The Growth Response Of Landscape Plants With Different Root Configuration Combinations Under Waterlogging Stress

In recent years,the urban flood disaster has been increasing more and more frequently,and gradually become one of the most important factors affecting the growth of urban landscape plants.However,the response of landscape plants to waterlogging stress is quite different.Some plants can not only adapt to the waterlogged environment,but also do good to alleviate the urban flooding problem.Therefore,how to grow urban plants well-adapted to the future urban flood disaster reasonably and ecologically is an important problem to be solved urgently.The previous method of selecting waterlogging-tolerant plant species one by one may not be able to satisfy the request of landscape diversity and ecology,so it is urgent to explore a new method to afforest urban plant community from a new perspective to meet the increasing urban greening activities demands in the future.In this paper,based on the plant population ecology point of view,to explore the different root configuration combinations of plant response to flooding stress,and from three aspects of morphology,growth and physiological to compare the plants,as well as to study the interaction mechanism between different plants under waterlogging stress,so as to provide a theoretical basis and practice method for afforesting the waterlogging-tolerant urban plant communities in the future.Ilex rotunda and three other life-form plants i.e.herb,shrub and tree--Ruellia simplex,Murraya exotica and Heteropanax fragrans were used as experimental materials to combine with I.rotunda.In other words,four types of different root configuration combinations were composed of I.rotunda-R.simplex(I-R),I.rotunda-M.exotica(I-M),I.rotunda-H.fragrans(I-H)and I.rotunda-I.rotunda(I-I).Then,all the combinations were subjected to waterlogging treatment and controlled water treatment respectively for 8weeks.During the experiment,we observed the morphological changes of every part of plants,and measured the biomass,root morphology indexes as well as non structural carbohydrate(NSC)contents every 2 weeks.The main research results are as follows:(1)Morphologically,in the process of waterlogging stress,all combinations of I.rotunda had been observed no wilting phenomenon,and the length of the underground parts of I.rotunda in I-R and I-M in the horizontal direction were significantly greater than that of the other two types.Among the heterogeneous plants,the drooping-speed and the most obvious performance of the H.fragrans were the fastest and the most obvious under the waterlogging stress,and M.exotica’s leaf had wilt.Conversely,there was no wilt symptom on R.simplex.(2)In terms of dry weight,the growth indexes of I.rotunda in I-R,I-I and I-H types were significantly different from those of other combinations under waterlogging condition,respectively.After waterlogged for 2 weeks,the mean growth value of I.rotunda in the I-R was the highest among the four types of I.rotunda,and there was a significant difference from other types(P<0.05).I.rotunda in I-I was the highest of the four types of I.rotunda after waterlogged for 4 weeks,and was significantly different from other types(P<0.05).In most of the time,the biomass indexes(i.e.leaf dry weight,stem dry weight,root dry weight and total dry weight)of I.rotunda in the I-H were the lowest among all the combinations,with significant differences from other types(P<0.05).But at the end of the waterlogging,there was no significant difference between the types.Among the three heterogeneous plants,the biomass index of H.fragrans under waterlogging stress decreased most significantly,followed by that of M.exotica,and the biomass of R.simplex under the waterlogging treatment decreased most slowly.(3)In terms of relative competition intensity(RCI),the facilitation effect of the combination of heterogeneous plants on I.rotunda decreased in order of herb,shrub and tree,among which the heterogeneous trees had obvious competition effect on I.rotunda.(4)In terms of root growth,in the four combinations of I.rotunda,the values of general root morphology indexes of the I-R were significantly different from the other three types in the early stage of waterlogging(P<0.05),but not significantly different from the other types in the later stage.The tissue density of the I-H was significantly lower than that of the other three types,and the other indexes were not significantly different from other types.There was no significant difference between the I-I and I-M except some indicators.The difference between different combinations of I.rotunda was mainly reflected in the fine root level,but not in the thick root level.Waterlogging stress had little inhibition effect on the growth of root system of R.simplex and I.rotunda,and significant inhibitory effect on the growth of root system of M.exotica and H.fragrans(P<0.05).(5)There was no significant difference in both roots and leaves of I.rotunda among different combinations of NSC.Waterlogging stress had significant effects on all plants(P<0.05).(6)In general,different root configuration combinations had significant effects on the growth of I.rotunda under waterlogging stress,especially on the biomass distribution of its leaves and roots,and the change of fine root morphology,but not on its NSC content.At the same time,waterlogging stress also had significant effects on biomass,root morphology and NSC content of all experimental plants.In conclusion,the growth status of I.rotunda under waterlogging stress decreased in the order of "herb-homogeneous species or shrub-heterogeneous tree",but the influence of plants on I.rotunda decreased with the increase of waterlogging time.The waterlogging tolerance of the group heterogeneous plants also descend in the order of "herb-shrub-heterogeneous tree".