Duckweeds under salt stress: a meta-analysis of growth inhibition in relation to morphological and physiological traits and a systematic review of molecular responses.

Salinity is one of the main environmental factors limiting the performance of duckweeds and despite growing ecological and biotechnological interest in these macrophytes, there is a lack of quantitative analyses of their responses to sodium chloride. To address this gap, we conducted a meta-analysis and a systematic review of 38 articles to quantify the effects of NaCl on growth, photosynthetic pigments, carbohydrate metabolism, osmotic adjustment, ionic homeostasis, oxidative stress, antioxidant defense and molecular responses in duckweeds. NaCl consistently reduced growth-related traits and photosynthetic pigments while increasing proline, oxidative stress, Na+ accumulation, K+ depletion and altered starch metabolism. Antioxidant responses varied among enzymes, with SOD, APX, GPX and GR generally showing positive responses under saline conditions. Species-specific analyses identified Spirodela polyrhiza and Lemna minor as having greater bioenergetic potential, whereas S. polyrhiza and Landoltia punctata showed lower ionic disturbances and stronger osmoprotective responses. Available molecular studies indicate the involvement of ABA-, ROS- and Ca2+-mediated signaling pathways, and individual studies highlight Ca2+ and K+ supplementation as promising strategies to enhance salt tolerance. Overall, duckweed salinity tolerance emerges from the coordinated interaction of ionic, osmotic and redox regulation, providing a mechanistic framework for future applications in saline environments and biomass-based technologies.