Divergent metabolic responses of Picea schrenkiana and Larix sibirica to a drought gradient revealed by tree-ring metabolomics

Objective  Tree-ring width and stable isotopes have revealed differential drought responses between Picea schrenkiana and Larix sibirica in the eastern Tianshan Mountains. These approaches, however, capture macroscopic outcomes of growth and water use, and thus fall short of resolving species-specific metabolic adjustments under varying drought intensities. To address this gap, we compared the two species across drought gradients, with emphasis on changes in differential metabolite abundance and key pathway responses.

Methods We selected Picea schrenkiana and Larix sibirica as the study species. Drought intensities were classified using runs theory applied to the self-calibrating Palmer Drought Severity Index (scPDSI). Metabolites from tree-ring samples were profiled via untargeted metabolomics and identified through database matching. We then screened differential metabolites by multivariate statistical analysis and mapped them to KEGG pathways.

Results The two species exhibited opposite metabolic trajectories as drought intensity increased. (1) From mild to moderate drought, the number of differential metabolites in Picea schrenkiana increased from 330 to 513, whereas that in Larix sibirica fell from 1182 to 220. (2) Under mild drought, both species enriched the flavonoid biosynthesis pathway, yet their metabolite accumulation patterns diverged. Under moderate drought, Picea schrenkiana enriched the lignin biosynthesis pathway while suppressing the tryptophan metabolism pathway; Larix sibirica, by contrast, retained only the galactose metabolism pathway as a sustained response.

Conclusions The two species displayed distinct metabolic response patterns across the drought gradient. Picea schrenkiana strengthened its metabolic response with increasing drought severity, whereas Larix sibirica showed broad responses under mild drought but weakened ones under moderate drought. These findings highlight the divergent metabolic strategies of evergreen and deciduous conifers under varying drought intensities, and provide metabolic-level evidence for understanding drought adaptation in coniferous species.