| Phenols are one of the important secondary metabolism products of plants. In these years, Soil degradation which is result from successive planting of forest and continuous cropping of corps is deemed to the focus by the agriculture and forestry workers. Much academician considered that soil degradation is result from the accumulation of phenols in soil. But some academician considers that phenols are not the cause of soil degradation, in contrast, some of phenols afford protection to the growth of plants. As the research continuously deepened, the function of phenols performed in forest ecosystem conversion gets more and more attention from peoples, and the discussion of its function that afford protection to or restraining the growth of plants has became more and more vehement. From the results of current study, tdudy on the phenols in plant and the effect mechanism of phenols on plant growth are more, but on the soil phenols are less, especially on multi-generation planting can or not cause accumulation of phenols, the current evidence is not sufficient, is still in debate.Forest ecosystem conversion is of vital importance for the managing of the forest ecosystem. In history, the natural vegetation of mid-subtropical mountain ecosystem was evergreen broad-leaved forest on the whole. But most natural forests were transformed into the artificial cultivated ecosystem—such as farmland, orchard, tea garden, economic forest, artificial forest, and others-which was result from the managing action by mankind such as disforest and reclamation, building plantation. It presented diversification of forest ecosystem conversion mode. Along with the increase of population and the development of economy in particular, the velocity and frequency of forest ecosystem conversion became faster and faster, the resources of natural forest reduce rapidly, and the forest ecosystem degraded seriously. The development scale enlarged day by day and the successive planting of plantation become increasingly serious for the needing of wood by people in particular, which has became the main forms of current forest ecosystem conversion mode.Base on those issues, chosing 4 forest ecosystem modes—naturally regenerated evergreen broad-leaved forest model, the old-growth Chinese fir model, abandoned natural regeneration Chiness fir model, planted second-generation Chinese fir model—built in Xiqin Teaching Forest Farm in Nanping City as the series of quadrats, and using located research in the field, this paper studied on the space-time change law of content of phenols, polyphenoloxidase activity, decomposition of phenols with soil in the process of Forest Ecosystem Conversion, and discussed the distribution of phenols in four space level of ecosystem—tree layer, shrub layer, herb layer and litter layer. At the same time, using artificial simulation technique, this paper studied on the variation of the content of phenols in the process of decomposition of forest litter, and the influence mechanism of soil nitrification and enzyme activity which influenced by the additional phenols. And then tried to reveal formation and work mechanism of phenols in the forest ecosystem and the mechanism of soil degradation in plantation, and provide scientific theory basis and practical guidance for sustainable management in managing plantation. The results were as follows:(1) In the soil of the 4 ecosystems of ecosystem conversion, the content of phenols in the depth of 020cm is more than 2040cm. The content of total phenol is largest, its range is 278.400～3012.976μg·g-1. The content of complex phenol is secondary, its range is 20.667～430.535μg·g-1. The content of water-soluble phenol is least, its range is 0.363～6.006μg·g-1. Along with the change of the season, phenols in soil is change too, the size order of total phenol with four season is Mar>Sep>Jun>Dec, the size order of complex phenol is Mar>Sep>Dec>Jun, the content of total and complex phenol's change is'high-low-high-low'. The content of water-soluble phenol became lower as the season change. The result of variance analysis shows that the content of total phenol, complex phenol and water-soluble phenol in each systems are every significant different, it shows that the soil phenols existed significant seasonal change.(2) From the annual average of soil phenol indexes, it shows that soil phenols—the total phenols and complex phenols in particular—will accumulate to a certain extent along the ecosystem conversion direction. As the increas of Chinese fir planted generation soil phenol will accumulate to a certain extent, and there was a significant or very significant difference of soil total phenols and complex phenols between various systems, but does not show such regularity from soil phenol indexes of a specific season, that may be related to the seasonal changes of soil phenol indexes. It shows that the soil phenol indexes of a specific season can not fully reflect the actual sitiation of phenols. So, we must determine the multi-season sample if want to get a comprehensive and scientific reflection of actual situation of soil phenols.(3) From the results of study we knows that the concentrations of water-soluble phenol what can be absorb by plant in various systems are low, its range is 0.364～6.006μg·g-1, doesn't reach the poisoned value—50μg·g-1. It shows that even though multi-generation planting will cause the accumulation of phenols—especially the total phenols and complex phenol—in the soil of Chinese fir, but it does not poision Chinese fir or can say the possibility of poision is every small.(4) From the annual average we knows that the activity of polyphenoloxidase and catalase shows the law of"high-low-high"in the process of ecosystem conversion. As the season change, polyphenoloxidase activity became active, catalase activity become lower at first but active afterwords. Catalase activity was most active in Dec and lowest in Jun.(5) From the results of correlation analysis of six phenol indexes, it shows that total phenols, complex phenol and water-soluble phenol were significantly and positively correlated. Polyphenoloxidase activity is negatively correlated with three phenols, and the correlation with water-soluble phenol reached a significant level. The correlation of phenols decomposition in soil, complex phenol, polyphenoloxidase activity, catalase activity is significant and positive. From the result of principal component analysis, four kinds of systems can roughly be divided into 3 categories, the first category is naturally regenerated evergreen broad-leaved forest, the soil phenol content is low. The second category is old-growth Chinese fir and abandoned natural regeneration Chiness fir, the soil phenol content is higher. The third category is planted second-generation Chinese fir, the soil phenol content is highest. It shows that along the ecosystem conversion, or as the increase of Chinese fir planted generation, the phenols in soil are accumulated to a certain extent.