Morphology And Physiological Response Of Invasive Plant Xanthium Italicum To Drought Stress

In this study,an invasive plant,Xanthium italicum,was used as a test material,using PEG-6000 simulated drought method to study the germination characteristics,seedling growth and physiological response of Xanthium italicum seeds to drought stress(5%,10%,15%,20%,25%);Then,using potted water-control,set four moisture gradients,the normal water supply(85%-80% of water holding capacity in field),mild drought(70%-65%),moderate drought(50%-55%)and severe drought(40%-35%)were measured for physiological index,photosynthetic index,chlorophyll fluorescence index and growth index in different growth periods,to study the morphological and physiological responses of the drought in Xanthium italicum,the aim is to provide scientific basis for the study of invasive plant invasion mechanism.The main results of the study are as follows:1.The seed germination of Xanthium italicum was related to the degree of stress response to PEG stress.With the increasing concentration of PEG stress,the germination and seedling growth of Xanthium italicum seeds were inhibited significantly,and the hypocotyl was the most sensitive to PEG stress.Resurgence test showed that Xanthium italicum seeds have strong resistance to PEG stress.When the seed of Xanthium italicum was under PEG stress,the cotyledons,hypocotyl and primary roots all start osmotic regulators to maintain osmotic pressure in the membrane system,but the activation of antioxidant enzymes is not the same,which also leads to the different injury degree.2.The physiological response of Xanthium italicum to drought stress is related to the degree of drought stress and the duration of drought stress.In different growth periods,with the increase of drought stress,the damage degree of Xanthium italicum membrane system is different,among which the content of MDA in the nutrient period is significantly higher than CK,while the MDA content of severe drought is relatively lower,Xanthium italicum mainly through the accumulation of a large number of soluble protein and free proline to regulate cell osmotic pressure,to resist drought;But the activation mechanism of antioxidant enzymes is different.With the increase of the growth periods,the damage degree of membrane system was different under different drought stress,and the reproductive period was the most serious.Xanthium italicum mainly maintains high free proline content and POD activity to maintain the membrane system osmotic pressure balance and decomposition of toxic substances,to resist damage,and increase with the drought stress,the stronger resistance.3.In different growth periods,the photosynthetic response of Xanthium italicum to drought stress is different.During the nutrition period,there was no significant change in chlorophyll content,photosynthetic index,Fo?Fm?Fv/Fm?Fv and Fv/Fo under various treatments,and Yiled?ETR and qP were significantly higher than CK under moderate and severe treatment,indicating that the chloroplast structure of Xanthium italicum was not destroyed under drought stress during the nutrient period,and the electron transfer was enhanced.Able to maintain a certain photosynthetic ability,breeding period,with the increase of drought stress,the Chla content,Chlb content,Chl(a+b)content,Pn?WUE and Ls of Xanthium italicum all showed a gradual upward trend,under severe drought Chla content,Chlb content,Pn ? WUE and Ls were significantly higher than CK,There was no significant change in Chla/Chlb and fluorescence index,which indicated that the chlorophyll structure of Xanthium italicum was not destroyed under drought stress during breeding period,and its content increased,which led to the gradual enhancement of photosynthetic ability,which showed that of Xanthium italicum had certain resistance to drought stress.With the prolongation of the growing period,there was no significant change in chlorophyll content,Fo?Fm and Fv of Xanthium italicum under various droughts,the Pn was significantly higher than that of nutrition during severe treatment,and Yiled?ETR and qN significantly decreased,indicating that Xanthium italicum had certain self-protection ability and could maintain high photosynthetic ability under severe drought to resist drought stress.4.During the breeding period,Xanthium italicum has certain morphological plasticity and biomass distribution strategies in the level of nutritional components to drought stress.With the aggravation of drought stress,the number of stem,leaf and root components of Xanthium italicum was significantly decreased,inhibiting the growth of Xanthium italicum,and the most significant inhibition under severe drought.However,the distribution of biomass,SLA and the root/shoot ratio did not change significantly,and no death and yellowing of leaves were found in Xanthium italicum under severetreatment,indicating that under drought stress,Xanthium italicum can develop normally,and has certain ability to resist drought.To sum up,the seed germination of Xanthium italicum is sensitive to PEG stress,seedling growth is limited,but in the growth process,Xanthium italicum mainly through the initiation of osmotic regulation of substances and antioxidant enzyme activity and enhance photosynthetic capacity,to resist the impact of drought stress on it,it can also be well adapted to growth and diffusion in arid areas.