| Rubber and Eucalyptus plantations, as the typically artificial forests, are widely cultivated in Hainan Island, both of these two plantations have an important influence on the stability of forest ecosystems and the sustainable development of soil ecosystems in this region. Soil active organic carbon and soil enzymes are important active components of soil ecosystem and have important theoretical significance for improving the potential productivity of soil and maintaining the circulation of material and energy of soil ecosystem. Therefore, it is often used to monitor soil quality of the important indicators.This study estimated the vertical distribution of soil organic carbon and nitrogen and soil enzymes activities with planting age and soil layer by combing with field sampling and indoor analysis and testing methods in Danzhou different ages rubber (5?10?15?20?25?year) and eucalyptus (2?4?6 year) plantation ecosystem, and the relationship between soil active organic carbon and nitrogen , soil enzyme activities and soil physical and chemical factors were studied in these two plantations. The aim of this study was to investigate the distribution of soil active organic carbon and nitrogen and soil enzymes in rubber and eucalyptus plantations, and the relationship between soil active components and soil physical and chemical factors. To monitor the ecosystem function of plantation, Status and sustainable use of land to provide data support, but also for the scientific management of plantation to provide a theoretical basis.The main results are as follows:1 The range of the content of soil microbial biomass carbon in Rubber plantation of different age was 7.81?172.20 mg·kg-1,and Soil microbial biomass nitrogen was 1.91?16.17mg·kg-1,and dissolved organic carbon was 3.17?80.32 mg·kg-1, and dissolved organic nitrogen wasl3.72?27.67 mg·kg-1. And the range of the content of soil microbial biomass carbon in Eucalyptus plantation of different age was 5.03?91.83 mg·kg-1, and Soil microbial biomass nitrogen was 0.60?10.68 mg·kg-1, and dissolved organic carbon was 10.96?42.94 mg·kg-1, and dissolved organic nitrogen was4.91?10.65 mg·kg-1. The contents of activity of organic carbon and nitrogen in the soils of Rubber plantation and Eucalyptus plantations showed that the shorter planting time plantations were higher than those of plantations with longer planting years. Within the soil depth of 1 meter, the content of organic matter in both of Rubber and Eucalyptus plantation soils showed the same tendency to decrease with the soil layer. The vertical distribution of the four active organic matters in Rubber and Eucalyptus plantation also had obvious surface aggregation characteristics, that is, the content of active organic carbon and nitrogen is concentrated in the surface 0-10cm of soil. In Rubber plantations, the contents of MBC, MBN, DOC and DON accounted for the soil profile proportion of 29.69%?43.80%, 27.54%?36.60%,26.90%?40.02% and 30.60%?49.24%. And in the 1m deep soil layer, the ratio of soil microbial biomass carbon and nitrogen to total organic carbon and total nitrogen in rubber forest was 0.32%?0.88% and 0.83% ?0.98%,respectively; and the ratio of dissolved organic carbon and nitrogen to total organic carbon and total nitrogen was 0.18%?0.35%and 1.66%?2.95%. In the lm deep soil layer of Eucalyptus plantation, the ratio of soil microbial biomass carbon and nitrogen to total organic carbon and total nitrogen in the Eucalyptus plantation was 1.11%?0.24% and 0.21%?1.12%,respectively. The dissolved organic carbon and nitrogen accounted for total organic carbon and total nitrogen the proportions were 0.35%?0.48% and 0.69%?0.50%,respectively.2. The changes of soil enzyme activity in Rubber plantation was urease 0.04 ?0.41 mg · g-1,catalase 0.12 ?1.87 ml·g-1,polyphenol oxidase 1.74 ?9.10 ml·g-1. And the soil urease of 20 and 25 years old rubber forest had a higher activities than other ages, the same as DOC. The changes of soil enzyme activity in Eucalyptus plantation was urease 0.04 ?0.41 mg · g-1,catalase 0.12 ?1.87 ml · g-1,polyphenol oxidase 1.74 ?9.10 ml · g-1. And the changes of soil urease activity in Eucalyptus plantations of different age were consistent with the changes of soil DON. The results showed that soil urease activity was closely related to soil DON. In the vertical section of lm deep, the activities of soil urease and catalase in both of Rubber and Eucalyptus plantation showed that that upper soil layers were higher than deeper soil, while polyphenol oxidase showed that deeper soil layers were higher than upper soil layers. However, there was no significant difference in soil polyphenol oxidase activity between different soil layers.3. There are close relationships between the active organic carbon and nitrogen in the soil and other soil factors in Rubber plantation, and soil active organic carbon and nitrogen had a significant or no significant negative correlation with soil Polyphenol oxidase, C / N ratio, water content and soil bulk density, indicating that these four soil factors were negative related to the distribution of soil activity in Rubber plantation ecosystem. Other soil factors have a positive interaction with the content of activated organic carbon and nitrogen. The correlation between different soil factors is that the correlation between soil DOC content and DON (r=0.789), MBN (r=0.727) and TN (r=0.736) was higher than other factors, which indicated that the soil DOC content in rubber forest was closely related to different forms of nitrogen. In addition, the dependence of soil MBC, MBN, DOC and DON on soil TN (r = 0.588, 0.764, 0.736, 0.527) was higher than that of SOC (r = 0.479,0.534, 0.504, 0.501), and the correlation between soil urease and catalase activity and soil TN (r = 0.407, 0.784) was also higher than SOC (r = 0.328, 0.289). It is further suggested that soil nitrogen may be one of the important factors limiting soil sustainable productivity in Rubber plantation ecosystem.4. The soils factors of Eucalyptus plantation also interact with each other. Soil C/N ratio and water content had negative effects on soil active organic carbon and nitrogen, and the negative effect of water content was significant, and other factors (except soil bulk density) was significant positive correlations with and soil active organic carbon nitrogen.Soil microbial entropy was significant positive correlation with soil MBC, MBN and DOC(r = 0.938, 0.665, 0.517) in Eucalyptus plantation. In addition, the correlation between soil urease and polyphenol oxidase activity and soil nutrient factor was higher than that of polyphenol oxidase, and the correlation coefficients of urease activity with soil MBC,MBN, DOC and DON (r=0.723, 0.931, 0.749, 0.726) were higher than that of catalase(r=0.571,0.424,0.558,-0.293) .Besides,there was a significant positive correlation between soil urease activity and SOC (r = 0.888) and TN (r = 0.848),while the other two enzymes had no significant relationship with SOC and TN. The results showed that there was a significant positive correlation between soil urease activity and soil nutrient factors in Eucalyptus plantation ecosystem, which could be used as an index to evaluate the health status of soil ecosystem of Eucalyptus plantation.5. The results of stepwise linear regression analysis showed that the effect of soil activity organic carbon and nitrogen factors on the soil enzyme activity was higher than that of soil SOC and TN. It was further suggested that soil MBC, MBN, DOC, DON had a more sensitive indicator of soil enzyme activity than soil SOC and TN, and it was an effective index to monitor soil enzyme distribution and change. |
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