Paper Reviewed
Jothiramshekar, S., Benjamin, J.J., Krishnasamy, R., Pal, A.K., George, S., Swaminathan, R. and Parida, A.K. 2018. Responses of selected C3 and C4 halophytes to elevated CO2 concentration under salinity. Current Science 115: 129-135.

Soil salinity is a major stress that affects the growth and productivity of plants. Approximately 7 percent of the total global land area is affected by saline soils, while some 20-50 percent of global irrigated farmland operates under such conditions.

One of the more common consequences of high salt concentrations on plant growth is a reduction in plant water uptake, which often results in water stress. In contrast, elevated levels of atmospheric CO2 have been shown to reduce water stress by decreasing plant transpiration. The net result of these two opposing forces was the subject of examination in a recent paper published by Jothiramshekar et al. (2018). As their contribution to this topic, the seven Indian researchers studied the combined effects of elevated CO2 and salinity on the photosynthetic pigment content, lipid peroxidation level, electrolytic leakage and osmolyte concentration of two halophytes-Sesuvium portulacastrum, a plant which follows the C3 pathway for photosynthesis, and Suaeda nudiflora, which follows the C4 photosynthetic pathway. Both species are salt-tolerant halophytes.

The work was conducted at the mini-free air CO2 enrichment facility at the M.S. Swaminathan Research Foundation in Chennai, India. Plants were cultured hydroponically under either ambient (380 ppm) or elevated (500 ppm during daylight hours only) CO2 concentrations and normal or salt-stressed (200 mM NaCl added) conditions over a three-month period. At regular intervals, both during and at the end of the experiment, the authors made several measurements of the effect of CO2 and salt stress on the plants' growth. And what did they thereby learn?

Their results indicated that the small +120 ppm enrichment of CO2 during daylight hours only was significant enough to ameliorate the effects of salt in both plant species. More specifically, elevated CO2 improved plant chlorophyll content and reduced lipid peroxidation, electrical conductivity and total soluble sugars, which changes, according to Jothiramshekar et al., indicate that "elevated CO2 concentration is effective in offsetting physiological damages due to salinity stress in the plants studied." Consequently, the researchers conclude that halophytes (salt-tolerant species) "may benefit from rising atmospheric CO2 concentration."