Effects Of Drought Stress On The Growth And Diosgenin Content Of Rhizome For Dioscorea Nipponica Makino Grown In The Field

In the context of global climate change,the climate of North China continues to show a warming and drying trend,which has severely affected the growth of ecosystems and vegetation.Dioscorea nipponica Makino is a perennial herbaceous vine.Its rhizomes are rich in diosgenin,which is an important medicinal plant for the production of steroid hormones in the north.In this study,two provenances of D.nipponica Makino(Manghe and Pangquangou in Shanxi Province)were used as experimental materials.Soil water content is controlled at 70% to 80%(normal),50%to 60%(light stress),35% to 50%(moderate stress),and 20% to 35%(severe stress)of the maximum water holding capacity in the field,respectively.The influences of drought stress on the plant growth and the rhizome diosgenin content of D.nipponica Makino were studied.Germplasm comparison was also performed based on the consideration of the plant’s drought resistance and medicinal ingredients.The main conclusions were as follows:1.The influence of soil water deficit on the plant morphology of D.nipponica Makino from Manghe was greater than that from Pangquangou.Under drought conditions,the leaf length,leaf width and leaf area of Manghe provenance showed a downward trend during the fruit ripening period of the first year.During the period of vegetative growth,flowering and fruit ripening period of the second year,the leaf aspect ratio and leaf basal angle of Manghe provenance were mostly higher than control,in other words,leaves tended to be of the broad type when the plant was suffered from water shortage.With the intensity of drought stress,the dry weight of aboveground stem of two provenances was both lasting increased during the fruit ripening period of the first year.Under severe stress,the dry weight of Manghe and Pangquangou was increased by 89.51%and 65.71%,respectively.The rhizome volume was decreased by drought.The volume of Manghe provenance under severe stress and the Pangquangou provenance under moderate stress was declined by 36.37% and 39.26%,respectively.2.When the soil was short of water,the superoxide dismutase(SOD)activity of leaves was mostly increased.Under moderate stress,the SOD activity of Manghe provenance was 88.46%higher than control during the fruit ripening period of the first year;that of Pangquangou provenance is 77.83% higher during the flowering period of the second year.During the fruit ripening period of the first year and the flowering period of the second year,the malonaldehyde(MDA)content of leaves of two provenances was both significantly improved by drought.At the fruit ripening period of the first year,the MDA content of aboveground stem of Manghe provenance was prone to be increased with the increasing of stress,and reached a maximum of14.33 μmol·g-1FW under severe stress,an increase of 59.93% compared to control.However,the MDA content of aboveground stem was both decreased by drought stress during the fruit ripening period of the second year.3.At the fruit ripening period of the first year,the proline content of the leaves of Manghe provenance under moderate stress was 2.25 times that of the control group,and that of Pangquangou provenance was increased by 35.77% under severe stress.The proline content of aboveground stem continued to be decreased as the increasing of stress.Under severe stress,that of Manghe and Pangquangou provenance was 79.58% and 76.81% lower than control,respectively.Under drought conditions,the proline content of rhizomes of Manghe provenance was significantly higher than that of the control group.The proline content of rhizomes was also increased by drought,and increased to 48.68 μg · m L-1 under severe stress,an increase of 80.70%compared with the control group.The soluble protein content of rhizomes was both significantly increased by drought: that of Manghe provenance was 89.42% higher than control under moderate stress,and that of Pangquangou provenance was 122.40% higher under light stress.The non-structure carbohydrate content of rhizomes of two provenances was both decreased by drought: under severe stress,that of Manghe and Pangquangou provenance was decreased by46.28% and 20.08%,respectively.4.The content of rhizome diosgenin was moderatly improved by drought treatment: Under moderate stress,the unit content and total mass of rhizome diosgenin of Manghe provenance were improved by 62.85% and 50.00%,respectively.Under light stress,the unit content of Pangquangou provenance was 2.05 times that of the control,and the total mass was 27.30% higher.When the drought stress increased,the content of rhizome diosgenin was significantly decreased:Under severe stress,the unit content and total mass of rhizome diosgenin of Manghe provenance was dropped by 77.78% and 84.79%,respectively,that of Pangquangou provenance was decreased by 82.88% and 88.94%,respectively.5.According to the contribution of each factor to the characterization of drought resistance of D.nipponica Makino,a total of 12 factors including leaves,aboveground stems and rhizomes were selected by the principal component analysis.Then the drought resistance membership function value of two provenances was calculated.The drought resistance function values of Manghe provenance of the first and second year was 0.55 and 0.66,respectively.That of Pangquangou provenance was 0.43 and 0.60,respectively.Drought resistance of Mangahe provenance was significantly stronger than that of Pangquangou.Meanwhile,the quality of medicinal materials of Manghe provenance was better than that of Pangquangou under drought conditions.Under the current arid climate conditions in Shanxi Province,Manghe Provenance was more suitable to be planted in Shanxi Province.