The C4 Atriplex halimus vs. the C3 Atriplex hortensis: Similarities and Differences in the Salinity Stress Response

Abstract

Soil properties and the ability to sustain agricultural production are seriously impaired by salinity. The cultivation of halophytes is seen as a solution to cope with the problem. In this framework, a greenhouse pot experiment was set up to assess salinity response in the perennial C4 species Atriplex halimus, and in the following three cultivars of the annual C3 Atriplex hortensis: green, red, and scarlet. The four genotypes were grown for 35 days with water salinity (WS) ranging from 0 to 360 mM NaCl. Plant height and fresh weight (FW) increased at 360 vs. 0 WS. The stomatal conductance (GS) and transpiration rate (E) were more severely affected by salinity in the C4 A. halimus than in the C3 species A. hortensis. This was reflected in a lower leaf water potential indicating stronger osmotic adjustment, and a higher relative water content associated with more turgid leaves, in A. halimus than A. hortensis. In a PCA including all the studied traits, the GS and E negatively correlated to the FW, which, in turn, positively correlated with Na concentration and intrinsic water use efficiency (iWUE), indicating that reduced gas exchange associated with Na accumulation contributed to sustain iWUE under salinity. Finally, FTIR spectroscopy showed a reduced amount of pectin, lignin, and cellulose under salinity, indicating a weakened cell wall structure. Overall, both species were remarkably adapted to salinity: From an agronomic perspective, the opposite strategies of longer vs. faster soil coverage, involved by the perennial A. halimus vs. the annual A. hortensis cv. scarlet, are viable natural remedies for revegetating marginal saline soils and increasing soil organic carbon.

A meta‐analysis highlights the cross‐resistance of plants to drought and salt stresses from physiological, biochemical, and growth levels

“…Simultaneously, the decrease in OP of C 4 plants was greater than that of C 3 plants (Figure 2), as confirmed by previous studies (Barker et al, 1993;Calone et al, 2021b).…”

“…Correspondingly, due to the inevitable water loss during gas exchange, the RWC and WP of C 4 plants decreased more than those of C 3 plants under drought, salt, and combined stresses. Simultaneously, the decrease in OP of C 4 plants was greater than that of C 3 plants (Figure 2), as confirmed by previous studies (Barker et al, 1993; Calone et al, 2021b).…”

Atriplex (Atriplex halimus): Distribution, Morphology, Physiological Tolerance to Salinity and Drought: A Review

“…The interest in plants with high tolerability of salinity and arid conditions increased as the world population increased to meet the food increased requirements and finding plant species that help in alleviating desertification, especially in countries with dry climate and saline soils (Calone, Cellini, et al, 2021;Habib et al, 2016). The concern in Atriplex halimus was initiated as part of the solution of soil salinity and arid conditions in different countries.…”

“…The Atriplex halimus species grows in low annual rainfall in winter and high temperatures in summer with high potential evapotranspiration (Calone, Cellini, et al, 2021). The soils of these areas are characterized as alkaline soils with pH values ranging from 7 to 11 (David J. .…”

“…Most of the world's efforts are concentrated on finding new resistant species that tolerate the newly initiated conditions (Calone, Bregaglio, et al, 2021). The concern was related to the study of the morphology of Atriplex halimus to figure out the mechanism this plant behaves under different conditions (Calone, Cellini, et al, 2021). This concern is also the result of the contribution of Atriplex halimus in food security that helps in fighting starvation around the world (Petropoulos et al, 2018).…”