The stoichiometric decoupling of leaf Ca to K and Mg is driven by their differential responses to climate

Global climate change has intensified extreme heat and drought events worldwide. Leaf potassium (K), calcium (Ca) and magnesium (Mg) are critical for maintaining plant physiological functions and stress resistance. However, the large-scale distributions, stoichiometric relationships and future climate-change dynamics of these three elements in plants remain unclear. Here, we explored the spatial and temporal variations in leaf K/Ca/Mg concentration and their stoichiometry of woody angiosperm plants in China, and the underlying potential drivers, based on climate and soil variables and CMIP6 future climate data. We found that leaf K and Mg concentrations increased from south-eastern to north-western China, primarily regulated by precipitation, with soil showing limited contribution. Leaf Ca peaked in central China and showed a unimodal relationship with temperature and precipitation, with drought and cold reducing Ca uptake by limiting transpiration. Leaf K and Mg were strongly coupled across China, whereas Ca was coupled with them only in humid and warm regions but became decoupled in arid and cold regions. Under future climate, scenario-based projections suggested that the overall patterns and relationships of leaf K-Ca-Mg may remain similar to current ones, while leaf Ca concentration may increase and become increasingly decoupled from leaf Mg. These findings contribute to our understanding of the nutrient-adaptive strategies of woody plants and provide critical insights for evaluating potential changes in nutrient cycling and forest productivity under global change.