Despite the important role of root exudates in the functions and processes of forest ecosystems, few studies have examined the effects of warming on the chemical composition of root exudates. In this study, we examined how warming affected composition of fine root exudates of Chinese fir (Cunninghamia lanceolata) saplings in different seasons. We designed a complete randomized block design soil warming (+ 4 ℃) experiment. Through liquid chromatography-mass spectrometry (LC/MS) in combination with a modified culture-based cuvette system, we compared metabolite composition of root exudates between warmed and control saplings. Warming changed the concentration of more metabolites in the summer than the spring. More primary metabolites (e.g., amino acids and organic acids) and defense-related secondary metabolites (e.g., phenols and terpenoids) significantly increased after warming in summer than in spring. Warming enhanced multiple metabolite pathways related to absorption of nutrients (e.g., alanine, aspartate, and glutamate metabolism for N and citrate cycle for P) and water (e.g., arginine biosynthesis) and plant defense (e.g., enhanced tryptophan metabolism in the spring, flavone, and flavonol biosynthesis in the summer). Warming increased the composition and pathways of metabolites in root exudates of Chinese fir saplings. The alternation was much more pronounced in the dry summer suggesting that changes in metabolite composition and pathways are important responses of Chinese fir saplings to drought. These findings provide insights into how climate change may affect important belowground processes in subtropical forests.
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