(6) Detecting the soil of four systems and found that there exist p-hydroxybenzoic acid, vanillic acid and ferulaic acid, but not exist cinnamic acid. The content of p-hydroxybenzoic acid is largest, its range is 2.233～19.589μg·g-1 , the content in second generation of planted Chinese fir system's 2040cm depth soil is less than 5μg·g-1, and others are more than 5μg·g-1.The content of vanillic acid is secondary, its range is 0.912～5.683μg·g-1, the naturally regenerated evergreen broad-leaved forest's is more than 5μg·g-1 , and others are less than 5μg·g-1 .The content of ferulaic acid is least, its range is 0.496～12.566μg·g-1, the content in old-growth Chinese fir soil is more than 5μg·g-1, and others are less than 5μg·g-1. The content of three phenylic acids in 020cm depth soil is larger than 2040cm. Along the ecosystem conversion direction, in 020cm and 2040cm depth soil, the laws of P-hydroxybenzoic acid, ferulic acid and vanillic acid content are complex, does not exist apparent refularity.(7) As the season changes, the decomposition of phenols in soil become weaker at first and stronger afterwords, the value is largest in Dec and least in Jun. There was a positive correlation between the decomposition of phenols and the activity of polyphenoloxidase and catalase, because the process of phenols decomposition is completed by the enzyme. If the enzyme is more active, the decomposition of phenols in soil is stronger.(8) Water-soluble phenol in tree layer of every systems is maimly distributed in branches and leaves. Water- soluble phenol in the root of naturally regenerated evergreen broad-leaved forest is large too, it is close to branches and leaves. The content of most system's Water- soluble phenol in shrub layer is larger as the higher of plant organs from ground. But the content of Water-soluble phenol in planted second-generation Chinese fir's shrub layer is fewer as the higher of plant organs from ground, it is maybe related to the difference between component of the shrub layer plants in planted second-generation Chinese fir and other system. Water-soluble phenol of herb layer is mainly distributed in the ground part, and the content of water- soluble phenol in ground part is 2 times more than the underground part. The content of water-soluble phenol in leaves of litter layer is larger than branches, and leaves'is 2 times more than branches'. The content of water- soluble phenol in leaves of litter layer in planted second-generation Chinese fir even is 9 times more than branches.(9) Studying the water-soluble phenol in leaf litter of Chinese fir, Phoeba bourne, Schima superba and Castanopsis kawakamii after separate decomposited 60 days, it will found that the content of water-soluble phenol in Phoeba bourne is least, it is 64.264μg·g-1, the content of water-soluble phenol in Schima superba is largest, it is 877.551μg·g-1, Chinese fir and Castanopsis kawakamii are in the middle, the content of them are 271.357μg·g-1 and 465.856μg·g-1. From the situation of mixed leaf litter decomposition of Chinese fir, Phoeba bourne, Schima superba and Castanopsis kawakamii, it will found that the decomposition rate of water-soluble phenol in Phoeba bourne is largest, which reaches 85.104% when decomposing 60 days. Using the leaf litter of Phoeba bourne, Schima superba or Castanopsis kawakamii mixing with Chinese fir leaf litter, it will found that when the mixture of Chinese fir and Phoeba bourne as a 1:3 ratio, the content of water-soluble phenol is lower than pure Chinese fir after decompose. It shows that with such a proportion mixed platation of Chinese fir and Phoeba bourne can reduce water-soluble phenol in litter, and then reduce water-soluble phenol in soil. But mixing three kinds of broad-leaves and Chinese fir does not basically exist significant interaction.The mixing decomposition can not play the role of effective mitigation with water-soluble phebol.(10) Studying the natural digestion rate of soil phenols in room temperature and cold storage, it would found that with the passage of time, the contents of total phenols, complex phenol, and water-soluble phenol in various systems are basically decreased gradually, it shows that soil phenols are in a constant process of decomposition without additional phenols. In cold storage the rate is lower than room temperature. It shows that low temperature inhibited natural digestion of total phenols in soil, and the difference between the state of room temperature and low temperature reached significant level. The impact of temperature on the natural digestion rate of complex phenol and water-soluble phenol in soil was not obvious. The natural digestion rate of complex phenol and water-soluble phenol of soil in different systems was quite different, and the difference reached significant level, however, there were no significant differences in water-soluble phenol of different systems. If the initial total phenol in soil was large, the natural digestion rate was large too. It can suppose that even if the initial content of phenol is large, it will come down soon if there is no phenol addition.(11) With the concentration of added p-hydroxybenzoic acid or protocatechuic acid increased, soil nitrification enhance at first and weaken afterwords. It is show that low concentration of p-hydroxybenzoic acid or protocatechuic acid will promote soil nitrification and high concentration will inhibit soil nitrification. When the concentration of added p-hydroxybenzoic acid reach 2.4μmol·ml-1 and protocatechuic acid reach 0.8μmol·ml-1, soil nitrification reaches the maximum. Adding 1.6μmol·ml-1 of cinnamic acid or ferulaic acid will inhibit soil nitrification, and this concentration of mixture mixing p-hydroxybenzoic acid, cinnamic acid and ferulaic acid will enhance the effect of inhibiting soil nitrification.It is show that a mixture of these three phenolic acids will enhance the inhibition of soil nitrification. Adding 1.6μmol·ml-1 of p-hydroxybenzoic acid, cinnamic acid, ferulic acid, protocatechuic acid will weaken the activity of polyphenoloxidase and catalase, and this concentration of mixture mixing p-hydroxybenzoic acid, cinnamic acid and ferulaic acid will not enhance the effect of inhibiting soil nitrification.
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