| Based on the differences of the insect pest resistance among hybrid poplars the research on the resistance of hybrid poplar mixed plantation and the resistant mechanism were carraied out through estimate the impact of the plantation on the arthropods diversity,and reponse of poplars to important defoliator gypsy moth(Lymantria dispar Linneaus)damage under different planting patterns to provide theoretical basis for the prevention and control of pests.Taking four commonly used poplar hybrid or clones in northeast China as plant materials,namely Yingchun No.5(p.smonii × p.nigra),Xiao × Hei(p.smigra × p.smimonii),Xiaohei 14(p.smigra × p.smimonii),and Yinzhong poplar(p.smirba × p.bierolinensis),Five treatments of4 pure plantations and mixed plantation with above 4 ones were constructed and 4 random block were set,which with a total of 2880 poplar samples in 20 plots,covering an area of 2.31 hectares.Continuous field investigation were conducted for 4 years.The third instar larvae of gypsy moth(Lymantria dispar Linneaus)were used to test the induce resistance of the poplars to insect pests.From the perspectives of population ecology,chemical ecology,biochemistry and molecular biology,we used methods of community arthropod diversity analysis,GC-MS,LC-MS,metabolomics,transcriptomics combined with field investigation and laboratory research,the pest resistance performance and pest resistance mechanism of hybrid poplar plantation in different forest modes were comprehensively demonstrated.It provides the theoretical basis and guidance for poplar plantation afforestation and integrated pest management.The main research results are as follows:(1)The differences among the four hybrid poplars were significantly greater than the influence of planting modes.Among the four varieties,Yinzhong poplar was the dominant one,and Yingchun No.5 was the relatively weak one on insect pest resistance.In the mixed forest,the growth characteristics of each tree varieties showed additive effect,and there were the phenomenon of the stronger the stronger and the weaker the weaker through the competition between tree varieties.There were differences in insect pest resistance between the two varieties Xiao × Hei and Xiaohei 14.The leaf damage rate of mixed forest was relatively stable for 3 years,showing the insect resistance of dominant species,which was the result of additive effect.The leaf damage rate of Yingchun No.5 was the highest in mixed forest.The leaf damage rate of all tree species in mixed forest was lower than that of pure forest except Yinzhong poplar,showing the non-additive effect of combined resistance.By strengthening the diversity of poplars and planting higher resistance varieties,the combined resistance can be improved,the incidence of diseases and insect pests can be reduced,and the stand quality can be improved.(2)The arthropod diversities were improved in mixed stands compared to pure stands.The community structure index among 5 stands,the mixed forest had the highest arthropod species diversity index,followed by Yingchun No.5 pure forest,and Yinzhong pure stands had the lowest diversity index.Although the abundance of the pest subcommunity in the susceptible pure forest of Yingchun No.5 was greater than that of the mixed forest,the diversity index was smaller than that of the mixed forest,and the abundance and diversity index of the mixed forest were higher than that of the natural enemy subcommunity of Yingchun No.5.The evenness and diversity index of mixed forest were the highest among the five treatments,which indicated that mixed forest could improve the abundance and diversity of arthropod community,and proved that mixed poplar plantation could improve the stability and ecological function of stand.The mixed planting of tree species diversity can improve the resistance of stands to leaf eating pests.Mixed forest increased the number of natural enemies.Compared with monoculture,the mixed culture of four varieties of poplar increased the diversity of related arthropods,indicating that the planting of poplar diversity has the potential to improve the living environment of a variety of arthropods.(3)After attacked by third instar gypsy moth larvae of the mixed plantation of hybrid poplar trees of different diversity,33 volatiles of Yingchun No.5 were detected in different stands,among which 24 were identified.After fed by gypsy moth larvae relative emission rates of(E)-β-ocimene,δ-cadinene,germacrene and benzyl cyanide significantly increased while which of(E)-β-caryophyllene,(E,E)-α-farnesene and myrcene significantly decreased.Except 4 variarty mixed forest that of(3S)-linalool also significantly decreased.For neighboring plants relative emission rates of germacrene significantly increased compared with control after feeding,which of δ-cadinene in pure forest and 2 variety forest significantly increased higher than that in control,while which of myrcene significantly decreased.As for different forest types relative emission rates of(3S)-linalool,(E)-β-ocimene and δ-Cadinene in mixed forest were significantly higher than that in pure forest while which of myrcene were significantly lower than that in pure forest.For neighboring plants relative emission rates of(E)-β-Caryophyllene and(E,E)-α-farnesene in mixed forest were significantly higher than that in pure forest,while that of δ-Cadinene,(E)-β-ocimene and indole significantly lower than that in pure forest.(4)On the 1-year old cuttings of poplar Yinzhong and Yingchun No.5,after feeding by third instar gypsy moth larvae for 48 h,and the metabolomic analysis of the affected and control strains was conducted by using LC-MS.The metabolites of the two hybrid poplars were significantly different,and the metabolites of the same hybrid under different camp forest models were slightly different.The metabolites of Yingchun No.5 and Yinzhong in mixed forest and Yingchun No.5 in mixed forest were obviously intermingled with each other.The above results showed that the effect of poplar metabolites in mixed forest was weaker than that in pure forest.This is consistent with the previous field pest survey results.The amount of metabolites of the same tree species before and after pest treatment in mixed forest was much lower than that in pure forest.In the pure forest,poplars had stronger insect resistance and produced more metabolites.Flavonoid compounds are important metabolites for insect resistance of poplar,and there are significant metabolic changes in different stands.According to the analysis of metabolic pathway enrichment,the different metabolites of the two poplars are involved in several metabolic pathways related to amino acid synthesis and secondary metabolites synthesis.(5)A high throughput sequencing technique based on Illumina Hiseq X Ten platform was used to compare the transcriptome of 18 poplar samples fed bythird-instar gypsy moth larva in experimental and control groups.According to the enrichment analysis of biological pathways of different genes,there were the changes of adaptation to insect pests in different biological pathways after feeding,in experimental group and the levels of DNA,RNA and proteins had be affected.The responses of hybrid poplar to insect pests were comprehensive.When comparing the insect-resistant aspen Yinzhong and the susceptible Yingchun No.5,it was found that there were significant differences in the genes related to the pathogen interaction pathway,.Meanwhile,plant pathogen interaction pathways,plant hormone signal transduction pathways and MAPK signal transduction pathways were significantly enriched,and these pathways were significantly correlated with plant disease resistance and insect resistance.There were significant differences in resistance of many important defense genes(NPR1、NPR3、NPR5、PSBY、PAD4、TPIN、CP26、XTR8、CYP、RPS2、NIMI)in plants treated with different treatments.For example,the expression of NPR1,4 protein/lipase(PAD4)gene in Yinzhong poplar was significantly up-regulated after feeding in the control,pure forest and mixed forest.Compared with Yingchun No.5,a large number of related genes were up-regulated in the pure forest and mixed forest of Yinzhong poplar,indicating that Yinzhong poplar had better resistance than that of Yingchun No.5,which was consistent with the results of sample plot investigation.In different plantings,both poplars had a large number of up-regulated expression of insect-resistant genes in mixed forest,indicating that hybrid poplar mixed plantation could improve stand resistance. |
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