The Drought Adaptation Strategies Of Invasive Plant Cenchrus Pauciflorus

The impact of global change and human activities on climate is mainly reflected in the change of precipitation pattern and the emergence of extreme climate.In recent years,the frequency and area of drought events have been increasing,the degree of invasion caused by invasive plants has become more serious,and the negative impact on the ecological environment and human society has become more serious.To study the physiological adaptation mechanism of invasive plant Cenchrus pauciflorus Benth.(C.pauciflorus)under drought conditions,analyze the drought resistance of C.pauciflorus under different drought conditions,and provide a theoretical basis for the prevention and control of C.pauciflorus.In this study,C.pauciflorus was used as the experimental material,and the following treatments were set:(1)Gradual drought stress experiment with two water gradients of sufficient water supply and stop water supply.(2)Long-term drought stress experiments of 80%,55% and 35% FWC three water gradients.(3)The post-drought rewatering experiment of five water gradients of 80%,55%,35%,55%→80%,35%→80%FWC.(4)Field sampling experiments in arid habitats.The effects of different drought degrees on the morphological and physiological indexes of C.pauciflorus are studied,and the adaptation strategies of C.pauciflorus to drought are discussed.The main results are as follows :Gradual drought experiment showed that with the continuous extension of stress time,Gs and LRWC decreased,while MDA content,Pro content,SS content,SOD activity,POD activity all significantly increased.CAT activity gradually increased first and then decreased,with values smaller than the control group.Long-term drought stress experiment showed that with the increase of stress degree,plant height and tiller number decreased gradually,ear position coefficient had no significant difference,fruit weight per plant increased first and then decreased.MDA content,SOD and POD activities gradually increased,and CAT activity was the highest under moderate stress.There were significant differences in the biomass of above-ground organs among different treatments.The stem biomass,leaf biomass and total above-ground biomass decreased significantly,and the fruit biomass was the highest under moderate drought stress.The distribution ratio of biomass among different aboveground organs was different.The effect of severe drought on the late growth stage was more significant.The decrease of soil water content significantly shortened the fruiting time and accelerated the growth progress.The rehydration experiment after drought showed that the root dry weight increased significantly after rehydration,and the rehydration had little effect on the main root length.Rehydration had no significant effect on the biomass of aboveground organs,but there were significant differences among the control group,stress group and rewatering group.Severe drought had a greater impact on chlorophyll content.After rehydration,chlorophyll content and leaf thickness increased,but still lower than the control group,showing a compensatory effect.Rehydration after moderate drought had a significant effect on plant height,tiller number had a more significant response to rehydration after severe drought stress,and leaf thickness had no significant change.Rehydration after drought can alleviate the effects of drought stress.The results of field investigation showed that there were significant differences in the total biomass of C.pauciflorus in different habitats: grassland>semi-humid sandy land>grazing land>bench land,and there was a significant correlation between the biomass of each organ and the total biomass.The leaf biomass allocation ratio was the largest in the bench land.There were significant differences in phenotypic plasticity indexes(PI、CV)among different habitats,with the largest in semi-humid sandy land and the smallest in grassland.The maximum R/S was 0.1019 in bench land,and 0.0983,0.0479 and 0.0408 in grazing land,semi-humid sandy land and grassland,respectively.There was a significant correlation between the biomass of each organ.The correlation coefficient between leaf biomass and total biomass was 0.984,and the correlation coefficient between RB-FB was0.528.The allometric growth index of RB-TB and FB-TB in grassland,semi-humid sandy land and grazing land habitats was not significantly different from 1,showing an isometric growth,and an allometric growth relationship of less than 1 in bench land habitats,indicating that the distribution ratio of small individuals to reproduction and root biomass in C.pauciflorus population was greater than that of large individuals,and the transformation of small individual trophic body to propagule increased to ensure that it could still have reproductive output when encountering severe drought stress.Compared with the ALB and AFB,ARB and ASB was more affected by the degree of habitat invasion.In summary,the drought-tolerant adaptation strategy of C.pauciflorus under moderate drought stress reduces the biomass allocation of nutrients,increases the biomass allocation of propagules and prolongs the growth and development time,thereby obtaining greater seed yield,which is conducive to the expansion of soil seed bank.Under severe drought stress,the adaptation strategy of escaping from drought further reduced the biomass allocation of vegetative organs,increased the conversion rate to propagules,completed the life cycle quickly in a short period of time,and obtained a greater reproductive success rate,which is conducive to its adaptation to extreme climate.Therefore,C.pauciflorus can change the drought adaptation strategy under certain conditions,complete the life history,and achieve the purpose of invasion.In the meadow habitat with relatively good water conditions and stable environment,the biomass is the largest and the variation is the smallest,which can produce more propagules and contribute to the expansion of the population.In the bench land with large changes in water conditions,the reproductive allometric growth index is less than 1.When suffering from severe drought stress,the transformation from vegetative body to propagule increases to ensure the reproduction of the population,which is more conducive to its adaptation to the changing climate conditions and its rapid spread in Horqin Sandy Land.