Integrating phenotypic and molecular approaches to unravel salinity and cold tolerance in wetland plants for ecosystem restoration

Abstract

Wetland salinization represents a significant global environmental challenge, threatening the viability and stability of both plant communities and ecosystems. There are few studies focused on species selection for the restoration of saline wetlands, specifically studies that integrate plant functional traits and molecular mechanisms. Juncus articulatus and Paspalum vaginatum, common perennial herbaceous species in freshwater or saline wetlands, are considered potential candidates for the restoration of saline wetlands. This study assessed phenotypic and physiological disparities in salt and cold tolerance and further employed an integrated transcriptomic and metabolomic approach to comprehensively elucidate the underlying mechanisms of cold tolerance. Under salinity treatments (400 mM NaCl for 5 days followed by 700 mM NaCl for 7 days with uniform irrigation), the survival rate of P. vaginatum reached 87.76 %. P. vaginatum exhibited significantly greater plant height and salt tolerance compared to J. articulatus. It also demonstrated higher proline content and elevated activities of SOD, POD, APX, ASA, and GSH. Additionally, Pn, Fv/Fm, and enzyme activities related to sucrose metabolism were significantly higher. Notably, under 700 mM NaCl salt conditions, P. vaginatum maintained significantly lower Na⁺ concentrations and higher K⁺/Na⁺ ratios in its leaves, as well as higher K⁺ concentrations and K⁺/Na⁺ ratios in its roots. J. articulatus possessed an extensive root system and exhibited significantly higher cold tolerance. After exposure to natural cold conditions during winter, with a minimum ground temperature of-6.5°C for 5 days, the plants exhibited markedly higher proline content and significantly higher activities of SOD, CAT, APX, and GSH. Although Pn exhibited a declining trend, it remained significantly higher than P. vaginatum. Cold stress induced significant transcription-associated metabolomic alterations in J. articulatus, enhancing cold tolerance through upregulated metabolic pathways including glutathione, starch and sucrose, and flavonoid biosynthesis. Under cold stress, it augmented its antioxidant defense by escalating glutathione synthesis and its precursors, L-Glutamate and NADP⁺. Meanwhile, it upregulated sucrose and trehalose levels and significantly increased activities of SS, SPS, and FBPase, which enhanced cold tolerance through the accumulation of soluble sugars. These findings provide valuable insights into the adaptive mechanisms of J. articulatus and P. vaginatum, offering crucial guidance for selecting resilient species in the restoration of saline and cold-affected wetlands.