Elevated CO2 leads to carbon sequestration by modulating C4 photosynthesis pathway enzyme (PPDK) in Suaeda monoica and S. fruticosa

The C4 halophytic species Suaeda monoica and S. fruticosa, possess the C4 photosynthesis pathway without Kranz anatomy were grown at ambient (470 ppm CO2) and elevated (850 ppm CO2) atmospheric CO2 under control containment facility to study the plant response under CO2 stress condition. The relative growth of both Suaeda species was enhanced with atmospheric CO2 enrichment compared to control (ambient) condition. The photosynthesis rate was found 2.5 μmol CO2 m− 2 s− 1 in both species under stress condition compared to about 1.9 μmol CO2 m− 2 s− 1 under control conditions. About 0.3 mol H2O m− 2 s− 1 conductance was detected under an unstressed condition which decreased significantly to ~ 0.07 mol H2O m− 2 s− 1 on the 6th day of stress treatment. Similarly, transpiration rate was also decreased significantly from 4.4-5.2 mmol H2O m− 2 s− 1 to 1.7-1.9 under stress condition. In contrast, VpdL increased significantly from 1.9 kPa to 2.5 kPa under stress condition. A higher total chlorophyll content observed in S. monoica (56.36 mg g− 1 tissue) compared to S. fruticosa (33.12 mg g− 1 tissue) under unstressed (control) condition. A significant increase was found in the total chlorophyll content of S. fruticosa (45.47 mg g− 1 tissue) with stress treatment compared to control (33.12 mg g− 1 tissue). In contrast, the total chlorophyll decreased in S. monoica (51.58 mg g− 1 tissue) under similar stress condition compared to control plants (56.36 mg g− 1 tissue). About 6-6.8 mg total sugar per gram tissue found under control condition which enhanced further (7.5 to 11 mg g− 1 tissue) under stress condition. Similarly, total reducing sugar (~ 2 mg g− 1 tissue) and total starch content (6.5-11 mg g− 1 tissue) increased under stress condition. About 6.5- and 3- fold higher expression of PPDK gene was observed for S. monoica and S. fruticosa, respectively under CO2 stress condition. PPDK (1.2- and 1.5- fold) and antioxidant enzymes; APX (12.7- and two-fold), CAT (2.2- and 6.4- fold) and SOD (4.6- and 94- fold) enhanced significantly in S. fruticosa and S. monoica, respectively under high CO2 stress condition compared to control plants. Overall, it was observed that PPDK enzyme plays a key role in C4 photosynthesis pathway and S. monoica is a potential candidate to be explored further for the saline agricultural and CO2 capture.