Six Rotation Years Drive Dynamic Shifts in Agronomic Traits, Photosynthesis, and Tuber Metabolomics of Dioscorea...

Background/Objectives:Dioscorea opposita Thunb. is widely cultivated as a nutritious crop; however, the dynamic effects of different rotation years on its agronomic traits, photosynthetic performance, and tuber metabolome remains poorly understood. This study aimed to systematically investigate the effects of varying rotation years on these parameters. Methods: Six field treatments were established: Y0 (0-year rotation, continuous cropping), Y1 (1-year), Y2 (2-year), Y3 (3-year), Y4 (4-year), and CK (fallow land with ≥8 years of rotation). Tuber metabolomic profiling was performed using UPLC-MS/MS. Results: Rotation years <4 showed no differences in tuber length or yield, with tuber length ranging from 35.42 to 47.18 cm and yield from 103.31 to 133.77 g. Shorter rotations (<4 years) exhibited significantly reduced chlorophyll content, as well as diminished photosynthetic parameters (Pn, Gs, and Tr). Metabolomic analysis identified 93 metabolites, of which 30 were differential, with 11 showing enrichment in Y4. Notably, procyanidin B1, kaempferol, dihydroquercetin, pyridoxine, and L-cystine exhibited higher levels in Y0. Sinapic acid, tyramine, glutamine, dibutyl phthalate, and fructose reached peak levels in fallow land (CK). All pairwise comparisons except Y4 vs. CK were enriched in the flavonoid and flavone biosynthesis pathway, with flavonoids representing the predominant class of differential metabolites. Cluster analysis showed that metabolites in clusters 1 and 7 peaked at Y4, while those in clusters 3, 4, 5, and 6 reached minimum levels at Y4. Conclusions: Rotation years of less than 4 years led to restricted growth, reduced yield, impaired chlorophyll synthesis, and altered metabolic profiles. A four-year rotation is identified as a critical turning point in metabolite accumulation, providing valuable guidance for sustainable D. opposita cultivation.