Improving nursery performance of Xanthoceras sorbifolium through seed size grading, cotyledon protection, and fertilization management

Background and aims Xanthoceras sorbifolium Bunge, an important woody oilseed species with high ecological and economic value, has seedling quality strongly affected by seed size and nutrient management. In natural habitats, cotyledons are often damaged during germination, potentially compromising early seedling establishment. However, little is known about whether fertilization can compensate for disadvantages caused by small seeds or cotyledon loss. Methods Three factorial experiments clarified how seed traits and nutrient supply shape seedling performance: we examined seed size and cotyledon damage timing on nutrient mobilization, seed size effects on growth under different fertility, and cotyledon removal timing with soil fertility on establishment. Kernel biomass, nutrient (N, P, K, NSC) dynamics, seedling growth, morphology and nutrient accumulation were measured; data analyzed via two-factor ANOVA and t-tests. Results Large seeds had greater nutrient reserves, faster and longer-lasting translocation, and supported rapid early growth. High fertility significantly increased seedling height, diameter, biomass and nutrients, partially offsetting small seed disadvantages. Cotyledon integrity was critical for growth and nutrient accumulation, with early removal suppressing growth—effects not fully alleviated by fertilization. Conclusions Seed size fundamentally determines seedling quality; large seeds benefit from ample reserves and efficient translocation. Maintaining cotyledon integrity is essential, as early loss cannot be fully compensated by fertilization. High fertility improves seedling performance but only partially offsets small seed drawbacks, providing practical guidance for X. sorbifolium nursery practices.