Primary metabolites in root exudates are not affected by long‐term soil warming in a temperate forest

Abstract Primary metabolites in root exudates are essential for plant nutrition and rhizosphere microbiome function, potentially responding sensitively to climate warming. However, the effects of long‐term soil warming on exudate metabolites in forests remain unclear. We investigated how long‐term soil warming (>14 years, +4°C) in a temperate mountain forest in Austria affects the root exudation rates and profiles of primary metabolites in Picea abies (Norway spruce), the dominant tree species at the site and explored how strongly root exudate rates are controlled by root tissue metabolism. We used targeted metabolite quantification to measure three major groups of primary metabolites—sugars, amino acids and organic acids—in root exudates and tissues. Root exudation rates and profiles of primary metabolites showed no response to long‐term soil warming, though sampling date had significant effects. Primary metabolites in root tissues and in root exudates showed largely overlapping compositional patterns, and their concentrations were strongly positively correlated, suggesting that root tissue metabolism plays a central role in controlling exudate composition and rate. Our findings show that woody plant roots maintained metabolically stable exudation profiles under long‐term soil warming, as supported by the absence of warming effects on exudates across years and seasons, despite independent measurements at the same site reporting pronounced increases in fine root growth and respiration. Together, these results indicate a warming‐induced reallocation of root carbon away from exudation and towards structural and metabolic investment, highlighting the complexity and prioritization of carbon use strategies under climate change. Read the free Plain Language Summary for this article on the Journal blog.