Potassium: a neglected nutrient in global change

Aim Potassium ( K ) is the second most abundant nutrient in plant photosynthetic tissues after nitrogen ( N ). Thousands of physiological and metabolic studies in recent decades have established the fundamental role of K in plant function, especially in water‐use efficiency and economy, and yet macroecological studies have mostly overlooked this nutrient. Methods We have reviewed available studies on the content, stoichiometry and roles of K in the soil–plant system and in terrestrial ecosystems. We have also reviewed the impacts of global change drivers on K content, stoichiometry and roles. Conclusions The current literature indicates that K , at a global level, is as limiting as N and phosphorus ( P ) for plant productivity in terrestrial ecosystems. Some degree of K limitation has been seen in up to 70% of all studied terrestrial ecosystems. However, in some areas atmospheric K deposition from human activities is greater than that from natural sources. We are far from understanding the K fluxes between the atmosphere and land, and the role of anthropogenic activities in these fluxes. The increasing aridity expected in wide areas of the world makes K more critical through its role in water‐use efficiency. N deposition exerts a strong impact on the ecosystem K cycle, decreasing K availability and increasing K limitation. Plant invasive success is enhanced by higher soil K availability, especially in environments without strong abiotic stresses. The impacts of other drivers of global change, such as increasing atmospheric CO 2 or changes in land use, remain to be elucidated. Current models of the responses of ecosystems and carbon storage to projected global climatic and atmospheric changes are now starting to consider N and P , but they should also consider K , mostly in arid and semi‐arid ecosystems.