Potassium (K) availability in plant cells is critical for maintaining plant productivity across many terrestrial ecosystems. Yet, there is no comprehensive assessment of the mechanisms by which plants respond to potassium application in such conditions, despite the global challenge of escalating osmotic stress. Herein, we conducted a meta-analysis using data from 2381 paired observations to investigate plant responses to potassium application across various morphological, physiological, and biochemical parameters under both osmotic and nonosmotic stress. Globally, our results showed the significant effectiveness of potassium application in promoting plant productivity (e.g. +12%~30% in total dry weight), elevating photosynthesis (+12%~30%), and alleviating osmotic damage (e.g. −19%~26% in malonaldehyde), particularly under osmotic stress. Moreover, we found evidence of interactive effects between osmotic stress and potassium on plant traits, which were more pronounced under drought than salt stress, and more evident in C₃ than C₄ plants. Our synthesis verifies a global potassium control over osmotic stress, and further offers valuable insights into its management and utilization in agriculture and restoration efforts.

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