Effects on Soil Polyphenol Oxidase Activities and Phenol Content of Eucalyptus Growing

【摘要】：With the productivity decline of the continuous-planting rotation in pure plantations in China,soil phenols were attracted more attentions by experts.In this paper,the variation and correlation of the soil polyphenol oxidase activity and phenols contents were analyzed in different continuous planting of Eucalyptus urophylla ×E.grangdi (first generation with two years old,first generation with five years old,second generation of two years old),which would be helpful to enrich allelopathy and provide reference for sustainable management of Eucalyptus plantations.The results were as follows: (1) The soil polyphenol oxidase activity showed higher in forest field than in rhizosphere,and had an increasing trend with the rotations of continuous planting raised.Soil polyphenol oxidase activity in the two-year-old plantations of second generation was the highest (1.299μg·g-1h-1).The reason might be that some environment ecological factors (such as climate,soil,animalcule or allelochemicals) were changed by the replanted pure plantations.Soil polyphenol oxidase activity was increased to adapt to changes.(2) The total phenols and complex phenol showed higher in rhizosphere than in forest field soil.The accumulation of phenols in rhizosphere was relevant to microbial ferment solution,organic compounds decomposition and root exudation.The declined trend of phenols content with the depth of soil was relevant to soil leaching.The two species of phenols had a decreasing trend with the rotations of continuous planting.It proved that the accumulation of phenols was not cause by successively planting Eucalyptus.In addition,non-free phenols were harmless to plants and soil.(3) Water-soluble phenol showed higher in forest field than in rhizosphere,and had an increasing trend with the rotations of continuous planting.Water-soluble phenol is one kind of the allelochemicals in soil which causes damage to plants.But it does not reach the toxicity level as its low content (0.622~3.39μg·g-1).Moreover,Water-soluble phenol is easy to be transformed into complex phenol.It will be further studied that Eucalyptus were stimulated or suppressed by the level of Water-soluble phenol.(4) The soil polyphenol oxidase activity was correlated negatively with total phenols,complex phenol,and positively with water-soluble phenol.It was approved that the degradation of phenols were caused by polyphenol oxidase.Furthermore,the pH value of soil(4.6~6.1) had significant positive correlation with the soil polyphenol oxidase activity and Water-soluble phenol,and negative correlation with total phenols and complex phenol.