Research On Effects Of Exogenous Phenolic Acids On Physiological Characteristics And Rhizosphere Soil Environment Of Trichosanthes Kirilowii Maxim.

Trichosanthes kirilowii Maxim.belongs to the perennial cucurbitaceae Trichosanthes kirilowii herbaceous vine.It is a economic crop with characteristics,and has higher comprehensive development value and economic value.The Medicine and Food Characteristics of T.kirilowii has led to growing demand and expanding acreage.The continuous cropping obstacle is becoming more and more obvious,which has seriously affected its quality and yield.According to investigation,self-allelochemicals is one of the key factors to lead continuous cropping obstacle as the root exudate and leaf&stem extracts of T.kirilowii seedling can trigger allelopathic effect.There are many kinds of allelopathy has been identified from T.kirilowii leaf and stem which contains high portion of phenolic acid substance.However no report available yet regarding the specific mechanism of how phenolic acid lead to allelopathic on T.kirilowii.Therefore this experiment is adopting soil culture to investigate the impact of autotoxins as p-hydroxybenzoic acid?pHBA?,benzoic acid?BA?and cinnamic acid?CA?on the growing of T.kirilowii seedling.With the technology of HPLC?High Performance Liquid Chromatography?,the content of gibberellin?GA₃?,heteroauxin?IAA?,salicylic acid?SA?and abscisic acid?ABA?in T.kirilowii seedling has been measured.Such experiment with the aiming to figure out the effect mechanism of phenolic acid on T.kirilowii and further lay the theoretical foundation of the occurrence mechanism of T.kirilowii continuous cropping obstacle has provided solid scientific evidence to work out specific solution to relieve autotoxicity and has significant contribution to the improvement of T.kirilowii cultivation and sustainability of such industry both theoretically and practically.The specific results are as follows:1.Different concentrations of pHBA,BA and CA had different inhibitory effects on plant height,root length,fresh weight,root fresh weight,chlorophyll a,chlorophyll b,root activity and transpiration rate.After treatment with pHBA,plant height,root length,fresh weight,chlorophyll a,chlorophyll b and chlorophyll a+b were significantly inhibited,and the inhibition was enhanced with the increase of stress concentration.Among them,low concentration could promote root fresh weight and root activity.The inhibition of transpiration rate was the strongest at the concentration of 100-150mg/kg.After the treatment of BA,seedling plant height,fresh weight,root fresh weight,chlorophyll a,b,a+b and root activity were reduced,while transpiration rate and fresh weight were promoted at the concentration of 50-100mg/kg,which was slightly higher than the control group.After CA treatment,plant height,root length,fresh weight,root fresh weight and chlorophyll content were all inhibited,among which root activity was close to that of control group at50-100mg/kg concentration.2.Low concentration of pHBA can significantly increase the activity of SOD,POD and CAT,and reduce the content of MDA.However,as time goes on and with the increase concentration,antioxidant enzyme activity was inhibited and MDA content was also increased.BA showed the strongest inhibitory effect on SOD,POD and CAT activity among the three phenolic acids and increased the content of MDA.When treated with cinnamic acid for 7 days,the maximum MDA content of T.kirilowii leaves reached 7.43 times of that of the control group,and the inhibition rate of CAT activity was 53.51%.POD at 21 days was similar to that of the control group,which was close to the normal level.SOD activity at 21days reached a maximum decrease of 28.48%.3.Three phenolic acids alter the enzyme system and microbial community composition of rhizosphere soil of T.kirilowii.The effect of CA on catalase activity was higher than that of pHBA and BA,and was 1.18 times of the control group.Under the effection of three phenolic acids,the maximum inhibition rates of sucrase were 27.22%,49.51%and 57.91%,respectively.In terms of urease activity,the group treated with 50mg/kg pHBA had a promoting effect on urease activity,and then showed inhibition.The urease activity has been increased by 50mg/kg BA.and in the second cycle?20d?was lower than that of in the first cycle?10d?.The effect of CA on urease activity was more obvious in the first cycle.The structure and composition of the microbial community were all changed to different degrees after being treated with three phenolic acids,which inhabited the production of bacteria and actinomycetes and increased the reproduction of fungi.The results of correlation analysis show that there is a certain correlation between soil enzyme activity and microbial structure.4.HPLC determination of the contents of IAA,GA₃,SA and ABA in leaves of T.kirilowii revealed that GA₃,IAA and SA,which had promoting effects on plant growth and development,all decreased to different degrees after treatment with three phenolic acids.The maximum inhibition rates of the three phenolic acids on GA₃ were 44.64%,51.41%and52.55%,indicating that the duration of CA effect was shorter.After the treatment with phenolic acid,the low concentration of phenolic acid promoted the synthesis of IAA,and the plants themselves regulated the damage of allelopathy through this way.After a certain concentration,the content of IAA was significantly lower than that of the control group.The influence of CA on SA content was the most significant,followed by BA.ABA is a plant growth inhibiting hormone,and the three phenolic acids significantly increased ABA content and accelerated the aging process of plant leaves.In the three periods after the treatment with pHBA,the maximum ABA content decreased by 49.14%.The maximum ABA content after the treatment with BA was 2.43 times that of the control group,and the maximum ABA content after the treatment with cinnamic acid was 236.03% of the control group.