Fe concentration at low pH. Short-term experiments in which pCO2 and pH were varied independently showed that the decrease in N2 fixation is caused by decreasing pH rather than by increasing pCO2 and corresponds to a lower efficiency of the nitrogenase enzyme. To compensate partially for the loss of N2 fixation efficiency at low pH, Trichodesmium synthesizes additional nitrogenase. This increase comes partly at the cost of down-regulation of Fe-containing photosynthetic proteins. Our results show that although increasing pCO2 often is beneficial to photosynthetic marine organisms, the concurrent decreasing pH can affect primary producers negatively. Such negative effects can occur both through chemical mechanisms, such as the bioavailability of key nutrients like Fe, and through biological mechanisms, as shown by the decrease in N2 fixation in Fe-limited Trichodesmium.
关键词：climate change ; cyanobacteria ; iron limitation
