Effects of salt stress on the growth and physiological characteristics of Phyla canescens

Soil salinization is a major roadblock restricting agricultural production and ecological restoration work along China’s coastal areas. To work out the salt-adaptive physiological mechanism of Phyla canescens (a perennial groundcover that holds great potential for saline land remediation) we set seven NaCl concentration gradients for testing: 0 mM (0%, blank control), 34.2 mM (0.2%), 68.4 mM (0.4%), 102.7 mM (0.6%), 136.9 mM (0.8%), 171.1 mM (1.0%), and 256.7 mM (1.5%). After 30 days of continuous salt treatment, we measured two major types of indicators: plant growth traits (plant height, branch count, underground and aboveground fresh weight & dry weight) and physiological indices (antioxidant enzyme activity, osmotic adjustment substances, cell damage markers, chlorophyll content). The test results show a clear rule: as NaCl concentration goes up, plant height and branch number drop steadily. Aboveground and underground biomass both rise first and then fall, hitting the maximum value under 0.2% NaCl treatment. The activity levels of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) all climb within mild to moderate salinity and slide down when salt concentration gets too high. Meanwhile, proline, soluble sugar, malondialdehyde (MDA) and leaf relative conductivity keep rising along with salt content, which tells us osmotic stress and membrane lipid peroxidation keep getting worse. Chlorophyll a, chlorophyll b and total chlorophyll all decrease significantly as salinity increases, and chlorophyll b reacts far more sensitively to salt damage than chlorophyll a. Low-concentration NaCl (0.2% ∼ 0.4%) can boost vegetative growth of P. canescens . Once salt concentration exceeds 0.6%, growth gets obviously held back, and the survival rate drops to only 46.67% under 1.5% NaCl. Combining survival performance and physiological response data, we confirm P. canescens has strong salt tolerance, and it can serve as the core groundcover plant for greening mildly and moderately saline land.