| Allelopathy refers to the direct or indirect positive or negative effects exerted on plant itself or other plants,microbes or insects by plant’s release of chemicals to the environment,including intraspecific autotoxicity and interspecific allelopathy.Domestic researchers have proved that the accumulation of allelochemicals is an important reason which declined the soil fertility of Cunninghamia lanceolata plantation.In order to understand the effect of Cunninghamia l.endophyteon on Cunninghamia l.allelopathy and to provide new ideas and methods to ease the Cunninghamia l.autotoxicity,this study chose the annual Cunninghamia l.seedlings as materials,and we used Cunninghamia l.endophytic fungus screened by the Forest Ecology Institute of Fujian Agriculture and Forestry University(the strains had been saved by Microbiology Culture Collection Institute of Chinese Academy of Sciences)to establish different Cunninghamia l.endophytic fungus symbionts.Experiments were conducted to investigate the influences of three Cunninghamia 1.allelochemical stress on some physiological process of Cunninghamia l.and Cunninghamia l.-endophytic fungus symbionts,including chlorophyll content,chlorophyll fluorescence,membrane permeability and protective enzyme activities,biomass and seedling height.The main results are as follows:1.Effects of endophytic fungus on the chlorophyll content of Cunninghamia l.seedlings under allelochemical stressUnder the allelochemicals L and LR stress,endophytic fungus did not improve the content of chlorophyll-a,chlorophyll-b and chlorophyll-a+b of Cunninghamia l.seedlings.Under the allelochemical H stress,endophytic fungus certainly decreased the allelochemical impact on Cunninghamia l.seedlings,which showed that strain CG2 promoted the rise of chlorophyll-a,chlorophyll-b and chlorophyll-a+b content in the late stage(60 d)significantly(P<0.05),but there were not significant differences between the rest endophyte-infected Cunninghamia l.seedlings and endophyte-free Cunninghamia l.seedlings(P>0.05).2.Effects of endophytic fungus on the chlorophyll fluorescence parameters of Cunninghamia l.seedlings under allelochemical stressUnder the three allelochemicals stress,endophytic fungus had no significant promoting effect on the Fv and Fm of leaves in Cunninghamia l.seedlings,but it played a certain role in decreasing Fo,while improving F,/Fm and Fv/Fo of Cunninghamia l.seedlings.Under allelochemical L stress,endophytic fungus decreased the Fo of Cunninghamia l.seedling which mainly occurred in the middle stage(45 d)and late stage(60 d),and the influence of strain aJ4 was the best while the strain Ca was weakest;All of three strains improved the Fv/Fm and Fv/Fo of Cunninghamia l.seedling in the late stage(60 d)with medium(40 mg·L-1)allelochemical L stress,effects of the three strains showed a trend that CG2>aJ4>Ca.Under allelochemical LR stress,reduction effect of strain CG2 and aJ4 on Fo of Cunninghamia l.seedlings occurred in the middle stage(45 d)with medium(40 mg·L-1)and severe(120 mg·L-1)allelochemical LR stress as well as every allelochemical LR stress in the late stage(60 d),and the effect of former was better than the latter while strain Ca only had effects in the late stage(60 d)in this allelochemical stress;Endophytic fungus had certain effects on promoting the Fv/Fm and Fv/Fo of Cunninghamia l.seedlings in every stage,and the effect of strain aJ4 was stronger than strain CG2 in middle stage(45 d)while it was weaker in the late stage(60 d),and the effect of strain Ca were the worst in every stage.Under allelochemical H stress,strain CG2 and aJ4 significantly decreased Foof Cunninghamia l.seedlings with medium(80 mg·L-1)and severe(120 mg·L-1)allelochemical stress in every stage(P<0.05),while strain Ca was only in early(30 d)and late(60 d)stage;The promoting effect of endophytic fungus on Fv/Fm and Fv/Fo of Cunninghamia l.seedlings was relatively weak under this allelochemical stress,strain CG2 and aJ4 were mainly played a role in early stage(30 d)with slight(40 mg·L-1)and medium(80 mg·L-1)allelochemical stress,and strain Ca did not play a role.So we drew a conclusion that endophytic fungus certainly improved the photosynthesis of Cunninghamia l.seedlings and strain CG2 was best under three allelochemicals stress.3.Effects of endophytic fungus on the membrane permeability and protective enzyme activities of Cunninghamia l.seedlings under allelochemical stress(1)Leaf relative conductivity:Under the three allelochemicals stress,endophytic fungus had similar protection on cell membrane of Cunninghamia l.seedlings,which showed that strains CG2 and aJ4 decreased injury of allelopathy on cell membrane of Cunninghamia l.seedlingsin the middle(45 d)and late(60 d)stage with every allelochemicals stress,and strain CG2 was more effectively to inhibit the rise of leaf relative conductivity than strain aJ4.Strain Ca had certain protective effects on membrane systemof Cunninghamia l.seedling mainly in the middle stage(45 d)with slight(40 mg·L-1)and severe(120 mg·L-1)allelochemical stress.