Effects Of Flaveria Bidentis Invasion On Maize Growth And Its Threshold Of Prevention And Control

In this paper,we setted up four kinds of nitrogen gradients and four kinds of mixed planting proportion of maize and Flaveria bidentis to study the effects of nitrogen and different degree of Flaveria bidentis invasiveness on maize growth,photosynthetic and yield indexes changes.By methylation-sensitive amplified polymorphism（MSAP）technology,the epigenetic variation and phenotypic plasticity response of maize under different treatments in large bell-mouth period,changes of DNA methylation of Flaveria bidentis and its phenotypic plasticity response characteristics of biomass,growth,and photosynthetic physiological indexeswere also studied.This work will provide theoretical evidence for the prevention and control of invasive plants in farmland.Main results obtained from the work are as follows:1.Different growth stages of the plant height,stem diameter and LAI of maize changed significantly with the planting density increases of the Flaveria bidentis,which were also influenced by nitrogen gradients.The SPAD values and net photosynthetic rates of maize at different growth stages were also affected by the nitrogen gradients and mixed planting proportion.Effects of the mix planting on yield of maize changed with the increase of nitrogen application.When the maize/Flaveria bidentis mixed planting proportion reached2:1（A2）and the nitrogen application rate reached 175 kg·hm^-2（T1）,the Flaveria bidentis mixed planting would have a significant effect on maize yield.The combined effect of mixed planting and nitrogen levels on maize growth and photosynthetic indexes varied with its development of growth periods.At maturing stage of maize,the effect of mixed planting and nitrogen application on maize yield had notable interaction.2.The methylation MSAP analysis was performed on the leaves of maize under different treatments,754 MSAP bands were amplified by 18 pairs of primers and the percentage of primer polymorphism were 95.23%,96.15%,95.09%and 95.09%.The number of un-methylated bands,hyper-methylated bands and total methylated bands in the ratio of A1mixed with other three kinds of mixed planting proportion were significantly different.There was no significant difference in the number of hemi-methylation and per-methylation bands among four mixed planting proportions.Under different treatments,the highest phenotypic plasticity index of maize yield was 0.6393.The phenotypic plasticity index of leaf area index and net photosynthetic rate were relatively high at each growth stage.The phenotypic plasticity index of the height of plant and SPAD were relatively low at each growth stage.There was a significant negative correlation between the level of full-methylated and total methylated level of maize DNA and the net photosynthetic rate.3.The methylation MSAP analysis was performed on the leaves of Flaveria bidentis under different nitrogen treatments,690 MSAP bands were amplified by 18 pairs of primers and the percentage of primer polymorphism was 86.38%.The difference of the semi-methylation and total methylation level was significant between the T2(275 kg·hm^-2)and T3(375 kg·hm^-2)treatments.The increase of nitrogen application rate significantly increased the biomass and root biomass allocation of Flaveria bidentis,promoted the vegetative and reproductive growth as well as photosynthesis of plants,but decreased the biomass allocation of the support structure.The phenotypic plasticity index of flower buds,leaf area index and root biomass of Flaveria bidentis were the highest,which were 0.8247,0.666 and 0.5311,while the phenotypic plasticity index of biomass allocation and photosynthetic physiological index were much lower which indicated that the Flaveria bidentis adapts itself to nitrogen changes mainly by regulating its own nutrition,reproductive growth and root biomass.There was a significant negative correlation between the levels of semi-methylated,full-methylated,total methylated and the number of buds,root biomass,plant height,leaf area index and root biomass,while a significant positive correlation with the leaf biomass.