Alfalfa (), an important leguminous forage crop, is valued for its high nutritional content, substantial yield, palatability, and broad adaptability. Drought is among the most significant environmental constraints on alfalfa growth, particularly in the karst regions of southwestern China. In this study, we conducted pot experiments to investigate the growth and physiological responses of seven alfalfa varieties introduced into the karst region of Guizhou under drought conditions. The results revealed that drought stress markedly reduced both plant height and aboveground biomass accumulation. Moreover, under drought stress, these alfalfa varieties exhibited increased root length, root surface area, and root tip number; elevated protective enzyme activities; and decreased levels of hydrogen peroxide (HO) and malondialdehyde (MDA), thereby maintaining relatively higher water content. Each of the seven varieties displayed distinct growth and physiological adaptation mechanisms under drought stress. Integrating principal component analysis and membership function analysis, we ranked the drought resistance of these alfalfa varieties from highest to lowest as follows: Crown > WL525 > Colosseo > Victoria > PANGO > Giant 801 > Dimitra. These findings provide valuable insights for introducing drought-resistant alfalfa varieties into karst regions of southwestern China and offer guidance for breeding and cultivation strategies across various environmental conditions.
