Influence On Soil Microorganism And Soil Enzyme Activity And Soil Nutrient Of Cutting Disturbance In Eucalyptus Grandis Plantation

In recent decades, the studies on disturbed ecosystems have been carried out frequently, especially on their ecological processes and their responses to the disturbances. For this reason, sustaining or recovering forest service functions is one of the current purposes for managing forest ecosystems. Eucalyptus have been broad planted in many south region of china as one of the three main plantation trees in the world, its economical values and social values have gained extended identity. At present, most cultivation area had already entered the stage of cutting for utilization of Eucalyptus grandis Plantation in Sichuan province. In this paper, Eucalyptus grandis Plantation of Hongya city was regarded as the research object. Through studied on soil microorganism, soil enzyme activities and nutrient content of plots in one year after cutting, to investigate the change of forest soil quality, and further to analysis the influence of soil change on natural regeneration in coppice forest. The result showed that;1. Cutting operation in the experiment area mainly aimed at tree stem of Eucalyptus. Preserving stump (under 5 cm) when cutting was used to regeneration of coppice forest, and after cutting, the plot still preserved shrub and herb. One year after cutting, seedling in coppice forest grew well, and its average growth height was up to 4.58 m, average ground diameter was 3.66 cm. Compared with the control forest, the felling of forest tree makes lighting increased and humidity decreased. In the plot, average temperature increased by 1.3℃and average soil moisture increased by 2.95% in 0-20cm layer.2. The quantity of soil microorganism mainly distributed in 0-20cm layer. Its vertical distribution was uniform, that is, the trend was surface layer(0-20cm)>middle layer(20-40cm)>under layer(40-60cm). The composing of soil microorganism were same, that is, the aerobic bacteria was the most, the actinomycetes took the second place, and the fungi was the least. The proportion of aerobic bacteria in total number reached more than 94%, described as the most important status in soil microorganism. Soil microbes in every plot had different seasonal distribution. The aerobic bacteria were the highest in autumn and the lowest in winter. The actinomycetes were the highest in spring and the lowest in winter. The fungi were the highest in autumn and the lowest in winter. Total microorganism, the quantity of aerobic bacteria, actinomycetes and fungi in cutting plot were more than the control land. Cutting disturbance was profit for soil microorganism, average number of number one and number two plot in 2007 increased by 29.20% and 14.83%, separately. At the same time, total microorganism, and the quantity of aerobic in number one plot was more than in number two plot, the reason for this was properly relate to different slash disposal methods.3. The activity value of sucrase, urease, posphatase and catalase in number one and number two plot were bigger than the control land. Compared with Q, the annual average enzyme activity vaule of sucrase, urease, posphatase and catalase increased by 30.05%, 13.90%, 32.13%, 17.73% in number one plot, and 21.60%, 4.48%, 3.85% and 3.28% in number two plot. Between number one and number two plot, the enzyme activity value in number one plot was 6.95%, 9.01%, 27.23% and 13.99% times higher than the value in number two plot. The results investigated that the cutting disturbance increased the enzyme activity value, especially the number one plot that reserving remainder had higher value and more profitable for the growth of seedling in coppice forest. The highest value of sucrase, urease, posphatase and catalase in every plot all appeared in July. The seasonal change of enzyme activity was uniform in all plots indicated that cutting disturbance had no influence on it. The vertical distribution of the enzyme activity was the same to the soil microorganism.4. The cutting disturbance had important effect on soil nutrient content and played active role to improve the soil quality. After cutting, 1)The soil pH value was strong acid (pH < 5), varied from 3.73 to 4.59. The pH value in number one and number two plot was slightly higher than the control land, the annual average value was 4.32, 3.93, 3.89, respectively; 2) The content of soil organic matter in number one and number two plot was 61.8% and 37.8% times more than the control land in surface layer, and the variance was significant; 3) Cutting disturbance increased the content of total N, total P and total K. These indexes of number one plot were 12.49%, 18.48% and 3.86% times more than the control land, and the variance of total N and total P was pole significant. 4) Compared with the control land, the content of hydrolyable N, available P and available K increased by 31.06%, 15.79% and 54.57%, respectively. The variance of total N and total P were significant and pole significant.5. In cutting plot, the soil microorganism and soil nutrient interacted with each other in great extent. The soil microorganism and soil nutrient in number one plot were positive correlated with each other and had big correlation coefficient. Except total K did not achieve significant with aerobic bacteria, actinomycetes, fungi and total microorganism, the other factors all achieved significant or extreme significant. The soil enzyme and soil nutrient interacted with each other in some extent. The variance level between total N, hydrolyable N, available K and sucrase, urease, posphatase all achieved significant and extreme significant. And the variance of the soil organic matter and posphatase also achieved extent significant. In all, soil posphatase correlated significantly with other factors of soil nutrient and catalase correlated lightly at the same time.6. Soil microorganism and soil enzyme activities were usually considered as measure standard of soil fertility. Through statistical analysis of multiple regressions was in order to approach the model and significance in cutting plot. The equations were as follows: Y₁=2.670+0.025 X₁-3.793X₂ + 3.801X₃-2.044X₄+0.020X₅ R²=0.955 Y₂=102.456-3.436X₁+61.324X₂+230.729X₃+22.193X₄+2.658X₅ R²=0.971 Y₃=337.900+6.020X₁-61.408X₂+81.419X₃+16.186X₄+0.0334X₅ R²=0.510 Y₄=2970.017+7.875X₁+5259.581X₂-1327.945X₃+89.566X₄-1.521X₅ R²=0.656 Y₅=58.054+1.028X₁-279.432X₂+13.037X₃-4.034X₄+0.793X₅ R²=0.955 Y₆=0.951+0.017X₁-2.482X₂+0.980X₃-0.525X₄+0.006X₅ R² =0.939 Y₇=23.163+0.020X₁-9.797X₂+10. 078X₃-2. 301X₄+0.132X₅ R²=0.837Y₁ delegate organic matter, Y₂ delegate total N, Y₃ delegate total P, Y₄ delegate total K, Y₅ delegate hydrolyable N, Y₆ delegate available P, Y₇ delegate available K; X₁ delegate sucrase, X₂ delegate urease, X₃ delegate posphatase, X₄ delegate catalase , X₅ delegate total microorganism.The above equations showed that: in cutting plots, the change of total soil microorganism, sucrase, urease, posphatase and catalase would have significant or pole significant effect on soil organic matter, total N, hydrolyable N, available P and available K. So these indexes could reflect the soil nutrient content accurately.