| Magnesium is an important and essential nutrient for plants, and plays an important role in plant growth, photosynthesis, active oxygen metabolism and overall physiological metabolic activity. Dehong district has a subtropical monsoon climate type and is one of the few optimum lemon growing regions in China. Preliminary investigations found that Trifoliate/Eureka easily develops Zn deficiency symptoms, while Trifoliate/Yunning No.1 is prone to develop symptoms of Mg deficiency. A pot sand culture experiment was conducted with different levels of Mg2+(0, 6, 12, 24, 48, 96 mg/L). Plant leaf chlorophyll concentrations, increases of height and number of branches, antioxidant enzymes and nitrate reductase activities were all measured to evaluate the responses of 12 different scion/rootstock combinations of lemon seedlings to different Mg levels. The objective of the study was to select scion/rootstock combinations that are resistant to magnesium deficiency and can improve fruit yield and quality and promote sustainable development of the industry. The main results are as follows:1. Significant differences occurred in plant height, numbers of branches, leaf chlorophlll concentrations and nitrate reductase activities between the 12 different scion/rootstock combinations grown under different Mg levels. Evaluated on the basis of increases in relative plant height, the scion/rootstock combinations seriously restricted by Mg deficiency were Y/R3 and S1/Z, these restricted significantly were Y/R2, Y/R6, Y/R7, S2/Z and S3/Z, while Y/R1, Y/R4, Y/R5, S4/Z and S5/Z were not affected by Mg deficiency. Evaluated on the basis of relative plant branching, the scion/rootstock combinations seriously trstricted by Mg deficiency were Y/R4, S1/Z and S4/Z, significantly restricted were Y/R2, Y/R3, Y/R6, Y/R7 and S3/Z, while Y/R1, Y/R5, S2/Z and S5/Z were not affected by Mg deficiency. Evaluated on the basis of relative leaf chlorophyll concentrations, the scion/rootstock combinations seriously restricted by Mg deficiency were Y/R3 and S1/Z, significantly restricted were Y/R2, Y/R4, Y/R6, Y/R7, S4/Z and S5/Z, while Y/R1, Y/R5, S2/Z and S3/Z were not affected by Mg deficiency. In Y/R1, Y/R3, S2/Z and S4/Z, Mg-deficient leaves had higher or similar activities of NR than other Mg levels treatment. The NR activity of other scion/rootstock combinations reached maxima at different levels of Mg treatment. We can use leaf chlorophyll concentrations to evaluate the responses of young lemon seedlings with different scion/rootstock combinations to different magnesium levels, in the selected scion/rootstock combinations, Y/R3 and S1/Z were seriously restricted by Mg deficiency and Y/R1, Y/R5, S2/Z were not affected by Mg deficiency.2. Of the selected scion/rootstock combinations, Y/R3 and S1/Z were seriously restricted by Mg deficiency and Y/R1, Y/R5, S2/Z were not affected by Mg deficiency. The effects of different Mg levels on nutrient concentrations in different organs from these 5 different scion/rootstock combinations are as follows: the Mg, Ca, Fe, Mn, Cu and Zn concentrations in different plant organs from Y/R3 and S1/Z were higher than for in Y/R1, Y/R5 and S2/Z.3. Significant differences were observed on antioxidant enzyme activities and MDA content of the 12 different scion/rootstock combinations under different Mg levels. In Y/R1, Y/R5, S2/Z and S3/Z, Mg-deficient leaves have higher or similar activities of SOD, POD, CAT than at other Mg levels. Mg-deficiency reduces leaf MDA content. However, in contrast, Y/R3 and S1/Z have lower levels of SOD, POD, CAT under conditions of Mg deficiency.These results show that Y/R3 and S1/Z are seriously restricted by Mg deficiency and Y/R1, Y/R5, S2/Z are not affected by Mg deficiency. The Mg, Ca, Fe, Mn, Cu, Zn concentrations in different organs of Y/R3 and S1/Z are higher than for Y/R1, Y/R5 and S2/Z, the nutrients required for growth are more than others, which are easy to occur nutrient deficiency symptoms. |
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