Effects Of Alternative Continuous Cropping Of Poplar Cultivars Alternative On Soil Ecological Environment And Allelopathy Of Exogenous Phenolic Acids

Continuous cropping on poplar plantation led to severe soil degradation, declination of stands productivity and deterioration of soil ecological envirionment. In the past, climate, soil, the community structure and function of plantation, changes of soil microorganism divisions and cultivation measures were studied for soil degradation,lacking of necessary studies on effects of cultivars alternative continuous cropping and exogenous phenolic acids . In order to further reveal the mechanism of soil degradation of continuous cropping poplar plantation, and to find feasible technology and method to maintain the forestland productivity, soil environmental condition of continuous cropping different poplar clones plantation in Ju County, Shandong, were analyzed,effects of alternative continuous cropping on soil ecological envirionment of poplar planation were studied and the allelopathic effects of phenolic acids on soil enzyme, soil microorganism and poplar seedlings were studied by adding exogenous phenolic acids were also studied. The results showed that:1. Soil ecological envirionment of alternative continuous cropping (ACC) were obvious more excellent than that of non-alternative continuous cropping (NACC): pH value of ACC were higher than that of NACC, which implyed that under ACC soil acidification was alleviated effectively. Soil organic matter content, bacteria amount, fungi amount, actinomycetes amount and total amount of soil microorganism of ACC forestland were higher than that of NACC, and so were the activity of soil urease, peroxidase, polyphenol oxidase, but the activity of catalase was the opposite.2. Ferulic acid (FA), benzoic acid(BA), p-hydroxybenzoic acid (PA), cinnamic acid (CA) and vanillin (VA) in the poplar planation soil were all detected by high performance liquid chromatgraphy (HPLC), and they all accumulated to a certain extent in soil, and as the poplar planting generation increased, the content of FA decreased, while that of BA and CA increased. Amount of PA was the highest, while that of CA was the lowest, total content of those five phenolic acids in second generation of black poplar plantation was the maximum, while that in third generation was relatively less than it and that in first generation of ACC was the minimum. The total content of those five phenolic acids were significant different among different continuous cropping models .3. Phenolic acids had an obvious allelopathic effect on soil microorganism. With the concentration of treated exogenous FA, CA and VA increasing, the amount of fungi first increased and then decreased, and with the concentration of BA increasing the amount of fungi regularly increased. The amount of fungi reached mixmum under the treatment of FA and VA at the concentration of 50μg.g-1 and udnder that of CA at the concentration of 100μg.g-1. While the concentration of FA, BA and CA increasing, the amount of actinomycetes first increased and then decreased, but PA and VA had an inhibitory effect on actinomycete, and the degree of inhibition strengthened as the concentration increased. The amount of ammonifiers significantly increased by adding FA, PA and VA, and all reached the mixmum at the cioncentration of 100μg.g-1 of those three phenolic acids. As to BA and CA, at the concentration of 200μg.g-1, the amount of ammonifiers was inhibited. The amount of cellulose decomposing bacteria were inhibited by FA, PA and CA, and stimulated by BA and VA. All those five phenolic acids inhibited nitrite bacteria greatly and caused the amount of it dramatically reduced and the inhibition effect of PA was the strongest while that of VA was the lowest.4. Those five phenolic acids had an obvious allolopathic effects on activity of soil enzyme. All the five exogenous phenolic acids inhibited significantly growth and development of urease under the concentration of 50μg.g-1, 100μg.g-1and 200μg.g-1, and extent of inhibition presented as CA > PA> FA>BA,which exhanced as concentration increased. Catalase activity raised under the same concentration of BA and PA as the above, and its activity increased with the concentration raised. But it increased slowly with the concentration of CA and VA growing and it was inhibited by FA at high concentration. Peroxidase activity increased by FA at the concentration of 50μg.g-1, and decreased at 100μg.g-1 and 200μg.g-1; but peroxidase activity decreased merely under 200μg.g-1 of BA and CA, and VA stimulated it under all concentrations and there existed no significant rule of PA on peroxidase activity. All those five phenolic acids inhibited polyphenol oxidase activity with concentration growing, and the range of inhibition degree was FA>BA>PA. Inbihition of VA is weaker under low concentration, but it is stranger than all other phenolic acids under high concentration.5. Treatment of exogenous phenolic acids formed a stress to poplar hydroponic seedlings. It caused dysfunction of cell membrane and resulted in damage to cell integrity. It also increased cell membrane permeability and relative electrical conductivity. The extent of damage to tissue strenthened while the concentration increasing. Root activity reduced under the all the phenolic acid treatments, the higher the concentration of pheolic acids, the greater the effect.