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.