Effects of different calcium supply levels on growth, mineral element absorption and related physiological and biochemical characteristics of Rosa roxburghii seedlings

Abstract:【Objective】Rosa roxburghii Tratt. is widely cultivated in Karst areas of Guizhou, where calcium contents in soil are very high and varied. So far, the calcium requirement characteristics, adaptability to low or high calcium levels, and the effects of calcium deficiency or excessive calcium supply on growth, mineral element absorption and related physiology of R. roxburghii have been unclear. To explore the effects of different calcium levels on the growth, mineral element absorption and related physiological and biochemical characteristics of R. roxburghii seedlings, the experiment was undertaken, which was beneficial to not only understanding the calcium requirement characteristics, but also revealing adaptability and physiological and biochemical mechanism of R. roxburghii seedlings in calcium-deficient or calcium-excessive environments. Furthermore, this research can provide physiological basis for nutrient management and help to develop regulation practices for the cultivation of R. roxburghii in Karst areas.【Methods】In this research, the seedlings of R. roxburghii Tratt. Guinong 5 were treated with different calcium supply levels by substrate situation method. Six different calcium supply levels (0, 50, 100, 150, 200 and 250 mg · L^-1 ) were applied in this experiment. The growth indexes, the root morphological indexes and root activity, the content of mineral elements in whole plants, the activities of NR, GS, APase, SOD, CAT, POD and the content of MDA in leaves and roots were determined. The correlation between different calcium supply levels and the above indexes were analyzed, and the subordinate function values of the above indexes were calculated.【Results】The results showed that the R. roxburghii seedlings treated with 50 mg ·L^-1 calcium supply level performed the best as compared with other treatments, with the biggest plant height and base diameter, the greatest biomass of whole plant, shoot and root, and the largest total root length, total root surface area, total root volume, root average diameter and total root tip number. The concentrations of N, P, K, Fe, Cu, Zn and B of seedlings treated with 50 mg·L^-1 calcium supply level were the highest, and the contents of Mg and Mn of seedlings treated with 100 mg·L-1 calcium supply level were the largest. The activities of NR, GS, SOD, CAT, POD in leaves and roots of seedlings all were inhibited when the supplying level of calcium was lower or more than 50 mg ·L^{- 1} , but the APase activity, MDA content and root/shoot ratio increased. Different calcium supply levels showed quadratic nonlinear regression relationship, significant or extremely significant higher than the indexes. There was an extremely significant and positive correlation between the Ca content in R. roxburghii seedlings and calcium supply levels. In addition, the plant height, the base diameter, the biomass and the root morphology indexes in R. roxburghii seedlings under these treatments with calcium supply levels higher than 100 mg·L^-1 were all lower than those under the treatment without supply calcium. The subordinate function comprehensive analysis showed that at the 50 mg · L^{- 1} calcium supply level, the subordinate function values and comprehensive ranking of the growth indexes, the root morphology, the mineral element content, the nutrient absorption related physiological and biochemical indexes and the physiological and biochemical indexes related to stress resistance of R. roxburghii seedlings were the biggest.【Conclusion】R. roxburghii had the characteristics of excessive absorption to calcium, but the quantity demand of calcium was not high. Under this experiment conditions, the calcium supply level of 50 mg ·L^{- 1} was the most beneficial to the growth and mineral element absorption by R. roxburghii seedlings. The growth was inhibited significantly when these calcium supply levels were more than 100 mg·L^-1 . The mineral element absorption except Ca2+ of R. roxburghii seedlings was inhibited after it absorbed too much Ca2+ . R. roxburghii seedlings had an adaptability to low calcium stress or high calcium stress, but this adaptability was not very strong. The tolerance of R. roxburghii seedlings to high calcium stress could be realized by the change of biomass allocation. The decrease of shoot growth and the increase of root/shoot ratio were important strategies for R. roxburghii to adapt high calcium stress. In conclusion, the results of this study could provide a scientific basis for nutrient management and regulation of R. roxburghii cultivation on high calcium soil in Karst area.