Effects Of Bamboo Density And Drought Stress On Photosynthetic Characteristics Of Five Medicinal Plants

Five medicinal plants including Polygonatum cyrtonema,Bletilla striata,Paris polyphylla,Tetrastigma hemsleyanum and Curculigo orchioides were used as test materials,and interplanted under the Phyllostachys edulis forest with non-woven bags.Three bamboo forest density gradients(LD,1800-2100 plants·hm^-2;MD,2100-2400 plants·hm^-2;HD,2400-2800 plants·hm^-2)and holding water 7 d（LS）,14 d（MS）,21 d（SS）.Under different test conditions,the leaf pigment content,light response curve and chlorophyll fluorescence characteristics of 5 medicinal plants were analyzed,and the response mechanism of light response curves and chlorophyll fluorescence characteristics to different bamboo density and drought stress was explored.The research on bamboo density regulation and stress-resistant cultivation provides theoretical basis for interplanting medicinal plants under the Phyllostachys pubescens forest.The main findings are as follows:1.The Chl a,Chl b and Chl t of B.striata,P.polyphylla,T.hemsleyanum and C.orchioides increased with the increase of bamboo density.There was no significant change in leaf pigment content of P.cyrtonema.The Chl a/b ratio of B.striata,T.hemsleyanum and C.orchioides decreased significantly under high density bamboo forest.After drought stress,Chl a,Chl b and Chl t decreased significantly,and Chl a/b ratio（except B.striata）decreased significantly.2.The AQY of B.striata,T.hemsleyanum and C.orchioides reached the minimum under high density bamboo forest.The P_maxof P.cyrtonema,P.polyphylla and T.hemsleyanum reached the maximum under the medium density bamboo forest.The P_maxof B.striata and C.orchioides under low density bamboo forest was significantly higher than that of other treatments.After drought stress,AQY,P_maxand R_dof the five plants showed a downward trend,while under mild drought,AQY and P_maxdecreased slightly;under moderate drought,AQY decreased by B.striata<P.cyrtonema<P.polyphylla<T.hemsleyanum<C.orchioides,P_maxdecreased by B.striata<P.cyrtonema<C.orchioides<T.hemsleyanum<P.polyphylla;under severe drought,AQY and P_maxdecreased rapidly.P.cyrtonema,T.hemsleyanum and C.orchioideslsp decreased first and then increased;P.cyrtonema and T.hemsleyanumlcp decreased first and then increased;LCP of B.striata,P.polyphylla and C.orchioides increased gradually with the aggravation of stress.3.The results showed that the Fv/Fm of PSⅡin P.cyrtonema and B.striata did not change significantly;the Fv/Fm of P.polyphylla and T.hemsleyanum reached the minimum under low density bamboo forest;Fv/Fm of C.orchioides reached the maximum value under low density bamboo forest.The results showed that P.polyphylla and T.hemsleyanum reached the maximum values of Y（II）and relative electron transfer rate（ETR）of PSⅡunder medium density bamboo forest,while Y（II）and ETR of P.cyrtonema,B.striata and C.orchioides reached maximum under low density.After drought stress,fo and NPQ increased,Fm,Fv/Fo,Fv/Fm,Y（II）,QL and ETR decreased.Y（NPQ）first increased and then decreased with the increase of drought degree,while Y（NO）trend was opposite.Y（NO）increased rapidly in severe drought.Under drought stress,Fv/Fo and Fv/Fm of B.striata decreased the least,C.orchioides decreased the most.4.With the aggravation of drought,the O,K,J points of the OJIP curve of the five plants increased,while the P points decreased.The fluorescence quantum yield related parametersφP_o,ψ_o,andφE_oshowed a downward trend,whileφD_oincreased.The specific activity parameters such as ABS/CS_O,TR_O/CS_O,ET_O/CS_O,DI_O/CS_Oand other specific activity parameters and quantum yield parameters all reflected the decline of photosynthetic performance after drought stress.The PI_ABSof five plants showed a significant downward trend,and were more sensitive to stress than other indicators.Under severe drought of P.cyrtonema,B.striata,P.polyphylla,T.hemsleyanum and C.orchioides,PI_ABSdecreased by 47.80%,63.29%,69.62%,92.96%and 96.50%respectively compared with CK.In conclusion,the photosynthetic performance of five medicinal plants under high density bamboo forest is poor,while P.polyphylla and B.striata under low density bamboo forest are photoinhibited.The results showed that P.cyrtonema had a wide range of adaptability to the density of bamboo forest,and the utilization ability of strong light was the best under medium density;the photosynthetic performance of B.striata and C.orchioides increased with the decrease of bamboo density,which was suitable for interplanting under low density bamboo forest;P.polyphylla and T.hemsleyanum were suitable for interplanting under medium density bamboo forest.Under moderate drought,B.striata,P.cyrtonema and P.polyphylla increased the heat dissipation of antenna pigment,reduced the photosynthetic mechanism,reduced the dark respiration rate,reduced the consumption,and maintained certain photosynthetic capacity by regulating energy distribution;T.hemsleyanum and C.orchioides were irreversibly damaged in a moderate drought,resulting in non stomatal limitation;in severe drought,the photosynthetic performance of five plants declined seriously.