Divergent gas-exchange and chlorophyll fluorescence in F1 hybrids driving habitat differentiation compared to their parents in Buddleja

Background Inter-specific hybridizations were common and can easily take place in Buddleja , and it was an important way for evolution and rapid speciation. The F1 hybrid in this study was a newly identified inter-specific hybridization between B. crispa and B. offic inalis in Sino-Himalayan region. In the natural hybrid zones, F1 hybrids always occupy different habitats from their parents. The objective of this study was to explore environmental acclimatization of F1 hybrids and their parents at physiological and biochemical levels.Results The results showed that F1 hybrids performed as an intermediate in adaptation to their parents, with divergent gas-exchange and chlorophyll fluorescence features. F1 hybrids showed the parallel light compensation point and light saturation point with their parents, but low utilization efficiency to low-light density. They synthesized the greatest total chlorophyll content (10.41 ± 0.56 mg•g -1 ) in leaves than their parents. During the diurnal variation of photosynthesis, F1 hybrids markedly decreased and preserved the stomatal conductance and leaf transpiration rate at a low level. However, they kept high carbon assimilation rate and water-use efficiency with markedly increased vapor pressure deficit. In F1 hybrids, the maximum net photosynthetic rate, maximum water-use efficiency and maximum vapor pressure deficit were 10.48 ± 0.50 mmol CO 2 •mmol -1 photo, 21.52 ± 2.20 µmol•mmol -1 and 4.18 ± 0.55 kPa, respectively. In addition, all Buddleja species performed well and grow healthy with high level of the maximum photochemical efficiency of PSII and low non-photochemical quenching, 0.83 ± 0.004 - 0.85 ± 0.004, and 1.22 ± 0.15 - 1.97 ± 0.08, respectively. In F1 hybrids, they showed great photochemical activity compared to their parental species with high photochemical quenching. Furthermore, the effective quantum yield and electron transport rate presented a similar behavior.Conclusions The results indicated that F1 hybrids have great photochemical activities and growth acclimatization compared to their parents. Associated with the growth performance of F1 hybrids in the homogenous garden, our results suggested that the divergent gas-exchange and chlorophyll fluorescence patterns may facilitate F1 hybrids to respond to different habitats, and to improve growth performance.