| Korean pine and broadleaved species mixed forest is a zonal forest vegetation in the eastern mountain area of Northeastern China.Forest gap is an important small-scale disturbance in the forest system.It has different effects on photosynthetic effective radiation,temperature,relative humidity and other factors in different positions,as well as the changes of soil physical and chemical properties,nutrient resources and availability.Phenolic acids released by litter decomposition are common secondary metabolites of plants in ecosystems,and their accumulation in soil has great influence on soil fertility decline and plant growth and regeneration.The influence of phenolic acids accumulation in soil on decline of soil fertility,growth and renewal of plants can not be ignored.Previous studies have found that the growth of Korean pine seedlings is difficult to maintain for more than ten years in Korean pine and broadleaved species mixed forest.Scientific researchers have carried out a comprehensive study on this phenomenon from tree species proportion,stand structure,nutritional relationship and other aspects,but the research is mainly based on aboveground plant ecology.This study focused on the underground ecology to explore the effects of phenolic acids released from litter decomposition on the growth and regeneration of Korean pine.In this study,the research objects were litter(Tilia amurensis,Pinus koraiensis,Betula costata)and soil under litter decomposition bags in Korean pine and broadleaved species mixed forest gaps(large forest gap,middle forest gap,small forest gap)of Liangshui National Nature Reserve.We explored the method of separating phenolic acids by high performance liquid chromatography(HPLC),studied the characteristics of migration and change of phenolic acids content in litter and soil during the decomposition process,analysed the relationship between soil phenolic acids content and soil nutrients content,and tested the effects of several main phenolic acids on the seed germination and seedling growth of Korean pine.It provided basic data and theoretical support for the regeneration of mixed broadleaved Korean pine forest.The main results were as follows:1.The best gradient elution procedure for the determination of phenolic acids by HPLC was 0?15 min,30%A/70%B?50%A/50%B;15?20 min,50%A/50%B?55%A/45%B;20?30 min,55%A/45%B?60%A/40%B.The optimized detection conditions were as follows,detection wavelength was 280 nm,eluent was methanol water solution(0.1%phosphoric acid),flow rate was 1ml/min,column temperature was 25?,injection volume was 15 ul.The phenolic acids in litter and soil under litter decomposition bag of Korean pine and broadleaved species mixed forest were identified by optimized HPLC.There were 13 species of phenolic acids,including gallic acid,protocatechuate,chlorogenic acid,4-hydroxybenzoic acid,vanillic acid(VA),syringate acid(SA),vanillin,p-hydroxycinnamic acid,ferulic acid,coumarin,benzoic acid,cinnamic acid,salicylicacid.The contents of p-hydroxybenzoic acid,vanillic acid,syringate and benzoic acid(BA)were significantly higher than those of other phenolic acids.The initial contents of phenolic acid in Tilia amurensis,Pinus koraiensis,Betula costata litter were significantly different.The content of phenolic acid in Korean pine litter was significantly higher than that in Tilia amurensis and Betula costata litter.The total content of phenolic acid in three litters decreased with litter decomposition.The total content of phenolic acid in soil under litter decomposition bags increased as a parabola with litter decomposition.The content of phenolic acid in soil was generally middle forest gap>small forest gap>large forest gap.The ability of large forest gap soil to regulate phenolic acid was stronger than small forest gap and middle forest gap.In the process of litter decomposition,a large amount of gallic acid,protocatechuic acid,p-hydroxycinnamic acid,ferulic acid,coumarin,cinnamic acid and salicylic acid were released from litter,but they had no significant effect on corresponding phenolic acid content in soil under litter decomposition bag.4-hydroxy benzoic acid,VA,SA,salicylic acid and BA in soil were significantly affected by the release of phenolic acid from litter decomposition.The gap size,litter decomposition time,litter species and interaction of all factors had significant effects on phenolic acid content(P<0.05).Litter species had the most significant impact on the change of phenolic acid content in the process of litter decomposition.Gap size had the most significant impact on the change of phenolic acid content in soil under litter decomposition bags.2.There was a certain correlation between soil phenolic acid and soil nutrient content under litter decomposition bags in different gaps,and the correlation degree was related to phenolic acid species,gap size and soil nutrient composition.The interaction effect between soil phenolic acids and soil nutrients could not be ignored.The correlation between the contents of 12 species of phenolic acids and soil nutrients in middle forest gap was generally higher than that in large forest gap and small forest gap.The change of soil nutrient content in different gaps had different effects on phenolic acid content,and the main factors affecting the content of phenolic acids were not the same.3.Different concentrations of BA,SA,VA and mixed solution inhibited seed germination of Korean pine.The germination percentage,germination potential and germination index of each treatment group were lower than those of control group,and the germination potential and germination index were not significantly affected by change of phenolic acid concentration.Different concentrations of BA,SA,VA and mixed solution had no significant effect on the growth of hypocotyl and radicle of Korean pine seed.The interaction effect of mixed phenolic acid solution was stronger than that of single phenolic acid solution,and the effect of phenolic acid solution on seed germination potential of Korean pine was stronger than that of germination percentage and germination index.BA,SA,VA and mixed solution interaction all inhibited the increase of seedlings height and ground diameter of Korean pine.The effect of concentration change of treatment solution on seedlings height and diameter was not significant.BA&SA&VA solution promoted the seedlings height of Korean pine,and inhibited the increase of ground diameter.3 species of phenolic acids and their mixtures solution inhibited the increase of seedlings biomass of Korean pine,and there was significant difference in biomass between different concentrations(P<0.05).The inhibition of phenolic acid solution on stem dry weight accumulation was stronger than root dry weight accumulation.The changes of phenolic acid concentration had different effects on content of photosynthetic pigment in the seedlings needle of Korean pine.Different concentrations of BA and SA&VA solution inhibited the production of photosynthetic pigment,while 200 mg/L SA,BA&VA,2 mg/L VA,BA&SA,2 mg/L VA and 20 mg/L VA&S A&VA promoted the production of photo synthetic pigment.The activity of antioxidant dismutase(SOD)in seedlings needle of Korean pine treated with different concentrations of phenolic acid solution increased slightly,while the activity of peroxidase(POD)and catalase(CAT)decreased significantly,and the content of malondialdehyde(MDA)and free proline increased significantly.At the same time,the changes of phenolic acid concentration had significant effects on antioxidant enzyme index,MDA and free proline content(P<0.05).The content of soluble protein and soluble sugar were significantly affected by variety and concentration of phenolic acid in seedlings needle of Korean pine.The content of soluble protein in seedlings needle treated with 2 mg/L BA&SA was higher than that in other treatments,and the content of soluble sugar in seedlings needle treated with 200 mg/L BA was higher than that in other treatments.Different concentrations of phenolic acid and mixed solution had allelopathy inhibition on seeds and seedlings of Korean pine.In conclusion,3 species of litter in different gaps of Korean pine and broadleaved species mixed forest decomposed and released phenolic acid into soil,which affected the content of phenolic acid in soil through migration or transformation.The change of phenolic acids content were mainly affected by gap size.Meanwhile,the content of phenolic acid in soil was closely related to soil nutrient content.Indoor simulation test verified the effects of single phenolic acid and the interaction between phenolic acid on seed germination and seedling growth of Korean pine.The results of this study provide some basic data for further understanding allelopathy mechanism of phenolic acids and the study of plant growth and regeneration in gaps of Korean pine and broadleaved species mixed forest,and also provide data reference for solving regeneration obstacles of Korean pine and scientific management of Korean pine and broadleaved species mixed forest. |
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