Picea purpurea has a physiological advantage over its progenitors in alpine ecosystems due to transgressive segregation

Picea purpurea originated from the homoploid hybrid speciation, which occupy novel alpine habitats in the north-east region of the Qinghai-Tibet Plateau (QTP) where its progenitors, P. wilsonii and P. likiangensis are excluded. Alpine habitats are usually characterized by low atmospheric CO₂ concentrations and strong solar radiation with a large fraction of shortwave radiation (i.e. blue light). To test whether P. purpurea has the transgressive segregation in photosynthetic capacity and stomatal characteristics contributed to occupying such extreme habitats, we investigated the leaf gas exchange properties at two level of CO₂ concentration (C_a: 200 and 400 μmol mol⁻¹), light responsive curves of photosynthesis under three light qualities (red, blue and a mixture of both red and blue light at the ratio of 94:6), stomatal and other relative physiological traits for all three species. Our results show evidence of transgressive segregation in hybrid species; for instance, under blue and red light P. purpurea was demonstrated has the higher quantum yield of CO₂ assimilation (φ) and maximum CO₂ assimilation rate (A_max) than its progenitors. Particularly φ and A_max in P. purpurea were 2-fold higher than these in P. likiangensis. P. purpurea also exhibited higher stomatal conductance at low CO₂ concentrations and instantaneous water use efficiency under all light qualities, have greater leaf pigments content, longer guard cell length and lower linear stomatal density relative to its progenitors. These traits may have enhanced the physiological fitness of P. purpurea and facilitated its colonization to alpine habitats.