Physiological And Molecular Responses Of The Green Algae Chlorella Variabilis To Long-term And Short-term Elevated CO₂

Chlorella variabilis are the main primary producers in water because they have an efficient photosynthesis mechanism.However this mechanism is particularly sensitive to elevated CO₂.There have been a considerable number of studies on the effect of short-term acidification on C.variabilis.However,there is no information on long-term adaptive responses.To investigate the response of C.variabilis when exposed to increased CO₂ concentration,physiological and transcriptome analyses were carried out on C.variabilis that had been cultivated at 1,000 ppm CO₂ for long?LT?and short?ST?periods of time and these were compared with samples from the control group?CK?.We combined transcriptomic information with physiological results from C.variabilis in an attempt to predict and unravel the foundation of the reaction mechanisms used by C.variabilis when it adapts to long-term and short-term elevated CO₂ conditions.The main result of study is as follows:The common responses of the ST and LT C.variabilis included increased pigment levels,and higher F_v/F_m efficiency and carbon fixation rate.The results indicated that current CO₂ levels could limit C.variabilis growth and photosynthesis.Furthermore,CO₂ addition lowered the carbohydrate contents This may be a response to the change in the cultivation environment.We concluded that elevated CO₂ conditions indicated that the carbon from intracellular carbohydrate stores was directed to synthesis other nutritional compostition.The resulted showed that enriching CO₂ to 1000 ppm resulted in insignificant changes to C/N in C.variabilis.It is known that the genes involved in nitrogen and carbon metabolism are often co-regulated when environmental conditions change,which means that algae can co-adjust and reach a dynamic equilibrium.However,there was a distinct disparity between LT and ST,such as higher contents of total lipid,soluble protein and fatty acid in ST,the C.variabilis which cultivated at 1000ppm for long term failed to evolve specific adaptions.Transcriptome changes in the ST samples were coincident with the observed physiological responses,which suggested that carbon flow to the acetyl-CoA pool from photosynthetic enhanced the production of lipids and fatty acids.This was confirmed by the depressed glycolysis and?-oxidation levels,upregulation of fatty acids and triglyceride synthesis pathways,lower soluble carbohydrate contents,and lipid accumulation.However,we found no change or the downregulation of genes involved in cellular metabolism in the LT samples,such as the genes participating in protein,fatty acid,and triglyceride synthesis.The results demonstrated that C.variabilis are generally sensitive to the ST condition,but hardly responded to the LT treatment and failed to evolve any specific adaptations.In this study,we analyzed the response of C.variabilis to a likely future environment of elevated pCO₂?1000 ppm?.Short term acidification induced trophic component accumulation,While long-term acidification promoted the growth of C.variabilis,there was no significant change in other results.The transcriptome analysis support a theoretical foundation to explain the physiological response of C.variabilis to elevated pCO₂.