Synergistic mechanism between photosynthetic performance and growth of interspecific hybrid scions in Catalpa Scop

Abstract

Abstract Background and objective Grafting is a pivotal technique for clonal propagation in Catalpa , yet the regulatory mechanism by which scion genetic background coordinates photosynthetic productivity and growth remains elusive. Methods Using two-year-old Catalpa ovata seedlings as uniform rootstocks, we systematically evaluated photosynthetic physiology, chlorophyll fluorescence, and growth traits across five mating types (18 hybrid combinations). Results Nested ANOVA revealed scion genetic background as the dominant factor governing phenotypic variation. The C. fargesii × C. bungei (HQ) hybrid exhibited superior performance: seedling height (H) (312.05 cm), net photosynthetic rate ( P n ) (16.96 µmol·m⁻²·s⁻¹), total chlorophyll ( C a་b ) (1.96 mg·g⁻¹), and photosynthetic nitrogen-use efficiency (PNUE) (199.07 µmol·mol⁻¹·s⁻¹) significantly exceeded those of other combinations. Chlorophyll fluorescence transients demonstrated an intact photosystem II (PSII) electron transport chain in HQ, whereas the inbred C. bungei (QQ) displayed a ΔK-band, indicating oxygen-evolving complex impairment. Principal component analysis (PCA) confirmed photosynthetic capacity as the core driver of growth variation. Conclusion The growth advantage of HQ arises from a synergistic mechanism integrating high chlorophyll content, enhanced photosynthetic nitrogen-use efficiency, and an intact PSII system. These findings provide a physiological basis for elite scion selection and photosynthetic efficiency breeding in Catalpa within the specific environmental conditions of the southern Henan Plain tested in this single-season study.