(2)Soluble protein content:Compared with the endophyte-freeCunninghamia l.seedlings,the endophyte-infected Cunninghamia l.seedlings could withstand higher allelochemicals stress,and was more sensitive to allelochemicals stress;Comprehensive analysis of the soluble protein content of endophyte-free and endophyte-infected Cunninghamia l.seedlings,we can know that endophytic fungus effectively avoided the normal protein synthesis of Cunninghamia l.seedlings to be blocked,then improved its ability to fight the allelochemicals stress,which showed that strain CG2 effectively promoted the rise of soluble protein content of Cunninghamia l.seedlings in middle(45 d)and late(60 d)stages with every allelochemicals stress,the strain aJ4 relieved the damage of allelochemicals stress on Cunninghamia l.seedlings mainly in late stage(60 d)with slight(40 mg·L-1)and medium(80 mg·L-1)allelochemicals stress,and strain Ca had certain protective effect on Cunninghamia l.seedlings under allelochemical L and LR stress.(3)The content of MDA:Under three allelochemicals stress,the content of MDA of endophyte-free and endophyte-infected Cunninghamia l.seedlings increased with stress rising,but endophytic fungus alleviated the injury of allelochemicals stress on cell membrane of Cunninghamia l.seedlings in early stage(30 d),and effects of the three strains showed a trend that CG2>aJ4>Ca.From comprehensive analysis of the change of MDA content in three endophyte-infected Cunninghamia l.seedlings,we knew the content of MDA could maintain a relatively stable level at a higher allelochemicals stress and a longer period by strain CG2 effect(4)The activity of SOD:Under allelochemical L stress,strain CG2 significantly improved the activity of SOD of Cunninghamia l.seedlings in every stage(P<0.05),and the effect was the most significant in the late stage(60 d),and strain aJ4 promoted the oxygen scavenging capacityof Cunninghamia l.seedlings mainly in the middle(45 d)and late(60 d)stage,and slight(40 mg·L-1)and severe(120 mg·L-1)stress were better,but strain Ca had a certain effect only in the late stage(60 d)with slight(40 mg·L-1)and severe(120 mg·L-1)allelochemical L stress.Under allelochemical LR stress,strain CG2 effectively relieved the allelochemical impact on cell membranes of Cunninghamia l.seedlings in every satge with every allelochemical LR stress while that of strains Ca and aJ4 were in the late stage(60 d),and the effect of former was stronger than the latter.Under allelochemical H stress,strain CG2 and aJ4 significantly enhanced the activity of SODof Cunninghamia l.seedlings in different stage with every allelochemical H stress(P<0.05),but that of strain Ca only in late stage(60 d)and the other stages was not significant(P>0.05).From the comprehensive analysis,we got the conclusion that endophytic fungus played a certain role in promoting the activity ofSODof Cunninghamia l.seedlings under three allelochemicals stress,and the effect of three endophytic fungus showed a trend:CG2>aJ4>Ca.(5)The activity of POD:Under allelochemical L stress,strain CG2 significantly enhanced the activity of POD of Cunninghamia l.seedlings in different stage with every allelochemical L stress(P<0.05),and that of strain aJ4 was mainly in middle(45 d)and late(60 d)stage with medium(80 mg·L-1)and severe(120 mg·L-1)stress while strain Ca only enhanced the activity of POD of Cunninghamia l.seedlings in the late stage(60 d)with severe(120 mg·L-1)stress.Under allelochemical LR stress,strains aJ4 and Ca eased allelopathic impact on the cell membrane structure of Cunninghamia l.seedlings mainly in every stage with medium allelochemical LR stress(40 mg·L-1),and that of strain CG2 was in every stage with every stress,and the effect was more significant in late stage(60 d).Under the allelochemical H stress,strain CG2 had a significant protective effect on Cunninghamia l.seedlings in early stage(30 d)with every stress(P<0.05),and that of strain aJ4 was only in same period with slight(40 mg·L-1)stress while strain Ca did not increased the activity of POD of Cunninghamia l.seedlings during this period,but in the middle(45 d)and late stage(60 d)with every stress,three endophytic fungus had effective effect on relieving impact on the cell membrane of Cunninghamia l.seedlings,and the effect showed a trend that CG2>aJ4>Ca.In conclusion,endophytic fungius can enhance the activity of POD of Cunninghamia l.seedlings and enhance its resistant ability to the autotoxicity,but there were certain differences between different endophytic fungi.4.Effects of endophytic fungus on the height,ground diameter and biomass of Cunninghamia l.seedlings under allelochemical stressUnder three allelochemicals stress,endophytic fungus played a certain role in promoting the growth of Cunninghamia l.seedlings,and accelerating the accumulation of biomass.Among them,the effect of strain CG2 was best,while the effect of strain Ca was weakest. |
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