| Eucalyptus(Eucalyptus spp.)has developed rapidly in southern China in the past two decades because of its rapid growth and good economic benefits.however,with the continuous high-intensity short rotation management and mountain refining management of single eucalyptus species,a series of problems such as gradual decrease of soil fertility,decline of soil fertility,serious soil erosion and so on.The study shows that the new forest management model with no mountain refining,simplification and less disturbance is one of the important measures to solve the above problems.How to respond to the soil physical and chemical properties and soil enzyme activity of eucalyptus plantation under the new silviculture model?What are the characteristics of heavy metals in woodland soil under the new forest management model?What is the relationship between soil nutrients,enzyme activities and heavy metal elements under the new model?In order to explore the above problems,the new afforestation experiments of eucalyptus with three different cutting residues and three different types of fertilizer treatments were established in the main producing areas of eucalyptus in Guangxi.Using randomized block design,compound fertilizer,organic fertilizer and inorganic fertilizer were set up on the basis of paving,removing and stacking of cutting leftovers.The soil physical and chemical properties,enzyme activities and soil heavy metals in different seasons(rainy season and dry season)were observed,and the adjacent secondary evergreen broad-leaved forest was used as control.By using the methods of principal component analysis,redundancy analysis and structural equation model,this paper discusses the change law of soil properties in different seasons under the new forest management mode,so as to provide a theoretical basis for the mountain-free forest management model of eucalyptus plantation.The main conclusions are as follows:(1)Under three different cutting residue management measures,the soil bulk density of eucalyptus woodland under tiling treatment was significantly lower than that of removal and stacking,thus improving soil quality.Under the tiling treatment,the bulk density of eucalyptus plantation was smaller,and the other physical indexes had no significant difference among groups,and the soil nutrients of evergreen broad-leaved forest were significantly lower than those of eucalyptus woodland.Soil electrical conductivity,available potassium,total potassium,total phosphorus,ammonium nitrogen and nitrate nitrogen were higher than other treatments,and eucalyptus woodland was higher than evergreen broad-leaved forest.The results showed that under the treatment of tiling and stacking,the return of cutting residue nutrients made the activity of soil microorganisms stronger,thus promoting the decomposition of total nutrient elements in soil and accelerating the absorption of available nutrients by eucalyptus.(2)Under tiling treatment,the activities of catalase and acid phosphatase in soil were higher than those in removal and stacking treatment,which indicated that tiling treatment accelerated the decomposition rate of cutting residue,promoted the nutrient release of litter,and increased the content of soil organic matter.it is beneficial to the nutrient absorption and growth of eucalyptus woodland.However,the nutrients released by the cutting residues were not enough to maintain the normal growth of the stand in the early stage,so the soil enzyme activity was generally lower than that of the secondary evergreen broad-leaved forest.The results showed that there was a very significant correlation between soil acid phosphatase activity and soil acid phosphatase activity(p<0.01).(3)Under the No-burning treatment,the soil heavy metal content of eucalyptus plantation did not exceed the standard and there was no significant difference between the two seasons(p>0.05),and the soil heavy metal content of eucalyptus forest did not increase significantly.According to the individual pollution grade and comprehensive pollution grade obtained by single pollution index and Nemero comprehensive pollution index(Table 3.3.8),the content of heavy metals in all places did not exceed the standard and was in the safety grade.(4)Fertilization treatment was significantly correlated with soil electrical conductivity,available potassium,total nitrogen and ammonium nitrogen content(p<0.05);soil catalase activity,urease activity and acid phosphatase activity in evergreen broad-leaved forest were significantly higher than those in eucalyptus forest,while sucrase activity was organic fertilizer>compound fertilizer>inorganic fertilizer>evergreen broad-leaved forest.The contents of chromium,iron and lead in soil with organic fertilizer were significantly higher than those in other treatments and evergreen broad-leaved forest.Under the condition of the same amount of fertilizer,the application of organic fertilizer had the greatest effect on the soil fertility of eucalyptus forest,followed by inorganic fertilizer.Under the action of inorganic fertilizer and organic fertilizer,the soil pH value of eucalyptus woodland was significantly improved(p<0.05).Compared with the control,fertilization could increase the activities of soil urease and acid phosphatase,but inhibit the activity of catalase.The high contents of chromium,iron,lead and strontium in soil appeared under organic fertilizer treatment,and there was a very significant correlation between fertilization treatment and soil iron and lead content(p<0.01).(5)The statistical method showed that there was a correlation between nonrefining mountain treatment and soil properties,and the tiling treatment had a higher nutrient cycling rate,which was beneficial to the nutrient absorption and circulation of eucalyptus plantation.The results of principal component analysis of soil chemical properties show that the degree of explanation of available elements to soil chemical properties is 41.1%,and that of total elements is 20.7%.The principal component scores of soil chemical properties of organic fertilizer and compound fertilizer are higher than those of evergreen broad-leaved forest.The results of redundancy analysis showed that redundancy 1 explained 15.41%of the change,and redundancy 2 explained 9.61%of the change,both revealing 25.02%variance.The results showed that there was a positive correlation between soil enzyme activity and soil total velocity(p<0.05),but a negative correlation between soil enzyme activity and soil available elements(p>0.05).Path analysis of structural equation showed that there was a direct positive correlation between soil chemical properties and soil heavy metal content,the correlation coefficient was 0.35(p>0.05),and there was a direct positive correlation between soil heavy metal elements and soil enzyme activity.the correlation coefficient was 1.06(p<0.01). |
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