Abstract:

This research investigated the adaptation mechanism of Pueraria lobata to the calcium-rich karst environment. P. lobata germplasm lines were sourced from Australia （AUS）， Jiangsu （JS） and Hunan （HN）. To investigate the effects of excess calcium （Ca） stress on seed germination， seedling growth， osmoregulatory substances， antioxidant enzyme systems and endogenous plant hormones， seeds of the three P. lobata germplasm lines were germinated at different concentrations （0， 50， 100， 150 and 200 mmol·L^-1） of CaCl₂. It was found that seed germination rate， germination potential， germination index and vigor index of the AUS and JS germplasm lines were significantly reduced and seed germination rate， germination speed and seedling vigor were significantly inhibited with increasing calcium salt concentration （P<0.05）， while seed germination rate， germination potential and germination index of Hunan germplasm were increased at 100 mmol·L^-1 CaCl₂ compared to other concentrations. With increasing CaCl₂ concentration： i） The leaf length， leaf width， plant height and biomass of seedlings of the three P. lobata germplasm lines were significantly reduced； ii） Malondialdehyde （MDA） and relative conductivity of seedlings of the three P. lobata germplasm were significantly increased； iii） Proline （Pro）， soluble sugar content and superoxide dismutase （SOD） and catalase （CAT） activities of leaves were initially increased and then decreased； iv） The leaf peroxidase （POD） activity increased and then decreased in AUS and HN germplasm， while in JS germplasm POD activity showed a significant increase； v） The ascorbate peroxidase （APX） activity increased significantly in HN and JS germplasm， while AUS germplasm showed an initial increase and then decreased； vi） The leaf ABA， IAA and GA₃ contents initially increased and then decreased in all three P. lobata germplasm lines， while zeatin did so for AUS and HN， but not JS germplasm. The seed germination and seedling growth of the three P. lobata germplasm lines were not significantly inhibited by 0-50 mmol·L^-1 CaCl₂ stress， but were significantly inhibited by 150-200 mmol·L^-1 CaCl₂ stress， while seeds of HN germplasm relied on seed dormancy to resist CaCl₂ stress. Hence it was concluded that P. lobata seedlings are tolerant to low CaCl₂ stress. When stressed with medium to high calcium salt concentration， seedlings of P. lobata actively regulated their physiological metabolism by increasing their own osmotic substance content， enhancing antioxidant enzyme activity， increasing some hormones， and changing the biomass of aboveground and underground parts to adapt to high calcium salt environments. Using affiliation function and principal component analysis， all the indicators， except for Pro content and APX activity， were considered to evaluate the salt tolerance of the three P. lobata germplasm lines， and the salt tolerance ranking of the three germplasm lines was JS>HN>AUS.

Key words: Pueraria lobata, calcium salt stress, seedling growth, antioxidant