The Study On Allelopathy Of Populus Tomemtosa And Effect On Growth And Physiology Of Phenolic Acids On Its Own Seedlings

This paper through the outdoor potted plant trials, the allelopathic potential of Populus tomentosa was tested against its own seedlings in the growth with aqueous extracts obtained from different organs and soil of P.tomentosa. And the content of mainly 8 phenolic acids was determined in root, branchlet, fresh leaves, litters and soil with high performance liquid chromatography (HPLC). Then, we studied the effect of 8 phenolic acids on radicel growth of P.tomentosa. Last, we conduct the physiological impacts of both 4-Hydroxybenzoic acid and cinnamic acid on seedlings of P.tomentosa via the outdoor potted plant trials. The main results were showed as follows.1. The aqueous extracts of various organs (root, branchlet, fresh leaves, litters) and surface soil, inhibited the growth of seedlings height, basal diameter and activity of root, and the weights of root, stem and leaves of the seedlings, except that both branch and soil aqueous extract at 0.01 g·ml^-1 accelerated the growth seedling height and basal diameter, and root aqueous extract at 0.01 g·ml^-1 increase the seedling height slightly.The inhibited action on P.tomentosa seedlings was gradually intense with increasing concentrations. The inhibited effects of extracts of various organ and surface soil on growth increased in the order of surface soil, root, branch, fresh leaves, litters.2. 4-Hydroxybenzoic acid, pyrocatechol, salicylic acid, syringic acid,ρ-coumaric acid chlorogenic acid, ferulic acid and cinnamic acid were all determined in root , branch, fresh leaves and litters of 8 years old P.tomentosa, and the contents of the 8 total phenolic acid were separately 1060.97,896.48,1191.23,1325.90μg·g^-1 . The contents of cinnamic acid,pyrocatechol and salicylic acid were higher in roots and branch, account for 42.71%, 13.83% and2.86% . The cinnamic acid, 4-Hydroxybenzoic acid and salicylic acid were more in fresh leaves and litters, account for 47.37%, 14.21% and11.46% in fresh leaves and 55.70%, 13.28%, 11.47% in litters.ρ-coumaric acid was least in every organs.3. The total content of 8 phenolic acids in fresh leaves kept positive correlation with tree age, the total content separately was 415, 1191.23, 1419.43, 1624.61μg·g^-1 in 1, 8, 20, 40-year-old. The quantity of cinnamic acid, pyrocatechol and pyrocatechol were more in 1 year old. The poplar of 8 years old contained more cinnamic acid, 4-Hydroxybenzoic acid and salicylic acid. Cinnamic acid, ferulic acid and salicylic acid were more in 20 years old. Cinnamic acid, salicylic acid and 4-Hydroxybenzoic acid were more in 45 years old.4. The main components were cinnamic acid, pyrocatechol and 4-Hydroxybenzoic acid in rhizosphere soil. During growing season, the content of total 8 phenolic acids in the rhizosphere soil presented a double peak curve, the peaks appeared on June and October, the content respectively were 954.51μg·g^-1 and 2132.24μg·g^-1 . Within the distance 100cm from trunk, the further levels distance, the fewer the total content was. And at the distance of 25cm from trunk, with the increasing depth, the content of total 8 phenolic acids gradually reduced. Content of phenolics acid in soils was far fewer that of the rhizoshere soil.5. The result of bioassay indicated that the inhibition effect of 8 phenolics acid on growth of P.tomentosa seedling radicle was order of 4-Hydroxybenzoic acid>cinnamic acid>ferulic acid>pyrocatechol>salicylic acid>syringic acid>ρ-coumaric acid>chlorogenic acid.6. In a culture experiment, effect of the 4-Hydroxybenzoic acid and cinnamic acid at different concentrations (2.5, 5, 10 and 15mM) on the contents of malondialdehyde (MDA), activities of antioxidant enzymes and the cell membrane permeability in leaves of poplar seedlings were investigated. The results showed that, after exposure to the two allelochemicals, the contents of MDA and relative conductivity increased significantly, with increasing time and concentrations. The activities of superoxide dismutase (SOD) were decrease, with increasing concentrations, and it decreased at the initial period (5^-1 0 d) and then recovery(no reaching control level), with increasing time. Whereas the activities of catalase (CAT), increased when treated with these two allelochemicals at the concentrations of 2.5 and 5mM, but CAT decreased at 10 and 15 mM after treatment 20 d. The activities of peroxidase (POD) were decrease, with increasing concentrations of 4-Hydroxybenzoic acid, and it decreased at the initial period and then recovery at the later period, with prolonging time. The activities of peroxidase (POD) were increase at 2.5mM cinnamic acid after treatment 5 and 10 days.7. The results showed that, the contents of ABA were increased, but the contents IAA,ZR,GA₃ were decreased. At lower concentrations(2.5mM and 5mM), ABA content increased at the initial period and then recovery at later period with prolonging time, whereas the time of ABA recovery exposure to the 4-Hydroxybenzoic acid was later than the cinnamic acid. At higher concentrations (10mM and 15mM) ABA content increased, with increasing time.At lower concentrations, ZR and GA₃ content were decreased at the initial period and then recovery at later period with prolonging time. But at higher concentrations ZR content decreased, with increasing time.IAA content decreased at the initial period and then recovery at later period with prolonging time exposure to cinnamic acid. But IAA content decreased exposure to higher concentrations (10mM and 15mM) of 4-Hydroxybenzoic acid with prolonging time.8. The results showed that after exposure to the two allelochemicals, the contents of the contents of chlorophyll (CHL), net photosynthetic rate(Pn), Stomatal conductance (Gs), transpiration rate (Tr) declined significantly with increasing concentration, whereas the two allechemical has both inhibited and promoted effect on intercellular CO₂ concentration. At lower concentrations (2.5mMand 5mM), content of CHL, Pn, Gs and Tr were decreased at the initial period and then recovery at later period with prolonging time. But at higher concentrations (10mM and 15mM) content of CHL, Pn, Gs and Tr increased, with increasing time.9. Both 4-hydrobenzoic acid and the cinnamic acid affected the absorption and the utilization of the different organs of poplar seedling for the N, P, K, Ca, Mg major elements and the Fe, Mn, Cu, Zn trace element, particularly, at higher concentration. And 2.5mM cinnamic acid promoted the absorption of root and stem for the N. 2.5-5mM cinnamic acid promoted the absorption of leaves and stem for Cu. 2.5mM cinnamic acid promoted the absorption of root for the Fe, Mg.2.5mM 4-hydrobenzoic promoted the absorption of leaves and stem for Cu.