Elevated CO2 Alters the Physiological and Transcriptome Responses of Pinus densiflora to Long-Term CO2 Exposure

Physiological response and transcriptome changes were observed to investigate the effects on the growth, metabolism and genetic changes of Pinus densiflora grown for a long time in an environment with an elevated atmospheric CO2 concentration. Pine trees were grown at ambient (400 ppm) and elevated (560 ppm and 720 ppm) CO2 concentrations for 10 years in open-top chambers. The content of nonstructural carbohydrates was significantly increased in elevated CO2. It was notable that the contents of chlorophylls significantly decreased at an elevated CO2. The activities of antioxidants were significantly increased at an elevated CO2 concentration of 720 ppm. We analyzed the differences in the transcriptomes of Pinus densiflora at ambient and elevated CO2 concentrations and elucidated the functions of the differentially expressed genes (DEGs). RNA-Seq analysis identified 2415 and 4462 DEGs between an ambient and elevated CO2 concentrations of 560 ppm and 720 ppm, respectively. Genes related to glycolysis/gluconeogenesis and starch/sucrose metabolism were unchanged or decreased at an elevated CO2 concentration of 560 ppm and tended to increase at an elevated CO2 concentration of 720 ppm. It was confirmed that the expression levels of genes related to photosynthesis and antioxidants were increased at an elevated CO2 concentration of 720 ppm.