Capability and limitation of regeneration of Rosa hugonis and Rosa soulieana in the dry valley of the upper Minjiang River

It is always a problem faced by concerned scientists and ecosystem managers to improve to the vegetation and restore the degraded ecosystem in the dry valley of the upper Minjiang River in China.Investigation of seed bank and seedling establishment is the most important work to understand plant natural regeneration,prompt its use in conservation,restoration and management.In order to address the regeneration capacity and its limitation of two native rose species(Rosa hugonis and Rosa soulieane),the characteristics of seeds,seed banks and seedling banks were investigated along the dry valley of the upper Minjiang River.60 soil samples with 15 cm×15 cm×5 cm respectively for R.hugonis and R.soulieane were collected to determine the seed densities.20 samples with 2 m×2 m under the crown were investigated for seedling densities.Seed dormancy was identified as germination percentage of 16-week stratified achenes in 5℃ refrigerator.Both rose species produced large quantity of seeds with poor quality.Relatively low seed number((627.6±216.3)hips)and viability((32.25±0.67)%),but high seed weight((13.97±0.23)mg)and deep seed dormancy were observed in R.hugonis compared with R.soulieane.Two rose species showed the similar distribution pattern of soil seed bank in both upright and horizontal positions.Seeds mainly distributed in the soil surface,and the higher seed density was often observed near the clump.Both R.hugonis and R.soulieana showed high total seed densities((560±90)and(1955±235)seeds/m2,respectively),but low viable seed densities((26±4)and(152±18)seeds/m2,respectively).Viable seeds of R.hugonis were distributed deeper in soil than those of R.soulieana.However,much more R.hugonis(65.3%)seeds were nibbled compared to R.soulieana(0.5%)seeds.Additionally,the seedling density of R.hugonis((4.28±0.49)individuals/m2)was slightly lower than that of R.soulieana((5.24±1.28)individuals/m2).Most seedlings were only between 1 and 5 cm high for both species.The results suggested that both rose seeds are dormant and have persistent soil seed banks.The distribution and composition of seed banks and seedling banks are closely related to seed characteristics.Poor regeneration capability is found in both rose plants,and R.hugonis behaves better than R.soulieana.The main limitation of regeneration might be the seed destroying by rodents for R.hugonis and the high seedling mortality for R.soulieana.