Comparative physiological and transcriptomic analyses reveal the mechanisms of CO(2) enrichment in promoting the growth and quality in Lactuca sativa

The increase in the concentration of CO(2) in the atmosphere has attracted widespread attention. To explore the effect of elevated CO(2) on lettuce growth and better understand the mechanism of elevated CO(2) in lettuce cultivation, 3 kinds of lettuce with 4 real leaves were selected and planted in a solar greenhouse. One week later, CO(2) was applied from 8:00 a.m. to 10:00 a.m. on sunny days for 30 days. The results showed that the growth potential of lettuce was enhanced under CO(2) enrichment. The content of vitamin C and chlorophyll in the three lettuce varieties increased, and the content of nitrate nitrogen decreased. The light saturation point and net photosynthetic rate of leaves increased, and the light compensation point decreased. Transcriptome analysis showed that there were 217 differentially expressed genes (DEGs) shared by the three varieties, among which 166 were upregulated, 44 were downregulated, and 7 DEGs were inconsistent in the three materials. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that these DEGs involved mainly the ethylene signaling pathway, jasmonic acid signaling pathway, porphyrin and chlorophyll metabolism pathway, starch and sucrose metabolism pathway, etc. Forty-one DEGs in response to CO(2) enrichment were screened out by Gene Ontology (GO) analysis, and the biological processes involved were consistent with KEGG analysis. which suggested that the growth and nutritional quality of lettuce could be improved by increasing the enzyme activity and gene expression levels of photosynthesis, hormone signaling and carbohydrate metabolism. The results laid a theoretical foundation for lettuce cultivation in solar greenhouses and the application of CO(2) fertilization technology.