Research On Shade Tolerance And Heat Resistance Of Three Ground Cover Plants Including Petasites Japonica

In recent years,with continuous deterioration of urban environment,people have stricter requirements for the living environment;thus,it's extremely urgent to build ecotype garden city.Ground cover plants are characterized by short plant type,rapid growth and reproduction,easy to cover bare land,which other arbors and shrubs are short of;thus such plants become necessary landscaping plants for building ecological gardens.However,many ground cover plants have grown under shade environment,namely the bottom of phytocoenosium;moreover,they have to bear extreme high temperature weather in summer in urban cities.Therefore,it becomes quite significant to select such ground cover plants with shade tolerance and heat resistance.Petasites japonica(Sieb.et Zucc.)F.Schmidt.,Ligularia fischeri(Ledeb.)Turcz.and Farfugium japonicum(Linn.)Kitamura.are perennial herb ground cover plants of the composite family,whose floral leaves are of high ornamental value.But there are few researches and reports on the resistance of these plants home and abroad.The paper takes these three ground cover plants as experimental subjects and analyzes their ornamental index,morphological index(length,width of leaves,height of plants),chlorophyll content of blades and photosynthetic characters from the perspective of different shade process(0 %(control value),55 % and 75 % shade degree);besides,it also observes their plant manifestations under different high temperature stress time(0,6,12,24,36,48 h)and measures their chlorophyll fluorescene parameters and physiological & biochemical indexes.In addition,it conducts systematical research on their shade tolerance and heat resistance capability,so as to provide scientific evidences for later introduction & cultivation and application in the gardens.The research results are as follows:Petasites japonica,Ligularia fischeri and Farfugium japonicum have higher ornamental value and better plant morphology under the shade degrees of 0 %,75 % and 55 % respectively as well as higher maximum fluorescene(Fm),potential photochemical efficiency(Fv/Fo),maximal photochemical efficiency(Fv/Fm),photochemical quenching coefficient(qP)and PS II actual photochemical efficiency(?PSII)while lower minimal fluorescence(Fo)and non-photochemical quenching coefficient(qN).With augmentation of shade degree,among the three plants,Ligulariafischeri has the maximum amplification of content of blade chlorophyll a+b as well as decreasing amplitude of chlorophyll a/b,followed by Farfugium japonicum and Petasites japonica.Under the shade degree of 75 %,Petasites japonica has the minimum light compensation point,light saturation point and maximum net photosynthetic rate;while Ligularia fischeri has the minimum light compensation point and light saturation point while the largest maximum net photosynthetic rate;while Farfugium japonicum has the minimum light compensation point and light saturation point under 75 %shade degree while the largest maximum net photosynthetic rate under 55 % shade degree.Based on comprehensive analysis through membership function,the result shows that: the sequence of shade tolerance of the three ground cover plants is: Ligularia fischeri > Farfugium japonicum > Petasites japonica.According to observation on plant manifestation,Ligularia fischeri suffers the most serious heat disaster after high temperature process,followed by Petasites japonica and Farfugium japonicum.The leaf relative water content of the three plants decreases with increasing stress time,with decreasing amplitude of Ligularia fischeri > Petasites japonica > Farfugium japonicum.Petasites japonica and Farfugium japonicum have smaller amplification of leaf relative electical conductivity during high temperature stress period,without obvious changes;while Ligularia fischeri has smaller amplification in the beginning of stress period but has increased rapidly in later period.After temperature process,Petasites japonica and Ligularia fischeri witness a decreased MDA content while that of Farfugium japonicum goes upward.During high temperature stress period,the enzymatic activity changes of SOD and POD of the three plants all witness an increase and then a decrease;soluble protein level remains decrease-increase-decrease,and chlorophyll content decreases gradually.With augmentation of high temperature stress time,Fo and qN of the three plants gradually go up while Fm,Fv/Fo,Fv/Fm,?PSII and qP decrease gradually(qP of farfugium japonicum is higher than control value),which are substantially lower than control value.Based on comprehensive analysis through membership function,the result shows that: the sequence of heat resistance of the three ground cover plants is: Farfugium japonicum > Petasites japonica > Ligularia fischeri.