| Broussonetia papyrifera is excellent in growth characteristic, comprehensive economic use and particularly strong in adaptability and other characteristics. In this experiment, different concentrations of lead(150 mg kg-1, 450 mg kg-1, 1000 mg kg-1, 1500 mg kg-1) were conducted to examine lead stress of Broussonetia papyrifera. We aimed to examine the lead resistance response mechanism of Broussonetia papyrifera and to provide a theoretical basis and F0 r Gannan rare earth waste of resistant variety breeding. The main conclusions are as F0llows:Treatment of soil by Pb2+ influenced concentrations of Pb2+ in different periods substantially. At the beginning of the trial, Broussonetia papyrifera was sensitive to Pb2+. Chlorophyll content changed significantly with the increase of Pb2+ concentration and the maximum SPAD value was obtained at 150 mg kg-1 treatment, then gradually decreased with Pb2+ concentrations.The photosynthesis change of Broussonetia papyrifera was impacted by Pb2+ concentration and stress time. At the beginning, each treatment showed significant changes. The photosynthetic rate of Broussonetia papyrifera showed the most obvious response to high Pb2+ concentration. CK differed significantly with the other treatments(P<0.05). Pn, Tr, Gs at low concentrations of Pb2+ were higher than CK. At mid stage of stress, the value of Pn with each treatment increased significantly, the highest was 7.69 μmol m-2 s-1. Pn, Tr, Gs increased remarkably at Pb2+ concentration of 450 mg kg-1,1000 mg kg-1. At later stress period, the advantage of low Pb2+ concentration treatment was no longer obvious. There was no significant difference between the middle and high concentrations of Pb2+ treatments with other treatments(P>0.05). The diurnal change rule of Broussonetia papyrifera in different stress period differed significantly. Early stress(in September), Broussonetia papyrifera had single peak curve diurnal variation, peaking at 14:00 pm. Late(mid-October) had bimodal curve peaks appeared at about between 10:00 and 14:00.The results of the analysis of chlorophyll fluorescence in Broussonetia papyrifera under different Pb2+ stress indicated that: consistent with photosynthetic perF0 rmance, at the beginning, the maximum value of F0 was obtained at concentration of 1500 mg kg-1.There was a significant difference in F0, Fv/Fm and Fv/F0 between treatments and CK(P<0.05). There were significant differences in F0, Fv/Fm and Fv/F0 between treatments and CK at concentration of 1000 mg kg-1 as well. It could be concluded that when the concentration of Pb is greater than or equal to 1000 mg kg-1, photochemical reaction center of the leaves of Broussonetia papyrifera was damaged. At mid stage of stress, the amplitude of change decreased compared to the initial period. The ratio of Fv/Fm, Fv/F at the concentration of 1000 mg kg-1 and 1500 mg kg-1 increased rapidly. At the late stage of stress treatments, the value of F0, Fm, Fv/Fm, Fv/F0 was in line with the normal fluorescent power daily variations. Fm and F0 decreased with the change of temperature and climate.Through the study on physiological biochemical characteristics of leaves, the results showed that: the MDA value, proline content, antioxidant enzyme(SOD, POD, CAT) activities of different concentrations of lead were higher than those of CK. MDA membrane system increased first and then decreased and was more rapid when the concentration is 1500 mg kg-1. The high concentration of lead caused cell membrane damage of Broussonetia papyrifera. The content of proline and lead concentration and soluble protein increased gradually with the stress concentration, correlated with the regulation of proline osmotic cell. The activity of antioxidant enzymes(SOD, POD, CAT) increased gradually with the increase of stress concentration, increasing the adaptability to external stress by enhancing the activities of the antioxidant enzyme system.The study of lead stress by mulberry photosynthesis, chlorophyll fluorescence, physiology and biochemistry showed that Broussonetia papyrifera under the stress of low concentration of 150 mg kg-1 Pb2+ can survive. At the early stage of water stress, plant growth was promoted substantially. While the high concentration(450 mg kg-1,1000 mg kg-1,1500 mg kg-1) of Pb2+ stress on mulberry seedlings growth caused some damage, playing an inhibitory effect on growth with the extension of stress time, the difference between treatments and CK was not significant(P<0.05). |
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