| Content: There has been the urgent problem of Pinus massoniana woodland erosion andland degradation in red soil regions of southern China. The lack of understory vegetationis the primary and direct reason for the erosion in Pinus massoniana woodland. Plantcomposition and distribution of forest community is not only associated with thebiological characteristics, habitat conditions of plants, but also allelopathy effect of forestsystem. By collecting Pinus massoniana and Liquidambar formosana rhizosphere soiland using organic extraction, GC-MS and biological detection technology, this thesisdiscusses the chemical composition of Pinus massoniana root exudates, the allelopathiceffect, and the effects on the composition and distribution of understory vegetation. Theresults of the study are helpful to explain the present situation of the lack of Pinusmassoniana understory vegetation, and select the pioneer plant for underwood planting.It provides basic data and scientific foundation for targeted Pinus massoniana understoryvegetation restoration work. The main results are showed as follows:1. Chemical composition of Pinus massoniana root exudatesPinus massoniana and Liquidambar formosana root exudates contain respectively109and96components by using ethanol, respectively27and40kinds of organiccompounds which relative contents are more than0.6%. There are respectively56and63components by using ethyl acetate, respectively26and30kinds of organic compoundswhich relative contents are more than0.6%. Those organic compounds containhydrocarbons, alcohols, aldehydes, ketones, acids, esters, phenols and amide, amongwhich each extracts organic acids constitute the largest share. The content of pure forestis obviously higher than mixed forest. Therefore, in terms of the amount and thecategories of components, ethanol extraction performs better than ethyl acetate. Thehighest content of ethanol or ethyl acetate extraction of Pinus massoniana root exudatesis dehydroabietic acid, up to28.98%. Pinus massoniana contains eight timesdehydroabietic acid more than Liquidambar formosana.2. Allelopathic effect of Pinus massoniana root exudatesThe allelopathic effect of Pinus massoniana root exudates on four receptor plants isinhibition which contains three types: without obvious concentration effect, with higherconcentration and higher effect, and with higher concentration and lower effect. Theintensity of inhibition effect: pure forest of Pinus massoniana> mixed forest ofLiquidambar formosana. However, the root exudates of Liquidambar formosana havedifferent degrees of inhibiting or promoting effect on receptor plants in differentconcentrations. The allelopathic effect index of Pinus massoniana on four receptor plants: (ⅰ) Cynodon dactylon: root length> shoot height> dry weight> germination index>germination rate,(ⅱ) Trifolium repens: root length> germination index> dry weight>shoot height> germination rate,(ⅲ) Paspalum notatum: root length> dry weight>germination rate> germination index> shoot height,(ⅳ) Poa annua: root length>germination index> germination rate> dry weight> shoot height. The root length offour receptor plants is more sensitive to Pinus massoniana root exudates.3. Allelopathic effect of Pinus massoniana organic acid allelochemicalsThree kinds of organic acid on four kinds of receptor plant growth indexes(germination rate, root length, shoot height, dry weight) has certain inhibitory effect, butthe restrain power degree of receptors vary with the different concentration. Theallelopathic strength of organic acids on the same receptor plants:(ⅰ) cynodon dactylon:dehydroabietic acid> palmitic acid> stearic acid,(ⅱ) Paspalum notatum:dehydroabietic acid> stearic acid> palmitic acid,(ⅲ) Setaria viridis: stearic acid>palmitic acid> dehydroabietic acid,(ⅳ) Pennisetum alopecuroides: dehydroabieticacid> palmitic acid> stearic acid. The allelopathic strength of the same organic acid onthe receptor plants:(ⅰ) dehydroabietic acid: Pennisetum alopecuroides> Setariaviridis> Paspalum notatum> cynodon dactylon,(ⅱ) stearic acid: Setaria viridis>Paspalum notatum> Pennisetum alopecuroides> cynodon dactylon,(ⅲ) palmitic acid:Setaria viridis> Pennisetum alopecuroides> Paspalum notatum> cynodon dactylon.4. Effect of Pinus massoniana root exudates on soil micro ecological environmentPinus massoniana root exudates have positive effect on improving soil microecological environment, but the effect intensity significantly is less than the mixedforests. Soil pH is reduced, and the soil organic matter and available nitrogen is increased.It has inhibitory effect on soil catalase and phosphatase activity, and the mixed forestshow accelerating effect. And has no influence on soil urease, soil invertase activityshowes obvious role in promoting. In addition, the root exudates of the pure forest ofpinus massoniana and mixed forest has positive effect on soil bacteria, fungi andactinomycetes, but the intensity is less than mixed forest. Therefore, soil physical andchemical properties, enzyme activity and microorganism amount had a certain influenceon the ecosystem productivity, soil phosphatase and catalase activity of them are theimportant factors influencing the soil micro ecological environment.In conclusion, the pinus massoniana root exudates have certain impact oncomposition and distribution of the understory vegetation which include allelopathy onsurrounding plants and influence on soil micro ecological environment. Exploring thecurrent situation and cause of the soil and water loss, and lack of pinus massonianaunderstory vegetation has positive meaning from the perspective of allelopathy. |
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