Effects Of Phenolic Acids Allelochemicals On Growth And Physiology In Rhododendron Delavayi Franch

Rhododendron delavayi Franch is the dominant species and group species in a nature reserve of Rhododendron in Guizhou Province,in which the natural regeneration of the Rhododendron community is very difficult.Natural regeneration can be divided into two important stages:seed and seedling growth.In order to find out factors that hamper the natural regeneration of the Rhododendron community,the project team studied the soil where R.delavayi Franch live in,and its undergrowth by HPLC from the point of phytochemistry.It was found that the soil of R.delavayi Franch was rich in phenolic acids both in its body and undergrowth.In order to investigate the response of seed germination and seedling growth of R.delavayi Franchto phenolic acids,the seeds and seedlings of R.delavayi Franch as the research objects were imposed to exogenous phenolic acid of different concentrations.The germination of seeds and the changes of morphological growth,photosynthesis,leaf stomata and physiological indexes were observed to analyze the influence of phenolic acid on seed germination,post-germinated radicle,seedling growth,biomass,and physiological parameters of R.delavayi Franch seedling leaves in the following aspects:gas exchange parameters,stomatal characteristics,antioxidant enzyme activity,membrane peroxidation products,osmotic regulators and chlorophyll.The main results of this study are as follows:1.Ferulic acid and eugenic acid inhibited the germination rate and germination potential of R.delavayi Franch seeds,while chlorogenic acid,caffeic acid,protocatechuic acid and gallic acid didn't before their concentrations exceeded 12.50,0.75,0.1 and 3.20 mg/L respectively.The allelopathic effects of the six phenolic acids were:gallic acid>chlorogenic acid>protocatechuic acid,caffeic acid>ferulic acid>syringic acid.2.After seed germination,ferulic acid,eugenic acid,protocatechuic acid,and caffeic acid all inhibited the elongation of the seed radical and embryo,and biomass accumulation of radicle and germ of Rhododendron mandshurica,which were not the case of chlorogenic acid and gallic acidyet.3.Ferulic acid,chlorogenic acid and protocatechuic acid at low and medium concentrations all inhibited the growth of R.delavayi Franch seedlings,and accumulation of its undergrowth and aboveground biomass.The medium concentration of ferulic acid,chlorogenic acid and higher concentration of protocatechuic acid inhibited the growth of the basal diameter of R.delavayi Franch seedlings,while the low concentration of protocatechuic acid and the high concentration of ferulic acid promoted the growth of ground diameter.4.Ferulic acid,chlorogenic acid and protocatechuic acid all improved the relative amount of chlorophyll a,chlorophyll b,total chlorophyll,and carotenoid in the seedlings of R.delavayi Franch.Low concentration of ferulic acid significantly inhibited stomatal opening,stomatal opening ratio,stomatal length and width;chlorogenic acid and ferulic acid of middle and high concentrations significantly inhibited stomatal density.Ferulic acid significantly inhibited the net photosynthetic rate and stomatal conductance of seedlings,so did chlorogenic acid;and the intercellular CO₂ concentration and transpiration of seedlings were significantly inhibited by chlorogenic acid of low and medium concentrations.Ferulic acid of high concentration significantly inhibited stomatal limitation,while protocatechuic acid of medium concentration significantly inhibited net photosynthetic rate,stomatal conductance and intercellular CO₂ concentration.5.Ferulic acid,chlorogenic acid and protocatechuic acid all inhibited and promoted POD and CAT of R.delavayi Franch leaves with the increase of treatment time.With different concentrations yet the same processing time,processed by three kinds of phenolic acid,the proline content were higher than the one of the control group,and no obvious change showed in soluble protein content;with the same concentration yet different processing time,the content of proline and soluble protein time decreased with the prolonged processing time in early processing period?10³0d?,but at the process stage of the 40^thh day,the content of proline and soluble protein increased significantly;MDA content increased gradually with the extension of the processing time.6.The content of chlorophyll a and carotenoid gradually increased with the lengthened processing with ferulic acid and chlorogenic acid,chlorophyll b and carotenoid content decreased and increased with the lengthened processing with protocatechuic acid respectively.The content of chlorophyll a and total chlorophyll increased first and then decreased with the prolonged processing with protocatechuic acid,but the change trend of chlorophyll b processed by ferulic acid and chlorogenic acid is opposite to the change of total chlorophyll processed by ferulic acid.When processed with three phenolic acids for 10 days,chlorophyll a decreased significantly,chlorogenic acid and protocatechuic acid promoted chlorophyll b and carotenoid significantly;and at the 30th and 40th day of process,the content of chlorophyll a,chlorophyll b,total chlorophyll and carotenoid were significantly lower and higher than the control group respectively.