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General Marine Environmental Science
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Thermal plasticity of nitrogenase activity in Trichodesmium erythraeum IMS 101
P-GS-12-S
Xiangqi Yi* , Xiamen University
Kunshan Gao, Xiamen University
Presenter Email: yixiangqi0415@126.com |
| The cyanobacterium Trichodesmium is one of the most significant N2-fixing organisms in the tropical and subtropical oceans and plays an important role in the biogeochemical cycles of nitrogen and carbon. Understanding its response to ongoing global warming is one of the keys to predict the potential effects of climate change on marine ecosystems. Here, we show that the optimum temperature of growth is 27 oC in Trichodesmium erythraeum IMS 101, and warming (+4 oC inhibits its growth. However, this thermal effect on growth disappears when growth is limited by light intensity, that is, growth rates of populations grown under 23, 27 and 31 oC are similar at limiting light intensity. This suggests that compared to temperature, light is the primary limiting factor which may cover the effect of temperature on Trichodesmium's growth. We also explore the thermal plasticity of nitrogenase activity in Trichodesmium. It is remarkable that the optimum temperatures (Topt) of nitrogenase activity are hardly affected by either growth temperature or growth light intensity except for populations cultured at 31 oC and limiting light intensity whose Topt is about 27 oC, 2 oC lower than those of other populations. The double pressures of warming and light-limitation severely inhibit the performance of nitrogenase activity at high measuring temperature. The activation energy (Ea) of nitrogenase activity, reflecting the thermal sensitivity when measuring temperature is below the optimum temperature, is affected by growth temperature. The nitrogenase activities of high-temperature grown populations are more sensitive than those of low-temperature grown populations. Surprisingly, Ea is not affected by growth light intensity. Further exploration suggests that this should be one of the results of acclimation, because for the same population, Ea is higher when measured at saturating light intensity than at limiting light intensity. The deactivation energy (Eh) of nitrogenase activity, reflecting the decreasing rate when measuring temperature is above the optimum temperature, is lower for populations grown under warming conditions regardless the light intensity, helping the warming-acclimation populations maintain nitrogenase activity at high temperature. However, all in all, it seems that the thermal plasticity of nitrogenase activity gives not much advantages of acclimating to high temperature in Trichodesmium, which may constrain its adaptation to global warming. |
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