<b>Inverse responses of above- and belowground trait dissimilarity reduced competition intensity in trees</b>

Competition drives plastic responses of multiple traits in plants, dynamically altering interspecific trait dissimilarity and subsequently reshaping competition intensity. Yet the directionality of trait dissimilarity changes and their effects on competition are unclear. Using a three-year greenhouse experiment with 5,818 tree seedlings of seven species grown with and without interspecific competition, we revealed opposing competition-induced responses between above- and belowground multidimensional trait spaces: species similar in aboveground traits while diverging markedly belowground. Although contrasting, both responses significantly reduced competition intensity. These findings demonstrate a dynamic feedback loop between competition and trait expression through coordinated shifts across multiple traits, and suggest complementary above- and belowground trait adjustments could facilitate plant coexistence by reducing interspecific competition.