Effects Of Different Growth Conditions On Photo-physiological And Biochemical Characteristics Of Ulva Lactuca

The physiological and biochemical activities of macroalga are affected by many environmental factors.The concentration of CO₂ in the atmosphere,the temperature change in the environment and the nutrient concentration are several important environmental factors.At present,the physiological and biochemical characteristics of seaweeds have been reported in the case of increased CO₂ concentration,and there are many studies on the effects of different temperatures on macroalga.In addition,there are many results about the effect of nutrient concentration change on seaweed.While,most of the relevant researches just focus on the growth and other apparent parameters,the key photosynthetic physiological mechanism is little known.In this paper,we studied the photo-physiological characters of macroalga Ulva lactuca（collected from the intertidal zone of Nanao Island,Guangdong Province）,under different temperatures（15 ℃,20 ℃ and 25 ℃）,CO₂ concentrations（360 μL/L and 720 μL/L）and nutrient levels（N concentration of 10 μ mol / L and 200 μmol/L;P concentration of 40 μmol / L and 0.5 μmol/L）,based on chlorophyll fluorescence technique.By studying the change of photosynthesis system Ⅱ（PSⅡ）in U.lactuca under the interaction of above factors,we want to further reveal the impact of global climate change on this seaweed.The main findings are as follows:（1）The increases of CO₂,P and N nutrient concentration could promote the relative growth rate of U.lactuca at three temperatures,and also change the photosynthetic pigment content in macroalga.However,the effect of P nutrient on U.lactuca was not very significant,while the effects of the other two factors were significant.At the same time,high P nutrient could inhibit the activity of PSⅡ photo-reaction center of seaweed,and thus affected its photosynthesis.N nutrient not only promoted the the above apparent parameters of U.lactuca,but also improved the activity of PSⅡ photo-reaction system and increases its photosynthesis.Although the CO₂ enrichment group promoted the relative growth rate of U.lactuca,the increase of CO₂ concentration could cause the stress of the photo-reaction center of U.lactuca and inhibit the activity of light reaction center.（2）Temperature changes showed a greater impact on the U.lactuca.Under N nutrient enrichment,the medium temperature can promote the relative growth rate and pigment content of seaweed,beyond which these parameters were inhibited.At the same time,the photosynthetic parameters,such as ABS / RC and DIO / RC in PSⅡ reaction center were decreased,while Fv / Fo,Fraction of OEC,φPo and ETo / RC were significantly increased.Beyond the appropriate range,the elevated temperature could cause the opposite results.Under P nutrient enrichment,the increase or decrease of temperature had no significant effect on the apparent parameters of U.lactuca,and the trend of P nutrient enrichment group was similar to that in control group.CO₂ enrichment significantly reduced pigment content at 15 ℃,while promoted the relative growth rate of U.lactuca at 15 ℃-25 ℃.Within the temperature range of 15 ℃-25 ℃,reduced temperature could decrease the ABS/RC,DIO/RC and other parameters in photo-reaction center,under the increased temperature,the change of above parameters were opposite.While,Fv Fo,φEo,φPo,ETo/RC were significantly decreased in the CO₂ enrichment group at three levels of temperatures.In general,the effects of CO₂ concentration,temperature changes and nutrient interactions on the growth and photo-physiological and biochemical characteristics of seaweed were significant,but the effects were different.The chlorophyll fluorescence technique was used to analyze the photo-mechanism of above environmental factors on U.lactuca.These environmental factors affected the photosynthesis and growth of U.Lactuca via affecting the reaction center of PSⅡ...